introgression into tuber-bearing Solanum species is virtually excluded
due to constraints of geographical isolation and other biological
barriers to natural hybridization (Ref. 49). These barriers include
incompatible (unequal) endosperm balance numbers that lead to endosperm
failure and embryo abortion, multiple ploidy levels, and
incompatibility mechanisms that do not express reciprocal genes to
allow fertilization to proceed. No natural hybrids have been observed
between these species and cultivated potatoes in the United States.
    The body of information EPA consulted on potato also indicates that
the crop is not currently weedy or invasive in the United States.
According to the OECD consensus document, ``[o]utside the field, potato
seedlings will have difficulty establishing themselves as they cannot
compete with other plants. Love et al., 1994 report that these
seedlings are limited to cultivated areas for reasons of competition
and adaptation. Potato tubers can be spread during transportation and
use, but generally these plants will not be established for a long time
due to unfavourable environmental conditions. In general, the potato is
not known as a coloniser of unmanaged ecosystems'' (Ref. 48). One
expert EPA consulted indicated potato ``is a rare weed in potato plots
but it never becomes feral in the United States'' (Ref. 42).
    Finally, there is no reason to believe that acquisition of virus
resistance would make potato weedy or invasive, as viruses are not
consistently associated with failure of potato to show any evidence of
being weedy or invasive. The experts that EPA consulted agree that it
is not very likely that potato would become feral or easily spread into
non-crop areas if it acquired transgenic virus resistance. For example,
one expert consulted indicated that ``[t]he basis of poor survival of
cultivars in natural habitats is not due to virus susceptibility''
(Ref. 42). EPA therefore believes that potato meets the conditions
recommended by the 2005 SAP for inclusion on the list and will present
low risk with respect to weediness.
    y. Soybean. EPA proposes that soybean (Glycine max) be included on
the list in Sec.  174.27(a)(1) based on literature that is available on
soybean biology, the OECD Consensus Document on the Biology of Glycine
max (L.) Merr. (Soybean) (Ref. 50), and EPA consultations with soybean
experts. This body of information indicates that soybean meets the
three conditions outlined above by the SAP: It does not have wild or
weedy relatives in the United States with which it can form viable
hybrids in nature, it is not currently weedy or invasive in the United
States, and there is no reason to believe that acquisition of virus
resistance would make soybean weedy or invasive, as viruses are not
consistently associated with failure of soybean to show any evidence of
being weedy or invasive. All four experts contacted by EPA indicated
agreement with these statements. For example, one expert stated,
``Acquiring transgenic virus resistance will not change the ability of
soybean to become feral since it will still be a domesticated species
and does not have the attributes to

survive without human intervention. Virus diseases in the U.S. do not
generally cause major yield loses [sic] and resistance to some viruses
is very common in soybean. Transgenic virus resistance will not
substantially change how the soybean interacts with most environments''
(Ref. 42). According to the OECD consensus document, ``[t]he soybean
plant is not weedy in character. In North America, Glycine max is not
found outside of cultivation. In managed ecosystems, soybean does not
effectively compete with other cultivated plants or primary
colonizers'' (Ref. 50). EPA therefore believes that soybean meets the
conditions recommended by the 2005 SAP for inclusion on the list and
will present low risk with respect to weediness.
    z. Starfruit. EPA proposes that starfruit (Averrhoa carambola) be
included on the list in Sec.  174.27(a)(1) based on EPA consultations
with starfruit experts. These consultations indicate that starfruit
meets the three conditions outlined above by the SAP. One, it does not
have wild or weedy relatives in the United States with which it can
form viable hybrids in nature. One expert mentioned that starfruit can
hybridize with wild Averrhoa carambola, but another expert indicated
that researchers have concluded wild starfruit trees can no longer be
found in the United States (Ref. 42). Second, these experts agreed that
starfruit is not currently weedy or invasive in the United States.
Third, these experts agreed that it is unlikely that acquisition of
virus resistance would make starfruit weedy or invasive. For example,
one expert stated, ``It is highly unlikely that starfruit with acquired
transgenic resistance would spread to non-crop areas because... seed
recalcitrance in starfruit... results in a loss of viability shortly
after harvest'' (Ref. 42). EPA therefore believes that starfruit meets
the conditions recommended by the 2005 SAP for inclusion on the list
and will present low risk with respect to weediness.
    aa. Sugarcane. EPA proposes that sugarcane (Saccharum officinarum)
be included on the list in Sec.  174.27(a)(1) based on EPA
consultations with sugarcane experts. These consultations indicate that
sugarcane meets the three conditions outlined above by the SAP. One, it
does not have wild or weedy relatives in the United States with which
it can form viable hybrids in nature. According to one expert,
``Although in theory it should happen in more tropical regions of the
world, hybrid seedlings among commercial or wild relatives are not
observed. Breeders routinely generate hybrids among commercial
sugarcane (derived from interspecific hybrids of Saccarhum [sic]
officinarum and S. sponteneum), and among commercial and wild relatives
(S. spontaneum mostly) under controlled conditions of heating and
photoperiod control. The resulting progeny are quite weak and must be
husbanded under greenhouse-type conditions prior to planting in the
field'' (Ref. 42). Second, these experts agreed that sugarcane is not
currently weedy or invasive in the United States. One expert stated,
``Commercial sugarcane is clonally propagated. Occasionally some of the
harvested cane may be lost from the trucks or wagons while in transport
from the field to the processing factory. If the cane has not been
burned prior to harvest, volunteer plants occasionally grow along the
transport route. This cane is not sexually reproducing, nor is it
invasive in nature. Simple roadside mowing or natural weather
conditions usually eliminate it'' (Ref. 42). Third, these experts
agreed that it is unlikely that acquisition of virus resistance would
make sugarcane weedy or invasive. For example, one expert stated,
``commercial sugar does not become a feral pest under regular
commercial production conditions. The majority of existing commercial
cultivars have been bred for genetic resistance to various disease-
causing sugarcane viruses. None of these cultivars have become feral or
a pest in anyway [sic]'' (Ref. 42). EPA therefore believes that
sugarcane meets the conditions recommended by the 2005 SAP for
inclusion on the list and will present low risk with respect to
weediness.
    bb. Tulips. EPA proposes that tulips (Tulipa spp.) be included on
the list in Sec.  174.27(a)(1) based on EPA consultations with tulip
experts. These consultations indicate that tulips meet the three
conditions outlined above by the SAP. One, they do not have wild or
weedy relatives in the United States with which they can form viable
hybrids in nature. Two, they are not currently weedy or invasive in the
United States, although two experts indicated that Tulipa sylvestris
naturalizes in certain areas without being viewed as a significant
problem because it reproduces only vegetatively. Three, there is no
reason to believe that acquisition of virus resistance would make
tulips weedy or invasive. One expert noted that this was ``possible,
but unlikely. Virus resistance could conceivably increase the vigor of
the vegetative spread of T. sylvestris'' (Ref. 42). However, three
other experts believed that this was highly unlikely to occur. One
said, ``The need for chilling in this genus means that it is restricted
to temperate areas with summer-cool climates. Areas where it can
persist are very limited and there is a high degree of browsing of this
genus by vertebrates such as deer that make seed production in the wild
a very rare occurrence in nature in the U.S.'' (Ref. 42). EPA therefore
believes that tulips meet the conditions recommended by the 2005 SAP
for inclusion on the list and will present low risk with respect to
weediness.
    ii. Adding plants to the categorical exemption criterion in Sec.
174.27(a)(1). As the Agency gains additional experience, it may propose
to add crops to the list. In addition, any person may petition the
Agency to add particular crops to the list. EPA would evaluate any
potential candidates against the same considerations used in this
rulemaking to develop the list in Sec.  174.27(a)(1) discussed above.
Consequently, for a petition to be successful, it should contain
sufficient data or other information to allow EPA to perform such an
analysis, e.g., published information or a consensus opinion among
experts in the particular crop that addresses the questions EPA posed
in its expert consultations (discussed in Unit III.C.2.i.). Petitioners
are welcome to consult with EPA prior to preparing a submission to
discuss the information that would be required. EPA would consult with
USDA in evaluating petitions for adding plants to Sec.  174.27(a)(1).
    Any subsequent addition of crops to the list in Sec.  174.27(a)(1),
either through the Agency's own initiative or in response to a petition
from the public, may only occur through rulemaking. Under FIFRA section
25, rulemaking involves several steps, including reviews by the SAP and
USDA. In general, EPA would seek to expedite the process and proceed
through direct final rulemaking where feasible. Under such a process,
in cases where EPA believes that the proposal will not raise
scientifically complicated issues, EPA would simultaneously issue a
final rule and a proposal. If no adverse comments were received, the
final rule would go into effect and EPA would withdraw the proposed
rule. In the event of adverse comment, EPA would withdraw the final
rule and would proceed to issue a final rule that addressed the public
comments received on the proposal. In addition, as part of this current
rulemaking, because EPA's analysis to determine whether to add a crop
to the list would be consistent with the criteria provided by the SAP,
the Agency would request that the SAP generally waive its

review of subsequent rules seeking to add further crops to the list in
Sec.  174.27(a)(1) unless EPA subsequently determines that a particular
rule raised novel or particularly complex scientific issues.
    iii. Proposed exemption criterion conditional on Agency
determination in Sec.  174.27(a)(2). EPA recognizes that many PVCP-PIP/
plant combinations would reasonably be expected to pose low risk with
respect to weediness even though the crop plant containing the PVCP-PIP
is not on the Agency's proposed list in Sec.  174.27(a)(1). EPA has not
conducted an exhaustive survey of all crop plants to evaluate them for
inclusion on this list and therefore recognizes that additional plants
may meet the conditions that were used to compile this list of plants.
Therefore, in addition to the categorical exemption criterion, EPA also
believes that a criterion conditional on Agency determination could be
developed that would identify plants that are low risk with respect to
weediness.
    EPA is considering four options for such a conditional exemption
criterion under which PVCP-PIP/plant combinations that fail to meet
Sec.  174.27(a)(1) could still meet Sec.  174.27(a) under Sec.
174.27(a)(2), subject to an Agency review. Each of the options reflects
a somewhat different approach to implementing the recommendations of
the 2005 SAP (Ref. 11). EPA does not currently have a preferred
approach and presents several options to promote full consideration of
the issues, although option 1 is presented in the regulatory text so
the public could see how Sec.  174.27(a)(2) might fit into the overall
framework of the exemption.
    a. Option 1. The first option for Sec.  174.27(a)(2) provides the
strictest interpretation of the 2005 SAP advice. Under this option, a
PVCP-PIP would meet Sec.  174.27(a) under Sec.  174.27(a)(2) if the
Agency determines after review that the plant containing the PIP meets
all of the following:
    (i) Has no wild or weedy relatives in the United States with
which it can form viable hybrids in nature.
    (ii) Is not a weedy or invasive species outside of agricultural
fields in the United States.
    (iii) Is unlikely to establish weedy or invasive populations
outside of agricultural fields in the United States even if the
plant contains a PVCP-PIP.

