Genetic diversity among isolates of Phaeomoniella chlamydospora on grapevines

Phaeomoniella chlamydospora is one of the main causal agents of Petri disease and esca of grapevines. Although it is known to have a coelomycete synanamorph, no teleomorph has thus far been reported for P. chlamydospora, and its disease cycle remains largely unknown. The present study compared the genetic diversity of P. chlamydospora isolates from different grapevine-growing countries using amplified fragment length polymorphisms. Sixty-three isolates from South Africa and 25 from grapevine regions in Australia, France, Iran, Italy, New Zealand, Slovenia and the USA were studied. Two primer combinations were used producing 138 scorable markers, of which 33% were polymorphic. An unweighted paired group method of arithmetic averages analysis showed a high similarity (¿94.5%) among the different isolates. The overall low level of genetic variation confirmed asexual reproduction to be dominant in the field. Different genotypes were found among isolates of P. chlamydospora within the same grapevine, suggesting multiple infections from different inoculum sources. Isolates from different production areas and countries had a high percentage of similarity and clustered together, indicating the absence of genotype¿geographic structure. The presence of the same genotype in different vineyards and production areas suggests that long-range dispersal through aerial inoculum or infected plant material play an important role in genotype distribution