Botrytis four species are associated with chocolate spot disease of faba bean in Latvia

Faba bean (Vicia faba L.) is gaining importance as a crop in northern Europe. In this region, the most important disease of faba bean is chocolate spot disease, attributed to the pathogen Botrytis fabae. However, other Botrytis species have been found to contribute to the disease. Hence, it was decided to isolate fungi from faba bean plants showing symptoms of chocolate spot disease in Latvia, identify the Botrytis species using the DNA sequences of three definitive genes, evaluate the morphological diversity of the isolates in vitro and, finally, to determine the pathogenicity of the isolates in a detached-leaf test. In addition to B. fabae, B. cinerea, B. pseudocinerea and B. fabiopsis were all identified. Phylogenetic analysis of the DNA sequences put all the obtained 44 isolates unequivocally into clusters with known examples of each species. Every species showed wide diversity in its in vitro colour, texture and growing pattern of mycelium, production of sclerotia and pigmentation of the growing medium with much overlap between species showing that this method is not adequate for species discrimination. B. fabae produced the largest lesions on infected leaves, followed closely by B. pseudocinerea and B. cinerea, while B. fabiopsis produced much smaller lesions. The results show that chocolate spot disease of faba bean is attributable to Botrytis four species in northern Europe. This knowledge needs to be considered when controlling the disease by genetic or agronomic means.