    EPA would expect exemption submissions to document that the plant
meets these conditions in the opinion of agronomists, breeders,
ecologists, and other experts working with the specific taxa in
question or based on data. When these conditions are met, the
likelihood that a PVCP-PIP could cause increased weediness of any plant
would be very small, as discussed in the following paragraphs.
    If the plant containing the PVCP-PIP has no wild or weedy relatives
in the United States with which it can form viable hybrids in nature
and thus would meet the criterion in Sec.  174.27(a)(2)(i) under option
1, it would not be possible for the PVCP-PIP to inadvertently be
transferred to any wild or weedy relatives, e.g., through pollen flow.
Whether the recipient plant ``can produce viable hybrids in nature'' is
a critical attribute that would definitively determine the potential
for introgression of the PVCP-PIP into a native or naturalized plant
population. Although hybrids must be able to reproduce themselves in
order for introgression to occur, the production of ``viable'' hybrids
(i.e., those that are able to grow) may be described more clearly in a
regulatory standard than examining the reproductive potential of any
hybrids. In many cases, reproductive potential of hybrids has not been
fully investigated. Given that reduced fertility in F1 crop-wild
hybrids is frequently restored to normal in subsequent generations
(Ref. 37), measurement of hybrid fertility involves consideration of
several generations. In addition, viability is a more reliable standard
because even very low rates of gene transfer could lead to
introgression (Ref. 51), suggesting that any degree of hybrid fertility
could indicate the potential for introgression to occur. As noted by
the 2005 SAP, ``it is known that favorable alleles (including, perhaps,
a PVCP-PIP) can pass easily from one species to another through hybrid
zones, even when the hybrids have very low fitness (Barton 1986)''
(Refs. 11 and 52). The Agency recognizes that introgression of a trait
such as virus resistance into natural plant populations does not
automatically confer a competitive advantage to the recipient
population. However, at this time, there is little information
available to predict categorically whether acquisition of such a trait
might affect the competitiveness of a specific plant population, and
the available information does not allow the Agency to make this
determination a priori. The ability to produce viable hybrids is
relatively easy to evaluate, resulting in a clear criterion that
ensures an effective limitation on the potential for introgression.
Such language also clarifies that the relevant question is whether the
hybrid can be produced ``in nature.'' The fact that plants could be
crossed in the laboratory or greenhouse is not necessarily indicative
of a plant's true reproductive potential. The Agency's focus is whether
a viable hybrid could be produced under normal growing conditions in
the field or in nature, rather than under controlled experimental
conditions that might have little relevance to behavior in the
environment.
    If the plant containing the PVCP-PIP is not a weedy or invasive
species outside of agricultural fields in the United States and thus
would meet the criterion in Sec.  174.27(a)(2)(ii) under option 1,
established and persistent feral populations of the crop presenting
difficult management issues in natural or semi-managed ecosystems would
be unlikely. Thus, transfer of the PVCP-PIP from the crop to a feral
population would be unlikely to exacerbate what could already be a
difficult problem by inadvertently increasing the population's
weediness potential. EPA proposes inclusion of the term ``outside of
agricultural fields'' to emphasize that the key consideration is the
plant's behavior in natural settings, including semi-managed habitat
surrounding agricultural fields as opposed to its behavior within the
fields themselves. EPA recognizes that most crops within agricultural
fields form volunteer populations, where propagules of the crop from
the previous rotation grow in the subsequent crop rotation. The Agency
believes the language ``outside of agricultural fields'' appropriately
excludes this situation from consideration.
    If the plant containing the PVCP-PIP is unlikely to establish weedy
or invasive populations outside of agricultural fields in the United
States even if the plant contains a PVCP-PIP and thus would meet the
criterion in Sec.  174.27(a)(2)(iii) under option 1, an additional
level of assurance would be provided that the crop plant would not
present weediness concerns through acquisition of a PVCP-PIP. EPA
believes that this condition could in general be met based on the
opinion of experts on the particular crop. Experts may judge, for
example, that acquisition of virus resistance is unlikely to change the
weedy or invasive characteristics of the plant if the crop does not
appear to be weedy or invasive when virus infection is known to be
absent from a particular area or over a particular period of time.
Available empirical data could be used in the determination or may be
gathered if expert opinion cannot resolve the question.
    EPA proposes to define the term ``weedy species'' used in Sec.
174.27(a)(2)(ii) to mean ``a species that

is an aggressive competitor in natural ecosystems.'' EPA intends to use
the term ``invasive species'' consistent with the definition in
Executive Order 13112, meaning an alien species whose introduction
causes or is likely to cause economic or environmental harm or harm to
human health. An alien species means, with respect to a particular
ecosystem, any species, including its seeds, eggs, spores, or other
biological material capable of propagating that species, that is not
native to that ecosystem. EPA uses the phrase ``weedy or invasive
populations'' in Sec.  174.27(a)(2)(iii) consistent with these
definitions.
    EPA notes that the criterion in Sec.  174.27(a)(2)(i) under option
1 does not necessarily strictly hold for every crop that appears on the
list in proposed Sec.  174.27(a)(1). In some cases, EPA was able to
make a low risk determination for a particular crop, e.g., corn, in
spite of the possible presence of wild or weedy relatives in the United
States with which the plant may in rare cases form viable hybrids in
nature. EPA has presented the basis for such conclusions in this
proposed rule, and the public can clearly understand why the crops in
Sec.  174.27(a)(1) meet the Agency's low risk standard with respect to
weediness concerns. Given that several crops for which EPA has made a
low risk determination and proposes to include in Sec.  174.27(a)(1)
would not meet Sec.  174.27(a)(2) as proposed under option 1, EPA
believes that option 1 may be too narrow. Accordingly, EPA is
considering other options for Sec.  174.27(a)(2) that are based on a
less literal interpretation of the SAP's recommendations but which the
Agency believes are nevertheless consistent with the SAP's intent.
    b. Option 2. The second option EPA is considering is that a PVCP-
PIP would meet the criterion in Sec.  174.27(a)(2)(i) if ``the plant
containing the PIP has no wild or weedy relatives in the United States
with which it can form viable, fertile hybrids in nature, or if
fertile, the resulting hybrid cannot establish populations in the
environment.'' EPA is considering this option because most crops are
able to form viable hybrids with a wild or weedy relative in some part
of the United States. However, some viable, fertile hybrids may
nevertheless present low risk with respect to concerns associated with
weediness, e.g., if the hybrids are weak and lack the ability to
establish. On the other hand, fertility and the potential to establish
are more difficult characteristics to evaluate than viability because
many more variables affect the determination, suggesting that it might
be more appropriate in these cases for the Agency to require that data
be collected for a period of time after commercial deployment that
could confirm the Agency's original analysis. However, while such
conditions may be readily placed on a PVCP-PIP registration, they could
not be placed on an exempt PVCP-PIP. In addition, determinations under
option 2 would be more difficult for the public to predict than
determinations under option 1, as discussed in Unit III.A.2.
    c. Option 3. Under the third option being considered, EPA would
adopt only the criteria in Sec.  174.27(a)(2)(i) and (a)(2)(ii) as
discussed above under option 1. The rationale for such an approach is
that it may not be necessary to evaluate the criterion in Sec.
174.27(a)(2)(iii) in order to make a low risk determination because the
issues are adequately addressed by the other two criteria. Viruses
generally do not uniformly affect crops every season in every place
they are planted - even those crops that viruses significantly impact
such that development of a PVCP-PIP to combat the disease might be
undertaken. Crops will thus have repeated opportunity to escape
cultivation in seasons and in areas where there is no virus
infestation. If weedy tendencies are rarely or never observed in any
part of the crop's range, it is unlikely that virus resistance affects
the crop's ability to escape cultivation and establish weedy
populations. Unlike wild or weedy plant relatives that may at times be
infected by viruses and may be negatively impacted by viruses in ways
that are not obvious to untrained observers, breeders and farmers are
intimately aware of the type of damage done by virus infection to crops
and are therefore well aware when their fields are or are not infected.
Crop plants have been observed under a diverse range of environmental
conditions over many years. If a PVCP-PIP were likely to make a crop
weedy or invasive, such tendencies would likely have been observed even
without virus resistance at some point in time given the level of
observation crops generally receive due to the necessity to actively
manage their cultivation. Such crops showing weedy or invasive
tendencies would not meet the criterion in Sec.  174.27(a)(2)(ii),
suggesting that the criterion in Sec.  174.27(a)(2)(iii) is largely
redundant with this condition.
    EPA notes that option 3 is likely to be equally as narrow as
options 1 and 2. The advantage of the option would be a simplification
of the issues that a PVCP-PIP developer would need to address as part
of a submission for an exemption determination.
    EPA could consider factors that are not considered under options 1-
3 but that would affect the potential impact of PVCP-PIP acquisition as
part of evaluating a PVCP-PIP for FIFRA registration. For example, EPA
could take into account the effect of virus infection on such species,
the existence and impact of any natural virus resistance in the
population, the overlap of the plant's distribution with crop
cultivation areas, and other relevant considerations.
    d. Option 4. The fourth option EPA is considering is that a PVCP-
PIP would meet Sec.  174.27(a)(2) if the Agency determines that ``the
PVCP-PIP is unlikely to significantly change the population size or
distribution of the species containing the PVCP-PIP outside of
agricultural fields or the population size or distribution of any wild
or weedy species in the United States that could acquire the PVCP-PIP
through gene transfer.'' EPA is considering this fourth option because
the Agency recognizes that many PVCP-PIPs excluded from exemption under
the criterion in Sec.  174.27(a)(2)(i) of options 1-3 because of wild
or weedy relatives in the United States may nevertheless present low
risk. The presence of wild or weedy relatives relates only to potential
exposure of the PVCP-PIP and does not indicate whether the PVCP-PIP is
likely to cause any adverse effects even if it were to transfer to
these relatives. EPA believes that such an evaluation would be
consistent with the advice of the 2005 SAP, which noted that ``[t]he
probability that a particular transgene will lead to increased
weediness depends on the phenotype conferred by the transgene and on
the ecological factor(s) currently limiting the size or distribution of
the wild species. In particular, if the transgene alters plant response
to an ecological factor limiting population size, then population
dynamics may be affected. For PVCP-PIPs, the relevant consideration is
whether virus resistance (conferred by the PVCP-PIP) leads to changes
in the size or distribution of wild plant species with the PVCP-PIP''
(Ref. 11).
    With option 4, EPA would conduct a risk assessment to evaluate a
clear end point - whether there is likely to be a significant change in
the population size or distribution of the species containing the PVCP-
PIP outside of agricultural fields or the population size or
distribution of any wild or weedy species in the United States that
could acquire the PVCP-PIP through gene transfer. However, for the vast
majority of species, many characteristics that would influence this
determination are

currently poorly understood, e.g., the impact of virus infection on
wild plant populations and the likely selective advantage afforded by
acquisition of virus resistance. As a result, both the nature of EPA's
evaluation and the type and extent of data that might need to be
provided to the Agency resemble much more closely what would be
required to evaluate weediness issues during a FIFRA registration
review. In addition, the more the exemption determination process
resembles a full risk assessment, the longer the time required for EPA
to complete such a review.
    Although EPA would seek public comment on determinations that a
PVCP-PIP met Sec.  174.27(a)(2) according to the procedure for
exemptions utilizing any Agency-determined criteria, Agency
determinations may be more controversial with this option than with
other options that have more clearly defined criteria. EPA believes
that case-by-case determinations could be made appropriately and that
the data requirements needed to evaluate the criterion under option 4
would not necessarily be overly burdensome. EPA notes that in many
cases much of the data, if not all, needed for EPA to evaluate a
criterion such as this fourth option would also be needed for a
petition for determination of nonregulated status submitted to USDA.
EPA believes that the flexibility of this option will make it more
likely that the Agency would identify the largest number of low risk
products that could qualify for exemption.
    For all options for proposed Sec.  174.27(a)(2), the Agency
believes the entire United States is the relevant scope of inquiry
because the proposed exemption would carry no limitations on where the
exempted PVCP-PIP/plant combination could be planted and thus could be
planted in all areas subject to U.S. law. FIFRA section 2(aa) defines
``State'' as ``a State, the District of Columbia, the Commonwealth of
Puerto Rico, the Virgin Islands, Guam, the Trust Territory of the
Pacific Islands, and American Samoa. Accordingly, the term ``United
States'' used in this proposal includes all these areas, and EPA
proposes to incorporate a definition of ``United States'' paralleling
the FIFRA definition of ``State'' into the definitions in 40 CFR 174.3.
    As an alternative to Agency review pursuant to Sec.  174.27(a)(2),
a developer could petition EPA to add a crop to the list in Sec.
174.27(a)(1). In some cases, EPA expects that the same data/information
that would support a determination that a crop meets Sec.  174.27(a)(2)
would support listing the crop in Sec.  174.27(a)(1). However, because
a plant can only be added to the list in Sec.  174.27(a)(1) through
rulemaking, EPA expects that many developers will instead prefer to
obtain an Agency determination under Sec.  174.27(a)(2). However, once
a plant is added to the list in Sec.  174.27(a)(1), future PVCP-PIPs
used in that plant would meet Sec.  174.27(a) without any Agency
review.
    3. Historical approaches. In 1994 EPA proposed two different
alternatives for exempting PVCP-PIPs from FIFRA requirements. The
Agency prefers the approaches discussed in the preceding Subunit
because they have been developed based on recent interactions with the
SAP and thus represent the most current science. One 1994 alternative
contained exemption criteria directed towards addressing concerns
associated with gene transfer to identify those PVCP-PIP/plant
combinations with the lowest potential to confer selective advantage on
wild or weedy plant relatives. EPA described this alternative exemption
as follows:
    Coat proteins from plant viruses [would be exempt] if the
genetic material necessary to produce a coat protein is introduced
into a plant's genome and the plant has at least one of the
following characteristics:
    (1) The plant has no wild relatives in the United States with
which it can successfully exchange genetic material, i.e., corn,
tomato, potato, soybean, or any other plant species that EPA has
determined has no sexually compatible wild relatives in the United
States.
    (2) It has been demonstrated to EPA that the plant is incapable
of successful genetic exchange with any existing wild relatives
(e.g., through male sterility, self-pollination).
    (3) If the plant can successfully exchange genetic material with
wild relatives, it has been empirically demonstrated to EPA that
existing wild relatives are resistant or tolerant to the virus from
which the coat protein is derived or that no selective pressure is
exerted by the virus in natural populations (59 FR 60504, November
23, 1994).

