EVIDENCE OF MATING IN NATURE BETWEEN INDIVIDUALS OF ERYSIPHE NECATOR FROM DIFFERENT GENETIC GROUPS

Erysiphe necator (formerly Uncinula necator) is a biotrophic ascomycete that causes powdery mildew on grapevine. For this pathogen, two sympatric populations (groups A and B) have been described in Europe and Australia. The two genetic groups differ in multiple genetic loci and previous studies reported a lack of interfertility. Twenty flagshoots were sampled in an untreated vineyard in Emilia-Romagna (northern Italy) early in the growing season, and one single-conidial isolate was obtained from each. Additional single-conidial isolates were obtained from infected leaves and berries later in the epidemics. Cleistothecia were collected in the same vineyard from leaves before senescence, and from bark, before budbreak in the following season. DNA was purified from 60 single-conidial isolates and from 250 cleistothecia and used as template for PCR to amplify -tubulin and IGS sequences. Amplified DNA from these two loci was digested with AciI and XhoI, respectively, to show single-nucleotide polymorphisms specific for the two genetic groups. Individuals of genetic groups A and B coexisted in the vineyard throughout the season, with no change in frequency. DNA amplified from cleistothecia showed the presence of markers diagnostic for both groups A and B and a mixture of the two. Mixtures of A and B were found in 12% of cleistothecia collected in autumn and in 36% of cleistothecia collected in spring from the bark. These results indicate that these two groups mated and produced ascospores in nature, although we found no evidence of recombination between A and B in field isolates.