Intraspecific variation in Diplodia seriata isolates occurring on grapevines in Spain

Variation of Diplodia seriata, a fungal species associated with botryosphaeria dieback of grapevine, was investigated with respect to its genetic, phenotypic and pathogenic characteristics. The inter‐simple sequence repeat (ISSR) technique was used to investigate the genetic diversity of 83 isolates of D. seriata. Five ISSR primers were able to provide reproducible and polymorphic DNA fingerprint patterns, thus showing a relevant genetic variability in the species. Analyses of ISSR data by different clustering methods grouped the isolates into two distinct clusters through the Bayesian and DAPC analyses. No relationships between either geographic or host origin of isolates and genetic clusters were observed. Several representative isolates from each genetic cluster were chosen for studying their conidial dimensions, in vitro mycelial growth, vegetative and mating compatibility, and pathogenicity on detached grapevine canes and potted vines. No significant differences in conidial dimensions were detected among the groups. Vegetative compatibility reactions were observed among isolates but this was not related with the genetic clustering. Production of sexual fruiting bodies in vegetative compatible crossings was not observed under the experimental conditions used in the study. All 14 isolates tested for pathogenicity were confirmed to be pathogenic according to the length of the necrotic lesions that they caused and their reisolation frequencies from the infected plant tissues. Differences in the length of necrosis were detected among isolates, thus revealing the existence of different virulence levels in the species.