    EPA carefully reconsidered this 1994 proposal in its deliberations
for today's proposed exemption and presented these criteria in modified
form to the FIFRA SAP at the October 2004 and December 2005 meetings
for consideration. In light of comments received from the FIFRA SAP and
additional scientific information available since 1994, EPA no longer
believes this alternative would adequately address questions associated
with weediness in a manner that could be reasonably implemented.
However, EPA still considers that it would be appropriate to limit the
exemption based on the concerns outlined in the earlier proposal
associated with acquisition of virus resistance through hybridization
with a transgenic plant containing a PVCP-PIP.
    Although similar in intent to characteristic (1) of this option
proposed in 1994, today's proposed criterion in Sec.  174.27(a)(2)(i)
under option 1 focuses in part on the potential to ``form viable
hybrids in nature'' rather than simply ``exchange genetic material''
because the former is a clearer standard for determining whether a
PVCP-PIP could have the potential to affect a recipient plant
population negatively. The ability to exchange genetic material, which
is often demonstrated by performing hand crosses in the laboratory or
greenhouse, may not indicate any relevant information about how the
plants would behave in nature. Today's proposed criterion in Sec.
174.27(a)(1) also uses a somewhat different list of plants than the
four in the 1994 proposal. Several species have been added (see Unit
III.C.2.i.) and tomato has been removed from the list because of
information acquired through expert consultation. (See Unit VII for a
discussion of this information and to read EPA's request for comment).
When EPA presented a criterion similar to the first characteristic in
the 1994 proposal to the 2004 SAP, they responded that ``the Panel was
of the opinion that the absence of a competent wild/weedy relative
positioned in relation to the plant containing the PVCP-PIP was an
appropriate condition.'' The 2005 SAP also ``was supportive of the
Agency's intent to exempt from regulation any PVCP-PIP crops that (1)
do not have sexually compatible wild relatives in the location of
intended cultivation (US & Territories) and (2) are not likely to
become weedy themselves'' (Ref. 11).
    EPA now also believes that characteristic (2) of the option
proposed in 1994 may be insufficient based on the conclusions of the
2004 SAP and the National Research Council that current methods of
bioconfinement are imperfect and are unlikely to adequately restrict
gene flow (Refs. 25 and 53). The Agency asked the 2004 SAP whether the
condition that ``genetic exchange between the plant into which the
PVCP-PIP has been inserted and any existing wild or weedy relatives is
substantially reduced by modifying the plant with a scientifically
documented method, (e.g., through male sterility)'' would be necessary
and/or sufficient to minimize the potential for a PVCP-PIP to harm the
environment through gene transfer from the crop plant containing the
PVCP-PIP to wild or weedy relatives. The Panel ``accepted that tactics
aiming at diminished gene exchange are highly desirable and even
necessary but are not sufficient'' (Ref. 25).

    In spite of such concerns, EPA is still considering whether a
criterion involving biocontainment could be sufficient to enable the
Agency to determine with review that a product presents low risk with
respect to concerns associated with weediness. The 2005 SAP concluded
``that if highly effective biological containment and biological
mitigation methods could be deployed concurrently with the PVCP-PIP,
then it would be possible to exempt crops with sexually compatible wild
relatives. This opinion is different from the opinion of the October
2004 FIFRA SAP. The [2005] Panel concluded that this difference is
probably due to advances in containment and mitigation strategies. For
this reason, exemptions might be granted to any crop that hybridizes
with a wild relative in the US, its possessions or territories, if the
F1 and BC (backcross) hybrids have very low fitness such
that it is effectively lethal. Additionally, an exemption might be
possible if specific genes for lowering fitness are in tandem
constructs with the PVCP-PIP gene in such a way that they cannot
readily segregate from each other. The Panel did not determine what
level of effectiveness would be required but, it was agreed that
stacked strategies would reduce the cumulative risk, and should be
strongly considered'' (Ref. 11).
    Bioconfinement strategies are known to have a wide range of
efficacy, and no standard level of efficacy to ensure environmental
safety has been determined (Ref. 53). Additionally, some techniques may
introduce risk concerns that must be evaluated, e.g., unintended
impacts on wildlife that eat seeds or pollen (Ref. 25). However,
scientific advancements may make bioconfinement techniques sufficiently
reliable and safe in the future such that deployment with a PVCP-PIP
would be sufficient to reach a low risk finding with respect to
concerns associated with weediness (Refs. 54 and 55). Therefore, EPA is
still considering a condition such as characteristic (2) proposed in
1994 that would constitute an alternative way to meet Sec.
174.27(a)(2) under any of the options discussed in this Preamble. For
example, Sec.  174.27(a)(2) might read:
    The Agency determines after review that the plant containing the
PIP:
    (i) Has no wild or weedy relatives in the United States with
which it can form viable hybrids in nature or employs a highly
effective biological containment technique.
    (ii) Is not a weedy or invasive species outside of agricultural
fields in the United States or employs a highly effect biomitigation
construct that ensures escapes from cultivation are too unfit to
compete with wild-types.

    EPA believes that characteristic (3) of the option proposed in 1994
is sound conceptually. However, the Agency's intent in developing this
exemption has historically been to have criteria that identify low risk
PVCP-PIPs such that the criteria could be evaluated with information
that a developer is likely to have acquired in the course of developing
the product and not require significant data generation. The Agency
presented a similar criterion to the 2004 SAP for their consideration:
``all existing wild or weedy relatives in the United States with which
the plant can produce a viable hybrid are tolerant or resistant to the
virus from which the coat protein is derived.'' The Panel members
suggested that such a criterion would be difficult to implement in a
clear and transparent exemption review process given that ``[t]he Panel
had particular difficulty when attempting to add precision to
approaches that should be followed when sampling wild and weedy
relatives for the occurrence of specific virus tolerance or resistance
as specified by the Agency.''
    As an alternative to a criterion like that described by
characteristic (3) in the 1994 proposal whose evaluation would
necessitate collection of potentially significant amounts of data, EPA
presented another option to the 2005 SAP: ``(i) the plant containing
the PVCP-PIP is itself not a weedy or invasive species outside of
agricultural fields in the United States, its possessions, or
territories, and (ii) the plant containing the PVCP-PIP does not have
relatives outside of agricultural fields in the United States, its
possessions, or territories that are weedy or invasive species or
endangered/threatened species with which it can produce viable hybrids
in nature'' (Ref. 11). However, the Panel concluded that ``the
probability that a particular transgene alters the dynamics of a wild
relative cannot be predicted by the current status of the wild species
as weedy, invasive, or threatened/endangered. The Panel agreed that the
criteria proposed by the Agency would not correctly identify PVCP-PIPs
which pose unacceptable environmental risks'' (Ref. 11). EPA has
therefore concluded that the Agency is unable at this time to
articulate a clear criterion for exemption that would expand the
eligible plants beyond those roughly described by the ideas in the 1994
characteristic (1) unless the Agency were to adopt a criterion whose
evaluation involved conducting a risk assessment of the PVCP-PIP/plant
combination such as it put forth in this preamble as the fourth option
for proposed Sec.  174.27(a)(2), i.e., that the PVCP-PIP is unlikely to
significantly change the population size or distribution of the species
containing the PVCP-PIP outside of agricultural fields or the
population size or distribution of any wild or weedy species in the
United States that could acquire the PVCP-PIP through gene transfer
(discussed in Unit III.C.2.iii.d.).
    The other alternative proposed in 1994 did not contain a criterion
addressing concerns associated with gene flow. This option proposed a
full categorical exemption for all PVCP-PIPs (59 FR 60503). This option
is no longer the Agency's preferred approach for a number of reasons.
Specifically, EPA has received scientific advice since issuance of the
1994 proposal calling into question the Agency's 1994 rationale that
all PVCP-PIPs meet the FIFRA 25(b)(2) exemption standard, including
gene flow considerations. Although EPA believes that many PVCP-PIPs
present low risk and thus meet the FIFRA 25(b)(2) exemption standard,
in order to categorically exempt all PVCP-PIPs, the Agency must be able
to draw this conclusion for all PVCP-PIPs. Advances in scientific
understanding since 1994 suggest it may not be possible to support this
rationale for all PVCP-PIPs and that certain PVCP-PIPs may pose a
greater level of risk than is characteristic of the group as a whole.
For example, virus resistance is common in natural plant populations as
evidenced by conventionally bred virus resistant plants that are only
possible due to naturally existing resistance in crop and wild relative
populations (Ref. 20). This fact suggests that acquisition of virus
resistance is often unlikely to introduce a novel trait into many plant
populations. However, some notable exceptions to the ubiquity of virus
resistance in natural plant populations exist including the lack of
successful conventionally bred resistance to barley yellow dwarf virus
in major crops and the lack of natural resistance in some wild
relatives of these crops (Ref. 36). Such information suggests that
acquisition of a PVCP-PIP by such wild relatives of these plants has
the potential to free these wild relatives from what may be an
important ecological constraint. The conclusions of the 2004 FIFRA SAP
are consistent with the idea that it may not be possible to apply a
general exemption rationale to all PVCP-PIPs. The report concluded that
``...PVCP-PIPs [have] no inherent capacity to harm the environment.''
However, ``[i]t was recognized that knowledge of hybridization
potential was sparse and of very unequal quality but the likelihood of
serious economic

harm was such that some plants engineered to contain stress tolerant
traits should not be released'' (Ref. 25). The 2005 SAP's conclusions
discussed above also clearly suggest that crops containing a PVCP-PIP
that have wild relatives must be carefully considered on a case-by-case
basis (Ref. 11). Similarly, the 2000 National Research Council (NRC)
report recommended that because of concerns associated with
hybridization with weedy relatives, ``EPA should not categorically
exempt viral coat proteins from regulation under FIFRA. Rather, EPA
should adopt an approach, such as the agency's alternative proposal...,
that allows the agency to consider the gene transfer risks associated
with the introduction of viral coat proteins to plants'' (Ref. 10).

D. Viral Interactions

    1. Scientific issues. In addition to weediness, a key issue
associated with PVCP-PIPs is the question of whether they could affect
the epidemiology and pathogenicity of plant viruses. Given the
potential impact of virus infection, such changes might affect
competitiveness of plant populations thereby altering ecosystem
dynamics, e.g., through significant changes in species composition of
populations, resource utilization, or herbivory.
    The genetic material of plant viruses may be composed of either RNA
or DNA, although most have RNA genomes (Ref. 56). Although there are
significant differences between RNA and DNA viruses, both are obligate
parasites that usually move from plant to plant via vector-mediated
transmission. Such transmission, in connection with other types of
virus transmission, commonly leads to mixed viral infections in crops
and other plants (Ref. 57). In natural, mixed infections, viral genomes
from different strains and/or different species simultaneously infect
the same plant and thus have opportunities to interact (e.g., through
recombination, heterologous encapsidation, or synergy). In spite of
many opportunities for interaction in nature, such events rarely lead
to any detectable adverse outcome (Ref. 58). However, such in planta
interactions have the potential to result in a virus that causes
increased agricultural or other environmental damage.
    In transgenic plants containing PVCP-PIPs, every virus infection
can be considered in one sense to be a mixed infection with respect to
the coat protein gene (Ref. 59). The key questions facing EPA are
whether interactions between such introduced plant virus sequences and
infecting viruses in transgenic plants may increase in frequency or be
unlike those expected to occur in nature (Ref. 60). The Agency has
written a literature review addressing these questions (Ref. 60) and
will briefly describe the issues associated with recombination,
heterologous encapsidation, and synergy below. EPA provides a general
overview of each of the processes separately, followed by a brief
review of relevant field studies that investigated these processes.
    i. Recombination. Recombination is a natural process that can occur
during replication of DNA or RNA whereby new combinations of genes are
produced. Plant virus recombination can occur between members of the
same virus pathotype in natural infections, contributing to the number
of variants that exist within that pathotype. Recombination can also
occur when different viruses coinfect the same plant and interact
during replication to generate virus progeny that have genetic material
from each of the different parental genomes. Although recombination
likely occurs regularly in mixed viral infections, recombination only
rarely leads to viable viruses and even more rarely to viruses with
truly novel behavior and/or characteristics or any detectable adverse
outcome. In order to persist in nature, a recombinant virus must be
competitive with variants of the parental viruses that have already
demonstrated success in all stages of the infective cycle, e.g.,
transmission, gene expression, replication, and assembly of new virions
(Ref. 58). An analysis of cucumber mosaic virus (CMV) isolates in
natural populations showed that viable recombinants were very rarely
recovered in mixed infections (Ref. 61).
    Although selection in the field appears to act against persistence
of new, recombinant viruses, recombination is thought to play a
significant role in virus evolution, presumably because recombinant
viruses are on very rare occasions able to outcompete existing viruses.
How a virus with increased pathogenicity or altered epidemiology might
conceivably be created through recombination was suggested by a
laboratory experiment in which a pseudorecombinant strain was created
by experimentally combining regions of the CMV and tomato aspermy virus
(TAV) genomes. This artificially manipulated virus was found to cause
more severe symptoms than either of the parental genomes, although the
recombinant was not a fully-functional virus as it was not able to move
beyond the initially infected cells (Ref. 62) and would therefore not
be expected to persist in nature. Another laboratory experiment has
shown interspecific recombination between CMV and TAV under conditions
in which recombinants would not be expected to have any particular
fitness advantage (Ref. 63). In another example, alteration of the host
range of tobacco mosaic virus (TMV) occurred when a chimeric virus
expressed the coat protein from alfalfa mosaic virus (AMV) instead of
its own (Ref. 64).
    Evidence of past recombination having led to the creation of new
RNA viruses has been documented in a number of different groups
including bromoviruses (Ref. 65), luteoviruses (Ref. 66), nepoviruses
(Ref. 67), and cucumoviruses (Ref. 68). Sequence analysis of viruses
from the family Luteoviridae indicated that this family has evolved via
both intra- and interfamilial recombination (Ref. 69). Interspecific
recombination between two related potyviruses, soybean mosaic virus
(SMV) and bean common mosaic virus (BCMV) apparently led to the
creation of watermelon mosaic virus (WMV) with a broader host range
than either SMV or BCMV (Ref. 70). Whereas these latter two viruses are
generally restricted to Leguminosae, WMV has one of the broadest host
ranges among the potyviruses being able to infect both monocots and
dicots. For RNA viruses, evidence of recombinant viruses arising in
recent history has not been reported, suggesting that recombination as
a factor in RNA virus evolution may generally only be significant over
a longer timescale.
    Recombination has also played a role in the evolution of new DNA
viruses including caulimoviruses (Ref. 71) and geminiviruses (Refs. 72
and 73). For DNA viruses, geminiviruses in particular, several
instances can also be cited in which relatively recent recombination
events appear to have resulted in the creation of new viruses. For
example, a recent epidemic of severe cassava mosaic disease in Uganda
is thought to be due to the combination and/or sequential occurrence of
several phenomena including recombination, pseudorecombination, and/or
synergy among cassava geminiviruses (Ref. 72). It also appears that
tomato-infecting begomoviruses that have emerged in the last 20 years
around the Nile and Mediterranean Basins probably resulted from
numerous recombination events (Ref. 74). In addition, a natural
recombinant between tomato yellow leaf curl Sardinia virus and tomato
yellow leaf curl virus was detected in southern Spain with a novel
pathogenic phenotype that might provide it with selective advantage
over the parental genotypes (Ref. 75). Finally, analysis of

