 Three closely related "Mycosphaerella" species, "M. fijiensis", "M. musicola" and "M. eumusae" cause a destructive disease of bananas.Each of these three species is heterothallic, that is, matings can only occur between individuals of different mating type.Although the mating type DNA sequences of the three species appear to have arisen from a common ancestral sequence, there also has been considerable evolutionary divergence between them.