a newly described Curtovirus species associated with disease of spinach
in southwest Texas suggests that it may be the result of recombination
among previously described Curtovirus species (Ref. 76).
    In addition to virus-virus recombination, recombination has also
been found to occur between virus and plant host RNA. Sequence analysis
of the 5' terminal sequence of potato leafroll virus (PLRV) suggests
that it arose via recombination with host mRNA (Ref. 77). Evidence
suggests that such recombination events can affect virus virulence (for
review see Ref. 78). Like a plant host genome, transcripts of viral
transgenes would be available for recombination with infecting viruses,
and portions of the transgene could thus be incorporated into the
replicating virus. Several laboratory experiments have investigated the
potential for recombination between viral transgenes and infecting
viruses of the same species. These experiments show that recombination
can occur between viral transgenes and both RNA viruses (Refs. 79, 80,
81, 82, and 83) and DNA viruses (Refs. 84, 85, 86, and 87). However,
the relevance to PVCP-PIPs of the latter experiments with DNA viruses
is unclear because the transgenic plants used in the experiments
actually show no viral resistance; attempts to develop transgenic DNA
virus-resistant plants in general have had little success (Ref. 57). In
addition, to facilitate the detection of recombinants, most of these
experiments were conducted under conditions of high selective pressure
favoring the recombinant, i.e., only recombinant viruses were viable.
The selective pressure under normal field conditions would likely favor
the parental viruses rather than a recombinant as parental viruses will
be competent in all of the functions needed for propagation and will
outnumber the new recombinant.
    ii. Heterologous encapsidation. Heterologous encapsidation occurs
when the coat protein subunits of one virus surround and encapsidate
the viral genome of a different virus. The coat protein, possibly in
conjunction with other viral factors, is often essential for
transmission and responsible for conferring the high degree of vector
specificity. Therefore, a heterologously encapsidated viral genome may
be transmitted by the vectors of the virus contributing the coat
protein rather than the vectors of the virus contributing the viral
genome. For many viruses, transmission from plant to plant occurs by
insect vectors, and each virus tends to be transmitted by only one type
of insect (Ref. 1). To the extent that vectors visit different groups
of plants, vectors carrying a heterologously encapsidated viral genome
may carry it to a plant the virus does not normally encounter (Ref.
59).
    Most evidence of heterologous encapsidation is derived from
laboratory or greenhouse studies. Even though there is a high frequency
of mixed infections in nature, most mixed infections do not lead to
heterologous encapsidation, and those virus interactions that do occur
tend to be very specific rather than random interactions between
unrelated viruses (Ref. 88). Only among some types of plant viruses is
heterologous encapsidation regularly observed. Its frequency depends on
the relationship between the viruses involved, being more likely to
occur among closely related viruses (Ref. 89). An expansion of aphid
vector specificity due to heterologous encapsidation was first observed
in plants infected with two different isolates of barley yellow dwarf
virus (BYDV; Ref. 90) and was later shown to be a general phenomenon
among these viruses in natural populations of several plant species
(Ref. 91). Heterologous encapsidation was also shown to occur in
potyviruses. An isolate of zucchini yellow mosaic virus (ZYMV) that is
normally non-aphid transmissible due to a transmission-deficient coat
protein was found to be transmitted by the aphid vector due to
heterologous encapsidation when in a mixed infection with another
potyvirus, papaya ringspot virus (Ref. 92). Heterologous encapsidation
is essential for movement of some viruses. For example, umbraviruses do
not encode a coat protein, and therefore transmission between plants
occurs through encapsidation by an aphid-transmissible luteovirus coat
protein (Ref. 93).
    Heterologous encapsidation is considered a possible environmental
concern associated with PVCP-PIPs because of the potential that if a
virus is heterologously encapsidated by a PVC-protein, the viral genome
might be able to spread to plants the virus ordinarily had no means of
reaching and thus could not have infected. Experimental studies have
shown that some PVC-proteins in transgenic plants have the ability to
encapsidate even unrelated infecting viruses (Refs. 94, 95, 96, and
97). However, heterologous encapsidation involving a viral transgene
can only occur if an expressed coat protein possesses the appropriate
physical parameters to encapsidate the viral genome of infecting
viruses. When transgenic plants containing a PVCP-PIP display
resistance with very low or no levels of PVC-protein expression (e.g.,
due to PTGS), the probability of heterologous encapsidation would be
very small or non-existent. (For a more detailed discussion of PTGS and
suppression of gene silencing, see Unit II.E. above and Unit IV.F. of
the companion document also appearing in today's Federal Register.)
    Environmental concerns associated with heterologous encapsidation
when PVC-protein is expressed appear to be largely mitigated by several
factors. One, the heterologously encapsidated viral genome may not be
able to replicate in the new host plant and could therefore not
actually infect it. In addition, if replication is possible in the new
plant, the replicating viral genome encodes for and thus would produce
its own coat protein rather than that which heterologously encapsidated
it. This virus would not be transmitted by the new vector that brought
the heterologously encapsidated genome to the new host plant. The
epidemiological consequences of such heterologous encapsidation would
thus be limited. Another consideration for some viruses is that
effective vector transmission may depend on more than the coat protein
(Refs. 98 and 99), requiring regions of the viral genome not included
in PVCP-PIPs as defined for this proposal, e.g., coat protein read-
through domains or helper factors. Thus, in such cases, the coat
protein that could potentially heterologously encapsidate another viral
genome would not contain all the parts necessary to lead to a change in
vector specificity. In addition, in large monocultures of crop plants,
a vector is most likely to move from plant to plant within the field
and to transmit even a heterologously encapsidated viral genome to a
plant that the virus is already able to infect (Ref. 98). Finally, as
with recombination, as long as the PVC-protein expressed in the
transgenic plant is from a virus that normally infects the plant in the
area where it is planted, the outcome of any heterologous encapsidation
that may occur is expected to be the same in transgenic plants as in
natural, mixed infections.
    In addition to these considerations, EPA evaluated whether a virus
that is heterologously encapsidated and carried to a new host plant
might be exposed to a vector that feeds on the new host plant and
perhaps other plants the virus ordinarily could not access. EPA
considered whether this new vector might in some cases be able to
transmit the virus even though the virus would now be encapsidated in
its own coat protein, thereby expanding the virus' vector range. A new
vector could

possibly transfer the virus to new host plants, thus expanding the
plant host range as well (Ref. 57). EPA considers expansion of host
range through heterologous encapsidation to be an extremely unlikely
outcome because such an outcome depends on each event in a series of
rare events occurring. Should the probability of occurrence of any one
event in this series be zero, the adverse event of an expanded host
range would not occur. In addition to the events enumerated above,
additional events must also occur. First, a virus must be
heterologously encapsidated, an event that is possible only for some
viral genome-coat protein combinations. Second, a new vector must
transmit the encapsidated viral genome. Third, the transmission must be
to a new host plant. Fourth, the heterologously encapsidated viral
genome must be able to replicate in the new host plant. Fifth, the
resulting virus, now encapsidated in its own coat protein, must be
exposed to a new vector the virus never encountered before that is
nevertheless able to transmit it. Finally, this vector must transmit
the virus to a new plant that the virus' prior vectors never visited.
For such a series of events to be novel, the viruses, vectors, and
plants involved must have had no previous opportunity to interact, and
it is rare for such a condition to be met. For example, it is known
that many viruses are transmitted by polyphagous insects, which would
have already allowed the viruses to be introduced to many potential
plant species even in the absence of heterologous encapsidation (Ref.
57). Moreover, viruses may be transmitted at low frequency by a range
of species other than their primary vector or mechanically, e.g.,
through the practices of modern agriculture (Ref. 98).
    Another scenario EPA considered is one where a high enough
frequency of vector transmission to a new host plant due to
heterologous encapsidation might mean that secondary spread among new
plant hosts might not be required for the phenomenon to affect the
population, assuming that the virus is able to decrease the new host
plant's growth and/or reproduction. Although this scenario may be more
likely to occur than an expansion of host range given that fewer rare
events would have to occur, any impact on the affected plant population
would be highly localized being confined to plants in or near
transgenic crop fields. Such negative impacts are unlikely to be
sufficiently detrimental to require FIFRA regulation given their
localized nature and the probability that common agricultural practices
(e.g., vector control) could be used to manage the problem. Moreover,
although isolated instances of transmission may occur, a significant
proportion of a plant population is unlikely to be infected in such a
scenario. For example, a field experiment (discussed in Unit
III.D.1.iv.) showed that heterologous encapsidation led to infection of
only 2% of plants compared to 99% of plants infected under similar
conditions by a virus that is not heterologously encapsidated (Ref.
100). Most importantly, the heterologously encapsidated virus will
still have no way to spread among or beyond the plants of the affected
population. In the case where a plant population contains relatively
few individuals such that the impact of single plant infections would
be magnified, plant infections are even less likely to occur because in
addition to the inefficient nature of heterologous encapsidation, the
vector would be more likely to feed on the more abundant transgenic
crop plants. In some cases a vector may have a strong preference for a
specific plant over even closely related plants (Ref. 101).
    Finally, EPA evaluated whether after expansion to a new host, rapid
selection of variants best adapted to the new environment might lead to
the evolution of a new virus (Ref. 57). However, in addition to
requiring several of the rare events discussed above to occur, this
phenomenon is unlikely to be entirely novel in any circumstance. All
viruses that are occasionally heterologously encapsidated and
transmitted to a new plant host have had the opportunity to adapt to
new plant environments. The opportunities for rapid viral evolution
presented by transgenic plants containing PVCP-PIPs would not be
fundamentally different from what occurs in nature under reasonably
likely circumstances. Rapid viral evolution after heterologous
encapsidation is not dependent on the unique combination of viruses
that interact but rather the introduction of a virus to a new plant
host, an event that likely occurs in nature at some frequency for most
viruses either through heterologous encapsidation or through occasional
transmission that occurs mechanically or from secondary vectors (Ref.
98).
    iii. Synergy. In synergy, another type of viral interaction, the
disease severity of two viruses infecting together is greater than
expected based on the additive severity of each virus alone. For
example, when a plant containing potato virus X (PVX) is coinfected
with any of a number of potyviruses including tobacco vein mottling
virus, tobacco etch virus, and pepper mottle virus, the disease
symptoms are considerably worsened and PVX accumulates to a greater
concentration (Ref. 102). A listing of reported viral synergisms has
been compiled (Ref. 103).
    In developing this proposal, EPA addressed whether synergy could
occur between an infecting virus and a PVCP-PIP, thereby increasing the
severity of the infecting virus and whether any consequences for the
environment could result from such an increase. For disease severity to
worsen, the PVC-protein must be at least one of the factors causing
synergy. However, the coat protein is considered much less likely to be
responsible for synergism than other parts of the virus (Refs. 104 and
105), and a PVCP-PIP producing other viral proteins would not qualify
for this proposed exemption. In addition, any negative effects are
expected to manifest primarily in the transgenic crop itself.
Furthermore, any negative effects are expected to be self-limiting
because any plants containing a PVCP-PIP that is prone to display
synergy with viruses common in the areas of planting would be quickly
abandoned once such effects were detected, perhaps as early as the
field-testing stage of product development. Synergistic interactions
can be evaluated in transgenic plants before deployment by experimental
inoculation with all of the viruses likely to be encountered in the
field (Ref. 98). Developers have a strong incentive to undertake such
efforts to ensure the efficacy of their product after deployment.
    iv. Field experiments. The experiments referenced in Units
III.E.2.i. through iii. above investigated potential viral interactions
in transgenic plants containing a PVCP-PIP under laboratory conditions.
However, equally important is consideration of the likelihood and
potential impact of viral interactions under natural field conditions
(Ref. 106). Relatively few field studies have been conducted to address
the questions EPA is evaluating for this proposal, but the Agency has
carefully considered the available literature in developing this
proposed exemption.
    A 6-year experiment searched for and failed to find evidence of
interactions involving viral transgenes in 25,000 transgenic potato
plants transformed with various PLRV coat protein constructs. Plants
were exposed to infection by PLRV by direct inoculation, plant-to-plant
spread, or natural exposure. In field experiments, plants were also
naturally exposed to the complex of viruses that occur in the region.
Both the greenhouse and field tests failed to show any change in the

type or severity of disease symptoms, and all viruses isolated were
previously known to infect the plants and had the expected transmission
characteristics (Ref. 107). These results suggest that viral
interactions leading to evolution of new viruses and/or more severe
viral disease are events too rare to be detected in a field trial of
this size and duration.
    A 2-year experiment with transgenic melon and squash expressing
coat protein genes of an aphid-transmissible strain of CMV failed to
yield evidence that either recombination or heterologous encapsidation
enabled spread of an aphid non-transmissible strain of CMV in the field
(Ref. 108). A similar experiment used transgenic squash expressing coat
protein genes of an aphid-transmissible strain of watermelon mosaic
virus (WMV). Plants were mechanically inoculated with an aphid non-
transmissible strain of ZYMV, and subsequent transmissions of the virus
(assumed to be vectored by aphids) were assessed. Infections of ZYMV
were not detected in nontransgenic fields, but the virus infected up to
2% of plants in transgenic fields. Several lines of evidence suggested
ZYMV infection was mediated by the WMV PVC-protein heterologously
encapsidating the ZYMV viral genome. However, the virus spread over
short distances, and transmission at a low rate failed to lead to an
epidemic of ZYMV in fields of WMV-resistant transgenic squash despite
the presence of optimal conditions for transmission (Ref. 100). These
results support the contention that even if heterologous encapsidation
involving a PVC-protein were to occur, the impact is likely to be
negligible because each plant infection by a heterologously
encapsidated virus requires a series of rare events to occur. Viral
infection by normal routes of transmission can be at least an order of
magnitude more efficient and lead to relatively greater impacts (Ref.
100).
    An experiment to assess the biological and genetic diversity of
California CMV isolates sampled before and after deployment of
transgenic melon containing the CMV coat protein gene documented only
one CMV isolate that had significant sequence changes. However, the
same change was seen with infection of non-transgenic plants,
suggesting that this isolate did not result from recombination between
the transgene and an infecting virus (Ref. 109). The only field
experiment to directly assess the effect of recombination in a
transgenic plant containing a PVCP-PIP found no detectable grapevine
fanleaf virus (GFLV) recombinants containing the inserted coat protein
sequence over the course of a 4-year study (Ref. 110). Test plants
consisted of nontransgenic scions grafted onto transgenic and
nontransgenic rootstocks that were exposed over 3 years to GFLV
infection at two locations. Analysis of challenging GFLV isolates
revealed no difference in the molecular variability among isolates from
190 transgenic and 157 nontransgenic plants, or from plants within (253
individuals) or outside (94 individuals) of the two test sites.
    2. Proposed exemption criterion. The information in Units
III.E.2.ii. through iv. suggests that heterologous encapsidation very
rarely leads to changes in virus epidemiology that could have any
large-scale impact and that synergy in plants containing PVCP-PIPs is
also unlikely to cause any widespread environmental harm. Consistent
with these observations, the 2004 SAP noted that ``except perhaps for a
very few cases, neither heterologous encapsidation nor synergy should
be considered to be of serious concern'' (Ref. 60). However, the Agency
believes that in all cases, concerns associated with these types of
viral interactions are likely to be limited in scope (for reasons
discussed in Units III.E.2.ii. through iii.) such that the
determination can be made that they pose low risk to human health and
the environment. EPA therefore concludes that PVCP-PIPs present low
risk with respect to heterologous encapsidation and synergy and that
PVCP-PIPs could be exempted without further qualification or
requirements to address these endpoints.
    However, EPA is not able to conclude at this time that all PVCP-
PIPs are low risk with respect to recombination (although see Unit VII
for a discussion of EPA's request for information that might allow the
Agency to reach such a conclusion). The Agency notes that the vast
majority of interactions between a viral transgene and an infecting
virus are expected to be no different from those that would occur in a
natural mixed infection of the respective viruses and would not cause
any adverse environmental effects beyond what could occur in the
absence of the PVCP-PIP. Nevertheless, the information discussed in
Unit III.D.1.i. suggests that recombination among viruses may lead to
rare instances of adverse changes in virus epidemiology and/or
pathogenicity, e.g., a host range expansion. Based on the available
information, EPA is not able to rule out that viable, recombinant
viruses containing a portion of a PVCP-PIP could arise in transgenic
plants and that in a small set of circumstances (discussed in Unit
III.D.2.i.) such recombinants could be unlike those that could arise
naturally. EPA agrees with the conclusions of the 2004 SAP that ``[i]n
contrast to heterologous encapsidation and synergy, at least in theory,
the impact of recombination could be much greater, since there is now
abundant bioinformatic evidence that recombination has indeed, as long
suspected, played a key role in the emergence of new viruses over
evolutionary time'' (Ref. 25). The 2005 SAP concurred with this
conclusion by noting that there ``are a few scenarios, however, in
which recombination may have an incrementally higher probability of
creating a virus with new properties. In conclusion, the Panel
recommended the need for the Agency to have criteria to assess the
level of risk'' (Ref. 11).
    The Agency notes that the 2005 SAP concluded that ``the likelihood
for `novel' interactions is very low, and the environmental concerns
that might result from using PVCP-PIPs in the United States... is lower
than that which occurs naturally from mixed virus infections'' (Ref.
11). In addition, ``it was repeatedly stated that the consequences of
any recombination event are minimal. This conclusion was based on the
fact that nearly every plant on the planet is harboring multiple virus
infections with both closely related and taxonomically distinct
viruses, with essentially no new viruses emerging with substantially
different properties and causing wide pandemics or undesirable
environmental effects'' (Ref. 11). In spite of such comments, EPA's
proposal contains Sec.  174.27(b) because of the overall context of the
Panel's response which articulated several factors (discussed in Unit
III.D.2.) that should be considered when evaluating recombination. EPA
believes Sec.  174.27(b) is consistent with these comments of the 2005
SAP because the Agency believes these comments apply only when
considering the whole set of PVCP-PIPs that are likely to be developed.
For the PVCP-PIPs that would only qualify for an exemption without the
limitations provided by Sec.  174.27(b), EPA does not believe the
Agency can conclude low risk with respect to recombination because the
2004 and 2005 SAPs have identified specific instances where this
general conclusion may not hold.
    The few field evaluations conducted (discussed in Unit III.D.1.iv.)
suggest that adverse environmental effects due to recombination in
transgenic plants containing PVCP-PIPs are unlikely to occur at least
on a small scale over a short time period. However, large acreages of
plants containing a PVCP-

PIP grown over many years may provide increased opportunity for rare
events to occur that are unlikely to be detected in experimental
studies (Ref. 104). In addition, none of the experimental systems
described above would be predicted to involve viruses that would
otherwise not be expected to interact in a mixed infection found in
nature. Given the limited amount of field data available, particularly
data relevant to the circumstances EPA has identified as being of
highest concern (i.e., those that could lead to novel interactions),
EPA is limiting the proposed exemption to those PVCP-PIPs for which
novel viral interactions are unlikely to occur. When EPA consulted the
2004 SAP about situations in which novel viral interactions might be a
concern, the Panel agreed ``that recombination is a concern when the
two contributing viruses have not previously had a chance to
recombine'' (Ref. 25).
    In addition to considering the potential for novel viral
interactions to occur, EPA also considered whether transgenic plants
containing PVCP-PIPs might have a changed frequency of viral
interactions. The frequency could decrease because the cellular
concentration of viral RNA transcripts expressed from transgenes may be
orders of magnitude lower than the concentration of viral RNA commonly
found in natural, mixed infections (Ref. 111), reducing the opportunity
for recombination. The concentration of infecting viral RNA from the
target virus would also be reduced considerably if the PVCP-PIP is
efficacious, particularly when the mechanism of resistance relies on
PTGS to remove viral RNA transcripts with homology to the transgene
(Ref. 112), thereby also reducing the opportunity for recombination.
However, the frequency of interactions could also increase given that
transgene RNA expressed from a constitutive promoter could be available
for interactions with infecting viruses in all cells of the plant at
all times - unlike RNA from a virus in a natural infection. When a
virus invades a cell, it often replicates and then moves to other cells
within the plant. The RNA remaining in the initially infected cell
becomes encapsidated and may no longer be available for interactions
with another invading virus (Ref. 113). When EPA presented this issue
to the 2004 SAP, the panel responded that ``no increase in heterologous
encapsidation should be anticipated in PVCP-PIP plants'' and ``the
Panel believed that in general recombination was more likely to occur
in transgenic plants than in non-bioengineered plants.'' Nevertheless,
the Panel agreed ``that the important questions are not the relative
likelihood for recombination to occur, but rather whether recombinants
in transgenic plants are different from those in non-transgenic plants
and whether they are viable'' (Ref. 25). Thus, EPA's proposal focuses
on situations in which novel recombination events could occur due to
the presence of a PVCP-PIP.
    i. Proposed categorical exemption criterion in Sec.  174.27(b)(1).
In developing the proposed categorical exemption for a subset of PVCP-
PIPs in which a developer could self-determine whether the criteria
were met, EPA sought to clearly identify those situations that pose low
risk with respect to viral interactions.
    A PVCP-PIP would meet the viral interactions criterion under Sec.
174.27(b)(1) if:
    (i) The viral pathotype used to create the PVCP-PIP has
naturally infected plants in the United States and naturally infects
plants of the same species as those containing the PVCP-PIP, or
    (ii) The genetic material that encodes the pesticidal substance
or leads to the production of the pesticidal substance is inserted
only in an inverted repeat orientation or lacking an initiation
codon for protein synthesis such that no PVC-protein is produced in
the plant.

    Recombination between the coat protein gene of the PVCP-PIP and
infecting viruses would be expected to be of little concern in certain
instances: when such recombination would involve segments of viruses
that are judged likely to have had the opportunity to recombine in a
natural, mixed infection (and therefore any recombinants produced are
unlikely to be novel), and when PTGS results in only small, cleaved
pieces of RNA being available for recombination. The former situation
would be met if the conditions of the criterion in proposed Sec.
174.27(b)(1)(i) are met. The latter situation would be met if the
conditions of the criterion in proposed Sec.  174.27(b)(1)(ii) are met.
EPA is proposing that no further data or information would be needed to
evaluate risks associated with recombination when Sec.  174.27(b)(1) is
satisfied under either Sec.  174.27(b)(1)(i) or Sec.  174.27(b)(1)(ii),
and therefore no Agency review would be necessary. The developer may
make this determination.
    If the viral pathotype used to construct the PVCP-PIP was isolated
in the United States from the same plant species as was engineered to
contain the PVCP-PIP, the PVCP-PIP would meet the proposed criterion in
Sec.  174.27(b)(1)(i). It should be noted that this proposed criterion
would be used in concert with the proposed protein production criterion
in Sec.  174.27(c) discussed below in Unit III.E.2., which ensures that
any modifications from the natural isolate encode a protein that is no
more than minimally modified from a natural virus coat protein. Thus,
any coat protein that satisfies Sec.  174.27(c) would be extremely
unlikely to confer significantly different properties on any virus that
could potentially acquire the coat protein through recombination with
the genetic material of the PVCP-PIP.
    The Agency asked the FIFRA SAP during the October 2004 meeting to
what extent PVCP-PIPs in plants might present a potential concern
should interactions with infecting viruses occur. The Panel expressed
concern only ``about certain limited situations'' and clarified that
``in most cases there is little a priori reason to believe that
recombinants between viruses and transgenes will be more of a problem
than recombinants between two viruses infecting the same plant, unless
transgenes are derived from severe or exotic isolates. The general
recommendation to use mild, endemic isolates as the source of the
transgene (e.g. Hammond et al. 1999) should minimize any potential for
creation of novel isolates that would not equally easily arise in
natural mixed infections'' (Refs. 25 and 57). The Agency's proposed
Sec.  174.27(b)(1)(i) is consistent with this 2004 SAP recommendation
because it excludes exotic virus isolates as the source of the PVCP-PIP
transgene. Although proposed Sec.  174.27(b)(1)(i) does not require
that the virus isolate be a ``mild'' form of the virus, it does ensure
that when virus isolates capable of causing severe cases of viral
disease are used, the PVCP-PIP may only meet Sec.  174.27(b)(1)(i) if
the viral pathotype was present in the natural system and therefore
should pose no risk of novel interactions.
    The 2005 SAP offered a decision flowchart indicating a point at
which the Agency should identify the few scenarios where recombination
may be of concern: ``the question arises as to whether recombination of
the sequence could lead to a significant change in the properties of
the recombinant over the original properties of the superinfecting
virus. Significant changes include increase in pathogenicity, increase
of host range or change of vector'' (Ref. 11). EPA believes that
consideration of whether the conditions of proposed Sec.
174.27(b)(1)(i) are met addresses whether the potential exists for
significant changes in the properties of a recombinant virus compared
to what

might occur in a natural, mixed infection.
    In addition to excluding exotic virus isolates, proposed Sec.
174.27(b)(1)(i) also excludes PVCP-PIPs that are inserted into a plant
species that is not naturally infected by the virus used to create the
PVCP-PIP. Most PVCP-PIPs are created from viruses that do naturally
infect the plant species into which they are inserted because greater
efficacy is achieved when a virus most similar to the target virus is
used as the source of the sequence used in the PVCP-PIP. However,
virus-resistant transgenic plants have been created where this is not
the case (Ref. 114). In these situations, a virus is introduced into a
system where it does not naturally occur, and viruses with which it
does not otherwise interact may be present in that system. The Agency
cannot a priori determine that such interactions are safe because there
is no experience upon which to base such a finding.
    Proposed Sec.  174.27(b)(1)(i) is also consistent with the 2005
SAP's recommendation to consider ``whether recombination of the
sequence could lead to a significant change in the properties of the
recombinant over the original properties of the superinfecting virus''
(Ref. 11). When the viral pathotype used to create the PVCP-PIP has
naturally infected plants in the United States and naturally infects
plants of the same species as those containing the PVCP-PIP, the
sequences that could interact would be expected to already have
opportunities to interact in nature and thus no novel recombinants
should be produced.
    The Agency's proposed Sec.  174.27(b)(1)(ii) is consistent with the
2005 SAP's recommendation to consider whether the PVCP-PIP expresses
PVC-protein when evaluating the potential consequences of recombination
(Ref. 11). When a PVCP-PIP expresses no PVC-protein because it is
designed to mediate resistance through PTGS, recombination would be of
little concern because ``recombination between a full-length viral RNA
and a cleaved small RNA resulting from PTGS would yield a truncated
non-functional RNA. Therefore, a PTGS transgene poses negligible
potential to yield novel recombinant viruses'' (Ref. 11). EPA therefore
makes part of its proposal two circumstances when, according to the
2005 SAP, the PVCP-PIP can only mediate resistance through PTGS because
it would produce no PVC-protein: when the genetic material that encodes
the pesticidal substance or leads to the production of the pesticidal
substance is inserted only in an inverted repeat orientation or lacking
an initiation codon for protein synthesis such that no PVC-protein is
produced in the plant (Ref. 11). See Unit III.D.2.ii. below for a
discussion of how other constructs mediating resistance through PTGS
could meet Sec.  174.27(b).
    One Panel member noted, ``PTGS results in small RNA from the PIP
and the infecting virus that could, in certain circumstances, be
recombinatorial.'' However, the Panel concluded ``this minimal RNA
would not confer a phenotype to the recombinant, would result in just a
few nucleotide changes in a potential recombinant, and thus would be
irrelevant'' (Ref. 11).
    EPA proposes to define the term ``naturally infect'' to mean ``to
infect by transmission to a plant through direct plant-to-plant contact
(e.g., pollen or seed), an inanimate object (e.g., farm machinery), or
vector (e.g., arthropod, nematode, or fungus). It does not include
infection by transmission that occurs only through intentional human
intervention, e.g., manual infection in a laboratory or greenhouse
setting.'' The Agency is proposing this definition specifically to
exclude transmission that occurs only through intentional human
intervention because such transmission would have little relevance to
normal virus infection. EPA recognizes that humans may play an
inadvertent role in infection (e.g., by transmitting the virus on farm
machinery). Such unintentional (and often unavoidable) transmission can
be an important means of virus transmission, leading to the natural
presence of viruses in plants. EPA therefore proposes to include this
mode of incidental transmission in the definition of naturally infect.
    EPA uses the term ``viral pathotype'' rather than the more generic
term ``virus'' in response to the October 2004 FIFRA SAP comment that
``[n]ot all isolates of a virus infect and cause disease in all plant
genotypes and, as a consequence, the unqualified use of the term
`virus' when setting a condition for applicants to the Agency [is] not
adequate in this context. It is therefore appropriate in the context of
biosafety as well as virus epidemiology to recognize the value of
defining specific viral pathotypes or host range variants.'' The 2005
SAP was asked to comment on the use of this term and responded, ``there
was not much discussion of this term. The Panel suggested that logic
says that local or indigenous virus isolates, or those with significant
sequence similarity, will be used to generate PVCP-PIPs. From what we
know now, only those viruses with high sequence identity will be useful
as sources of the PVCP-PIP transgene.'' EPA agrees that generally viral
pathotypes that meet Sec.  174.27(b)(1) will be those most effective
for creating PVCP-PIPs and will therefore be the most commonly used.
However, EPA considers the limitations imposed by this term to be
necessary because the Agency cannot conclude that viruses not meeting
this criterion would be low risk with respect to recombination.
    In this proposed criterion and in Sec.  174.27(c) discussed below,
EPA uses the phrase ``genetic material that encodes the pesticidal
substance or leads to the production of the pesticidal substance,''
rather than the phrase ``genetic material necessary for the
production,'' to indicate that regulatory regions, such as promoters,
enhancers, or terminators, need not be considered in evaluating whether
a PVCP-PIP satisfies these criteria. EPA is not proposing to amend the
definitions for ``genetic material necessary for the production'' or
``regulatory region,'' both found at 40 CFR 174.3, and is not seeking
any comment on these definitions.
    ii. Proposed exemption criterion conditional on Agency
determination in Sec.  174.27(b)(2). The Agency recognizes that many
PVCP-PIPs may pose low risk with respect to recombination even though
they fail to satisfy Sec.  174.27(b)(1). Therefore, EPA is proposing an
approach under which PVCP-PIPs that fail to meet Sec.  174.27(b)(1)
could still meet Sec.  174.27(b), subject to an Agency review to
determine whether they meet a different set of conditions related to
this issue. Under this proposed approach, a PVCP-PIP would meet Sec.
174.27(b) under Sec.  174.27(b)(2) if the Agency determines that
viruses that naturally infect the plant containing the PVCP-PIP are
unlikely to acquire the coat protein sequence through recombination and
produce a viable virus with significantly different properties than
either parent virus.
    The conditions in proposed Sec.  174.27(b)(1) address the potential
for recombinants to arise unlike those expected in natural mixed
infections primarily by ensuring that no novel viral interactions
occur. Under proposed Sec.  174.27(b)(2), a PVCP-PIP could qualify for
exemption even when novel viral interactions could occur providing
steps were taken to ensure that an infecting virus would not acquire a
portion of the PVCP-PIP coat protein sequence through recombination and
produce a viable virus with significantly different properties than
either parent virus.
    Experimental evidence has suggested a number of ways coat protein
genes of certain viruses may be modified in constructing a PVCP-PIP to
reduce the possibility they would participate in a

recombination event with an infecting virus. For example, removing the
3' untranslated region (UTR) in the coat protein mRNA transcript may be
effective at reducing recombination for viruses that carry the
initiation promoters of RNA replication in this region (Ref. 115).
Evidence suggests that recombination among RNA viruses occurs via
template switching by the viral replicase during replication such that
a hybrid molecule is formed (Ref. 116). Inclusion of the 3' UTR may
enable replication to begin on the mRNA transcript and then switch to
the RNA of the invading virus. Removal of this region would necessitate
two separate template-switching events to form a successful recombinant
and thus reduce its likelihood of occurrence (Ref. 80). Experiments
with CCMV demonstrated that deletions in the 3' UTR did indeed reduce
the recovery of recombinant viruses (Ref. 117). Since functional
resistance is still conferred by constructs containing a CP lacking the
3' UTR, this region may not be necessary. Other techniques that have
been suggested include:
     Reducing the extent of shared sequence similarity between
the infecting virus and the transgene to reduce the opportunities for
homologous recombination (Ref. 118).
     Excluding any sequences containing replicase recognition
sites that are potential sites of recombination and any sequences known
or thought to be recombination hotspots, e.g., promoters for genomic
and subgenomic RNA synthesis (Ref. 119).
     Avoiding potential hairpin structures in the transgene
that might function as acceptor structures for the replicase complex
(Ref. 120).
    It is important to note that any PVC-protein produced must be
evaluated under Sec.  174.27(c) in order for the PVCP-PIP to qualify
for exemption. Some techniques that may enable a PVCP-PIP to meet Sec.
174.27(b)(2) would preclude the PVCP-PIP from meeting Sec.
174.27(c)(1) and necessitate a review under Sec.  174.27(c)(2). For
example, a construct could meet proposed Sec.  174.27(b)(2) if it
contained portions of several different coat protein genes in tandem,
linked together in such a way that if the sequence were translated it
would yield a non-functional coat protein of no use to a virus. A virus
that acquired this entire sequence through recombination in exchange
for portions of its own genome would likely be nonviable. As another
example, a construct might meet proposed Sec.  174.27(b)(2) if it
contained a very small portion of a coat protein gene. In such cases, a
virus would be unlikely to acquire this sequence through recombination
without picking up additional pieces of genetic material from the
construct or the plant genome that would likely render the virus
nonviable. Or, if a virus did acquire a piece of just the small part of
the coat protein sequence contained in the transgenic plant, it would
likely not be large enough to significantly change the properties of
the parent virus. Any PVC-protein produced from either such construct
would fail to meet Sec.  174.27(c)(1) but could be evaluated under and
may nevertheless meet Sec.  174.27(c)(2) (see Unit III.E.2. below).
    EPA recognizes the comments of the 2004 SAP that ``methods for
minimizing recombination are only partially effective. For this reason,
the question remains whether novel recombinants would be created in
transgenic plants, and simply reducing the frequency of these events is
not an answer to the question'' (Ref. 60). However, EPA believes that a
combination of two or more methods, or even perhaps a single method in
some cases, could be employed to reduce the expected frequency of
recombination such that the Agency would be able to make a
determination that a PVCP-PIP would pose low risk with respect to viral
interactions. EPA asked the 2004 SAP ``which methods are sufficiently
effective such that requiring measurement of recombination rates would
be unnecessary. The Panel doubted if the... methods [discussed] are
sufficiently effective to warrant the reduction of recombination rates
below the level that the actual measurement will be unnecessary'' (Ref.
25). However, the Agency would have the opportunity during the case-by-
case Agency review under Sec.  174.27(b)(2) to consider the particular
viral system and whether literature supports the contention that the
recombination reduction techniques are likely to be sufficiently
effective in the system in which they are employed. EPA anticipates
that the Agency could base this determination on the expected reduction
in frequency of recombination as determined from the literature and
that actual measurement of recombination rates may be unnecessary.
Given that there is no universally applicable method for reducing
recombination frequency and this type of case-by-case consideration of
the particular virus system in question must be conducted, EPA believes
an Agency review is needed to make this determination. With an Agency
determination under Sec.  174.27(b)(2), EPA would create a criterion
that would encompass a larger set of those PVCP-PIPs that pose low risk
with respect to viral interactions than are covered under Sec.
174.27(b)(1).
    Section 174.27(b)(2) is consistent with the advice of the 2005 SAP
in that it incorporates the portions of the proposed decision tree that
allow consideration of whether there are ``features controlling
recombination,'' whether ``the protein [is] complete,'' and whether the
plant host contains ``genes that reduce recombination'' (Ref. 11).
Likewise, the review procedures for determining whether a PVCP-PIP met
the conditions of Sec.  174.27(b)(2) would also be able to consider
``the type of RNA-dependent RNA polymerase (RdRps) encoded by the
superinfecting virus and the compartmentalization of its site of
replication'' as suggested by the 2005 SAP (Ref. 11). Although EPA
notes that there was some disagreement among the Panel members about
the appropriateness of including such information as part of the flow
chart, the Agency believes that this information could be reasonably
considered when available and when sufficient knowledge about the
plant/virus system exists such that it would offer useful information
for evaluating this criterion. Overall, Sec.  174.27(b) thus enables
the Agency to consider either under Sec.  174.27(b)(1) or Sec.
174.27(b)(2) all of the factors mentioned in the flowchart by the 2005
SAP.
    3. Historical approaches still under consideration. EPA's proposed
exemption in 1994 did not contain any criteria related to viral
interactions. However, since that time, many additional scientific
papers and reviews have been published on this topic. Most affirm the
general safety of PVCP-PIPs with respect to viral interactions, but
some call into question assumptions of how generically this conclusion
holds across all PVCP-PIPs. For example, although the 2000 NRC report
stated that ``[m]ost virus-derived resistance genes are unlikely to
present unusual or unmanageable problems that differ from those
associated with traditional breeding for virus resistance,'' the NRC's
report also suggested that their conclusions were based on the
assumption that certain risk management strategies should or would be
implemented, e.g., elimination of specific sequences to limit the
potential for recombination (Ref. 10). EPA believes the Agency's 1994
conclusion of low probability of risk still holds for most PVCP-PIPs.
However, in order to grant an exemption under FIFRA, EPA must be able
to make such a finding for all PVCP-PIPs covered by the exemption and
must make its safety determination

in the absence of any regulatory oversight under FIFRA that could
ensure mitigation measures, such as those discussed in the NRC report,
were employed. Therefore, it appears prudent at this time to limit this
proposed exemption with a criterion that restricts the potential for
novel recombination events, as these have been identified as the rare
situation in which viral interactions in plants containing a PVCP-PIP
may lead to adverse environmental effects.
    EPA presented a set of conditions to the 2004 SAP and asked whether
they would significantly reduce either the novelty or frequency of
viral interactions in plants containing PVCP-PIPs such that the Agency
would not need to regulate the PVCP-PIP (Ref. 25). The first proposed
condition was that ``the genetic material of the PVCP-PIP is translated
and/or transcribed in the same cells, tissues, and developmental stages
naturally infected by every virus from which any segment of a coat
protein gene used in the PVCP-PIP was derived.'' EPA considered such a
condition because with a PVCP-PIP, plants may express viral genes in
cells and/or tissues that the virus does not normally infect. Genetic
promoters currently used in most transgenic plants cause constitutive
expression of transgenes at developmental stages that might otherwise
be unaffected by viral infection and often in tissues that the virus
does not normally infect (Ref. 113). For example, luteoviruses are
normally expressed only in phloem tissue, but the cauliflower mosaic
virus (CaMV) promoter, commonly found in existing PIP constructs, would
drive expression of luteoviral coat protein in all plant cells. Some
evidence suggests that in natural infections different viruses have
different temporal or spatial expression patterns that would limit
their interactions (Refs. 63, 121, and 122). However, the 2004 SAP
concluded that such a condition would be of limited utility because
``[m]ost plant viruses are present in a wide range of cell and tissue
types'' (Ref. 25).
    The second condition proposed to the 2004 SAP was that ``the
genetic material of the PVCP-PIP contains coat protein genes or
segments of coat protein genes from viruses established throughout the
regions where the crop is planted in the United States and that
naturally infect the crop into which the genes have been inserted.''
EPA considered the first part of this criterion because plants may be
engineered with coat protein genes from an exotic strain of a virus
that may be more virulent or have other properties different from
endemic isolates. Interactions between a PVCP-PIP based on such virus
sequences and infecting viruses could potentially change the
epidemiology or pathogenicity of the infecting viruses. The 2004 SAP
concurred that ``using such an exotic coat protein gene would open
possibilities for novel interactions.'' EPA's current proposed Sec.
174.27(b) thus excludes from exemption PVCP-PIPs based on coat protein
genes from exotic viruses unless steps have been taken to reduce the
frequency of recombination.
    EPA considered the second part of this 2004 criterion (i.e., the
genetic material of the PVCP-PIP contains coat protein genes or
segments of coat protein genes from viruses... that naturally infect
the crop into which the genes have been inserted) because in
heterologous resistance a plant may be resistant to infection by a
particular virus in spite of having the coat protein gene of another
virus incorporated into its genome. For example, coat protein genes
from LMV were used to provide resistance to PVY in tobacco which is not
infected by LMV (Ref. 114). In such plants, LMV sequences might have a
new opportunity to interact with viruses that infect tobacco. The 2004
Panel concluded that ``[w]hat is described here is most often
implemented: in designing a PVCP transgene, better efficacy is often
observed if it is as similar as possible to the target virus.''
Nevertheless, EPA believes that EPA's current proposed criterion (b) is
appropriate given that PVCP-PIPs may be developed using heterologous
resistance. This criterion excludes from exemption PVCP-PIPs used in
plants that the virus used to create the PVCP-PIP does not naturally
infect unless steps have been taken to reduce the frequency of
recombination.
    The third condition proposed to the 2004 SAP was that ``the PVCP-
PIP has been modified by a method scientifically documented to minimize
recombination (e.g., deletion of the 3' untranslated region of the coat
protein gene). As discussed above, the 2004 SAP expressed reservation
about such a criterion, and EPA recognizes that any single method for
minimizing recombination may be only partially effective (Ref. 60).
However, EPA believes that a combination of two or more methods, or
even perhaps a single method in some cases, could be employed such that
the expected frequency of recombination would be reduced to a level
that would support determination that a PVCP-PIP would pose low risk
with respect to viral interactions, but that such a determination could
only be made on a case-by-case basis. EPA thus intends that the
proposed criterion in Sec.  174.27(b)(2)(ii) would allow the Agency to
make this determination after review.
    The fourth condition proposed to the 2004 SAP was that ``the PVCP-
PIP has been modified by a method scientifically documented to minimize
heterologous encapsidation or vector transmission, or there is minimal
potential for heterologous encapsidation because no protein from the
introduced PVCP-PIP is produced in the transgenic plant or the virus
does not participate in heterologous encapsidation in nature.'' The
2004 SAP concluded that ``[t]his method can... be considered seriously
if deemed necessary'' (Ref. 25). However, the Agency concluded (as
discussed above in Unit III.D.1.ii.) that such methods are not
necessary because heterologous encapsidation is so rarely likely to be
of any significant ecological concern.
    Based on these considerations, EPA presented a set of modified
conditions to the 2005 SAP that reflected the advice of the 2004 SAP.
Those conditions were the same as those that EPA is proposing today in
Sec.  174.27(b) except that Sec.  174.27(b)(2) as submitted to the 2005
SAP included an additional provision: this criterion could be met by
meeting the current conditions or by meeting the condition that ``the
properties of the viral pathotype that are determined by the coat
protein gene used to create the PVCP-PIP are substantially similar to
the properties of a viral pathotype that naturally infects plants in
the United States, and the viral pathotype used to create the PVCP-PIP
naturally infects plants of the same species as that containing the
PVCP-PIP.'' EPA is no longer proposing this condition as a means of
meeting Sec.  174.27(b) because the 2005 SAP concluded that it was
``unusable and cannot be re-written into a satisfactory form'' because
of the difficulty of defining ``properties'' and ``substantially
similar'' in this context (Ref. 11).

E. Production of Proteins

    1. Scientific issues. In addition to weediness and viral
interactions, a third concern associated with PVCP-PIPs relates to the
potential production of proteins (called PVC-proteins) from the plant
virus coat protein sequences of the PVCP-PIP, i.e., the potential for
human or nontarget organism exposure to proteins that have not
previously existed in nature and thus should be examined to determine
whether they have potentially toxic or allergenic properties. EPA must
consider the safety of any potentially expressed proteins that are part
of the PIP when proposing

criteria to evaluate PVCP-PIPs for possible exemption.
    EPA considered human dietary, human occupational, and nontarget
exposure risks in evaluating the safety of PVC-proteins for purposes of
this proposal as the Agency must do when evaluating whether a pesticide
can be exempt from the requirements of FIFRA. See EPA's assessment of
human dietary exposure risks and other non-occupational exposure risks
published in the companion document in today's Federal Register that
proposes to establish a tolerance exemption under FFDCA section 408 for
residues of the PVC-protein portion of a PVCP-PIP.
    Many, if not all, of the considerations used to evaluate the
potential for novel occupational or nontarget exposures can be directly
extrapolated from the discussion in this companion document describing
EPA's base of experience with viruses infecting food plants. That
analysis led the Agency to draw three conclusions on which it is
relying to support the proposed tolerance exemption for residues of
PVC-proteins in food and which can also be used to support this
proposed criterion for exemption from FIFRA requirements. First, virus-
infected plants have always been a part of the human and domestic
animal food supply. Most crops are frequently infected with plant
viruses, and food from these crops has been and is being consumed
without adverse human or animal health effects. Second, plant viruses
are not infectious to humans, including children and infants, or to
other mammals. Third, plant virus coat proteins, while widespread in
food, have not been associated with toxic or allergenic effects to
animals or humans. EPA derived these conclusions from a sufficient
experience and information base to support the proposed tolerance
exemption and this proposed criterion for exemption from FIFRA
requirements.
    EPA consulted the 2004 SAP about possible nontarget effects of PVC-
proteins and the validity of the Agency's risk assessment being based
on the known history of safe exposure to coat proteins of naturally
occurring plant viruses. Virus infected plants have always been a part
of the natural environment, and organisms that interact with plants
have likely been exposed to plant virus coat proteins over long periods
of time. The panel confirmed that PVC-proteins within the range of
natural variation of the virus would not be anticipated to present
risks to nontarget organisms, concluding that, ``[l]ethal effects in
animal life after feeding on PVCP-PIP plants are highly unlikely
because plant viruses are not known to have deleterious effects on
animal life. Additionally, animals routinely feed on non-engineered
virus-infected plants and do not die.... [S]ublethal effects are not
expected to be manifested in animal life, again because wildlife and
insects regularly feed on non-engineered virus-infected plants with no
apparent sublethal damage'' (Ref. 60).
    The 2005 SAP echoed these general conclusions by pointing out that
virus coat proteins ``are naturally present in the environment and no
adverse effects to humans or non-targets have been reported'' (Ref.
11). However, the 2005 SAP also suggested that additional concerns
might warrant evaluation, including ``indirect ecological effects (such
as altered food sources, vegetative cover, or microbial communities)''
(Ref. 11). The particular concerns associated with such effects were
not articulated. PVC-proteins that meet the conditions of this
exemption are not expected to alter nontarget food sources because they
would be so similar to plant virus coat proteins that occur naturally.
Indirect effects such as changes in vegetative cover might occur if
crop plants containing a PVCP-PIP are larger and/or more productive in
the absence of virus infection relative to plants that are infected.
However, the overall effect on nontarget organisms is still likely to
be minor given that crops are often grown in the absence of viral
disease even without the use of a PVCP-PIP, and PVCP-PIPs exempted by
this proposal would have very limited ability to spread from crop
plants to wild or weedy relatives. PVCP-PIPs are not expected to impact
microbial communities because natural plant virus coat proteins are not
known to have any toxic mode of action. Moreover, plant virus coat
proteins already occur naturally in the environment so microbial
communities are already exposed to such proteins. Some Panel members
also ``expressed concern over potential effects on pollinators,'' but
EPA is unaware of any scientific evidence supporting this concern. EPA
concurs with other Panel members who believed that ``a history of
exposure by pollinators to naturally infected plants can be taken as
indicating that there are no novel risks'' (Ref. 11).
    Other concerns raised by the 2005 SAP regarding nontarget and human
non-dietary exposure are addressed in the companion document published
in today's Federal Register, where they are discussed in the context of
consideration of the human dietary risks associated with PVC-proteins.
The companion document describes in Unit IV.C., for example, the basis
for EPA's conclusion that the hazard associated with PVC-proteins that
meet Sec.  174.27(c) of this proposed exemption is sufficiently low
that they do not rise to the level warranting regulation. These same
arguments can be applied to PVC-proteins that meet Sec.  174.27(c) in
this proposal, even in the rare cases when nontarget exposure to a PVC-
protein might be greater than the exposure to the corresponding natural
plant virus coat protein. The companion document also describes in Unit
IV.C. rationales that can be used to support EPA's conclusion that
nontarget exposure to PVC-proteins in plant tissues that do not
normally contain the corresponding plant virus coat protein is unlikely
to contribute significantly to risk. Nontarget organisms would be
exposed to natural plant virus coat proteins through a variety of
routes and there is no evidence that they would be toxic to any
nontarget organisms regardless of the route of exposure.
    2. Proposed exemption criterion. As with the other proposed
criteria discussed in this document, EPA is proposing that Sec.
174.27(c) would have two parts: Section 174.27(c)(1) under which a
developer may self-determine if a PVCP-PIP meets the conditions, and
Sec.  174.27(c)(2) under which the Agency must make the determination.
    i. Proposed categorical exemption criterion in Sec.  174.27(c)(1).
In developing the proposed categorical exemption for a subset of PVCP-
PIPs in which a developer could self-determine whether the criteria
were met, EPA sought to identify clearly those situations that pose low
risk with respect to protein production because any PVC-proteins
produced would be within the range of natural variation. EPA wants to
ensure that a long history of safe human and nontarget exposure has
occurred for any PVC-protein produced from a PVCP-PIP that could
qualify for this exemption. A PVCP-PIP would meet Sec.  174.27(c)(1) if
a product developer self-determines that:
    The genetic material that encodes the pesticidal substance or
leads to the production of the pesticidal substance:
    (i) Is inserted only in an inverted repeat orientation or
lacking an initiation codon for protein synthesis such that no PVC-
protein is produced in the plant, or
    (ii) Encodes only a single virtually unmodified viral coat
protein. Multiple PVC-proteins could each separately meet this
criterion. Chimeric PVC-proteins do not qualify.

    EPA intends with the phrase ``is inserted only in an inverted
repeat orientation or lacking an initiation codon for protein synthesis
such that no PVC-protein is produced in the plant''

to include only those PVCP-PIPs with the specified types of constructs
that the 2005 SAP indicated provide a high degree of certainty that no
PVC-protein would be produced. Although other types of constructs may
also usually not produce any PVC-protein, EPA believes it is necessary
to incorporate into its proposal a provision for an Agency review of
such constructs. In such a review, EPA could evaluate the level of
protein production, if any, that could occur under a variety of
circumstances and environmental conditions representative of those that
the plant may experience (see Unit III.E.2.ii.). EPA includes the word
``only'' and the phrase ``such that no PVC-protein is produced in the
plant'' in Sec.  174.27(c)(1)(i) to ensure that the proposed exemption
encompasses only those PVCP-PIPs that the 2005 SAP indicated ``could be
safely determined to have no [PVC-protein] expression regardless of
plant tissue, developmental stage, environmental conditions, or
exposure to virally-encoded suppressors of PTGS'' (Ref. 11). The
proposed exemption criterion in Sec.  174.27(c)(1)(i) would not be met
by a PVCP-PIP when there are multiple-copy insertions in the plant if
any of the copies is not in an inverted repeat orientation or lacking
an initiation codon for protein synthesis.
    The Agency proposes to define the term ``unmodified'' to mean,
``having or coding for an amino acid sequence that is identical to an
entire coat protein of a naturally occurring plant virus. The Agency
proposes to define the term ``virtually unmodified'' to mean, ``having
or coding for an amino acid sequence that is identical to an entire
coat protein of a naturally occurring plant virus, except for the
addition of one or two amino acids at the N- and/or C-terminus other
than cysteine, asparagine, serine, and threonine and/or the deletion of
one or two amino acids at the N- and/or C-terminus.'' EPA's rationale
for these proposed definitions and alternative proposals for defining
``virtually unmodified'' are found in the companion document published
in today's Federal Register. The alternative proposals for virtually
unmodified will also be considered as alternatives under this FIFRA
proposal.
    EPA is proposing to exclude more significantly modified PVC-
proteins from the proposed categorical exemption by requiring that the
genetic material encode ``only a single virtually unmodified viral coat
protein.'' For example, PVC-proteins containing internal insertions,
deletions, or amino acid substitutions would be excluded, as would be
chimeric proteins that are encoded by a sequence constructed from
portions of two or more different plant virus coat protein genes. EPA
is proposing to exclude such PVC-proteins from the self-determining
part of the exemption in response to the advice of the FIFRA SAP in
October 2004 that, ``[t]here was general agreement that an
allergenicity assessment\2\ would be appropriate for insertions or
deletions, except perhaps for terminal deletions that do not affect
overall protein structure.'' Insufficient information exists at this
time to allow EPA to describe a priori a criterion that would ensure
all PVC-proteins with modifications other than those encompassed by the
definition of ``virtually unmodified'' fall within the base of
experience supporting the proposed exemption. At this time, it is not
possible to make a categorical risk assessment finding that other types
of changes are unlikely to change the characteristics of any protein
produced. Thus, EPA proposes no other modifications be allowed in PVC-
proteins that would meet Sec.  174.27(c)(1).
---------------------------------------------------------------------------

    \2\ The concern relating to the need for an allergenicity
assessment is relevant to the Agency's determinations concerning
occupational exposures.
---------------------------------------------------------------------------

    EPA intends that multiple PVC-proteins expressed in the same plant
could each separately meet the criterion in Sec.  174.27(c)(1)(ii) but
that chimeric PVC-proteins could not meet this criterion. Chimeric
proteins would include PVC-proteins composed of the fusion of two (or
more) whole or partial capsid proteins, as well as chimeric proteins
that contain a PVC-protein fused with another, unrelated protein. The
2005 SAP concluded that such chimeric proteins could possibly have
``completely different antigenic and possibly allergenic properties
compared to the properties of the individual capsid proteins'' (Ref.
11). EPA is therefore unable to conclude that such proteins would be
low risk without a case-by-case review of the protein. EPA intends that
multiple, distinct PVC-proteins produced, for example, from a single
transgene insertion event or from multiple insertion events in the same
plant, could qualify for this exemption because the Agency believes
that the properties of each individual protein would be the relevant
factors to consider. Some members of the 2005 SAP believed that ``EPA
evaluations should consider effects of multiple constructs of PVCP-PIPs
introduced in transgenic plants'' (Ref. 11). The rationale for this
concern appears based in part on the potential for a synergistic effect
from multiple toxins. However, PVC-proteins produced from a PVCP-PIP
that could qualify for this exemption would not be expected to have any
toxic mode of action that could cause such a phenomenon. The rationale
for this concern appears to be also based in part on the potential for
multiple PVC-proteins to ``alter `natural' protein production in
plants'' (Ref. 11). However, EPA concurs with other 2005 SAP members
who ``believed that this situation was no different than is likely to
occur in nature, where a plant might be infected by multiple unrelated
viruses'' (Ref. 11). (See also Unit IV.E.1. in the companion document
published in today's Federal Register for the basis for EPA's
conclusion that exposure to plants with different levels of proteins
elicited by pathogen attack, wounding, or stress, i.e., ``pathogenesis-
related proteins,'' likely occurs normally.)
    EPA believes the phrase ``an entire coat protein'' in the
definition of ``virtually unmodified'' conveys that segments of PVC-
proteins do not meet the criterion in Sec.  174.27(c)(1)(ii). This
limitation is based on the advice of the 2005 SAP that ``[d]etermining
whether PVC-proteins containing terminal deletions, or any other
modifications, are within the range of natural variation would require
the development of a database of the natural variation and truncated
forms of PVC-proteins that occur naturally.'' As such, EPA could more
appropriately take this consideration into account under the criterion
in Sec.  174.27(c)(2)(i) which contains provisions for an Agency review
(discussed below in Unit III.E.2.ii.). However, EPA is considering
several alternative definitions for ``virtually unmodified,'' some of
which may allow truncated PVC-proteins to meet the proposed criterion
in Sec.  174.27(c)(1)(ii). These alternatives are presented and
discussed in Unit IV.E.1. of the companion document published elsewhere
in today's Federal Register.
    If the genetic material that encodes the pesticidal substance or
leads to the production of the pesticidal substance encodes only a
single virtually unmodified viral coat protein, no novel exposures to
humans or nontarget organisms are likely to occur because these PVC-
proteins are essentially identical to plant viral coat proteins that
are widespread in the plant kingdom, as most plants are susceptible to
infection by one or more viruses. EPA is relying on this history of
safe exposure to support this proposal. The Agency believes that when
such a PVCP-PIP is used, the PVCP-PIP would pose low probability of
risk with respect to protein production. EPA is proposing that no
further data or information would be needed to evaluate this issue

when Sec.  174.27(c)(1) is satisfied, and therefore no Agency review
would be necessary.
    ii. Proposed exemption criterion conditional on Agency
determination in Sec.  174.27(c)(2). The Agency acknowledges that many
PVCP-PIPs may pose low risk with respect to concerns associated with
protein production even though they fail to satisfy Sec.  174.27(c)(1).
EPA is proposing to review such PVCP-PIPs under slightly different
factors that the Agency believes also ensure that qualifying PVCP-PIPs
pose low risk with respect to concerns associated with protein
production. Therefore, EPA is proposing that, under Sec.  174.27(c)(2),
a PVCP-PIP would also meet Sec.  174.27(c) if:
    The Agency determines after review that the genetic material
that encodes the pesticidal substance or leads to the production of
the pesticidal substance:
    (i) Encodes a protein that is minimally modified from a coat
protein from a virus that naturally infects plants, or
    (ii) Produces no protein.
    EPA developed the criterion in Sec.  174.27(c)(2) because the
Agency recognizes that developers may wish to modify PVCP-PIP
constructs to achieve certain product development goals such as greater
efficacy, and such modifications might result in changes to the
protein(s) produced. Most minor modifications to the genetic material
would be unlikely to cause changes to the protein that would be
significant from a human or nontarget organism perspective. Under Sec.
174.27(c)(2) EPA may consider such modifications on a case-by-case
basis. Many of the modifications are likely to produce proteins that
fall within the range of natural variation of the virus. However, it is
not currently possible to define clearly the range of variation of
viruses in general or even of any particular virus as discussed in Unit
IV.D. of the companion document published in today's Federal Register.
Therefore, Sec.  174.27(c)(2)(i) requires an Agency review to determine
qualification.
    PVCP-PIPs are known to confer resistance by two mechanisms.
Resistance may be either protein-mediated, in which the level of
resistance is correlated with the level of protein expression, or it
may be RNA-mediated, in which the level of resistance is not correlated
with the level of protein expression. (See discussion in Unit II.E.) In
the case of RNA-mediated resistance, little to no PVC-protein may be
produced from the PVCP-PIP. In such cases, little to no risk due to
protein production would be associated with the PVCP-PIP. However, the
Agency believes that the only conditions that can a priori indicate
there will be no protein production are encompassed by the criterion in
Sec.  174.27(c)(1). Any other type of construct that may confer RNA-
mediated resistance through PTGS would be reviewed by the Agency under
the criterion in Sec.  174.27(c)(2)(ii). A PVCP-PIP would meet Sec.
174.27(c) if EPA determines that no PVC-protein is produced from the
PVCP-PIP.
    If protein is produced, today's proposed exemption would cover only
those PVC-proteins that are not significantly different from naturally
occurring plant viral coat proteins, i.e., proteins that are virtually
unmodified or minimally modified. For more significantly modified PVC-
proteins, the base of experience upon which EPA relies for support of
the proposed exemption would not be applicable. Therefore, EPA would
not be able to make the determination a priori as part of this proposed
rule that the PVCP-PIP poses a low probability of risk to humans and
the environment and will not generally cause unreasonable adverse
effects on the environment even in the absence of regulatory oversight
under FIFRA. However, such PVCP-PIPs may still be eligible for
registration, and any significantly modified PVC-proteins could be
evaluated as part of the registration review (as discussed in Unit
II.G.). (For discussion of the concept of ``minimally modified'' see
Unit IV.E.2. of the companion proposed exemption published in today's
Federal Register.)
    3. Historical approaches. EPA's current proposed approach is
consistent with what EPA has always intended. EPA has never intended
that any proposed exemption for PVCP-PIPs would cover those PIPs that
produce proteins significantly different from those that occur
naturally (November 23, 1994, 59 FR at 60524; July 19, 2001, 66 FR
37865 and 66 FR 37796).

IV. Proposed Exemption for Certain Inert Ingredients

    As noted in Unit II.F. of this preamble, one of the general
qualifications for exemption at Sec.  174.21 is that ``any inert
ingredient that is part of the plant-incorporated protectant is on the
list codified at Sec. Sec.  174.485 through 174.490.'' EPA is proposing
to add several substances to Sec.  174.486 when they are used in a PIP
that is listed in 40 CFR part 174 subpart B - Exemptions and are in a
plant that satisfies Sec.  174.27(a):
     beta-D-glucuronidase (GUS) from Escherichia coli and the
genetic material necessary for its production,
     neomycin phosphotransferase II (NPTII) and the genetic
material necessary for its production,
     phosphomannose isomerase (PMI) and the genetic material
necessary for its production,
     CP4 enolpyruvylshikimate-3-phosphate (CP4 EPSPS) and the
genetic material necessary for its production,
     glyphosate oxidoreductase (GOX or GOXv247) and the genetic
material necessary for its production, and
     phosphinothricin acetyltransferase (PAT) and the genetic
material necessary for its production.
    Below is a summary of EPA's finding that these inert ingredients
present a low risk to human health and the environment; the docket for
this proposed rule contains the Agency's full risk assessment in the
document ``Environmental Risk Assessment of Plant-Incorporated
Protectant (PIP) Inert Ingredients.'' EPA also proposes to add to
subpart X the partial tetracycline resistance gene as present under the
control of a bacterial promoter in papaya line 55-1.
    EPA has conducted an environmental risk assessment of the PIP inert
ingredient phosphinothricin acetyltransferase (PAT) and the genetic
material necessary for its production. Topics covered in this
assessment include mode of action, ecological effects, endangered
species considerations, and gene flow from a modified plant to wild or
weedy relatives. Data cited in this assessment were submitted to the
Agency in support of Dekalb's DBT 418 and Ciba Seed's Event 176 Bt corn
registrations and Syngenta's COT 102 Bt cotton registration. Ecological
data and published information on the biology of this protein indicate
that this PIP inert ingredient is not known to be toxic and/or
pathogenic to plant or animal species. In 1997, the Agency granted a
tolerance exemption for this PIP inert ingredient in all plants due to
the low human health risks associated with this protein (40 CFR
180.1151; 62 FR 17717, April 11, 1997). Based on all of its
assessments, EPA has determined that this inert ingredient will pose
low ecological and occupational risk.
    EPA has conducted an environmental risk assessment of the PIP inert
ingredient CP4 enolpyruvylshikimate-3-phosphate synthase (CP4 EPSPS)
and the genetic material necessary for its production. Topics covered
in this assessment include mode of action, ecological effects,
endangered species considerations, and gene flow from a modified crop
to wild or weedy relatives. Data cited in this assessment were
submitted to the Agency in

support of Monsanto's MON 810 Bt Corn registration. Ecological data and