The occurrence of cleistothecia ofErysiphe necator(Grapevine powdery mildew) and their epidemiological significance in some vine-growing regions of Hungary

Abstract

The main objectives of this study were to determine which of the two overwintering forms of Erysiphe necator (either by hyphae in grapevine buds or via cleistothecia on leaf, cane or trunk surfaces) dominate in different vine-growing regions of Hungary, and to find out their impact on initiating disease epidemics. The only evidence of mycelial overwintering of this fungal pathogen in grapevine buds in 2004 was found in a vineyard in Sióagárd where one single plant showed the typical symptoms of “flag shoot”, whereas in all other cases initial infections by ascospores from overwintering cleistothecia were evident. The appearance and spread of E. necator was quite similar in the vineyards of Eger, Kecskemét and Sióagárd, the first leaf symptoms appearing about three weeks before flowering, and by the time grape bunches became susceptible to powdery mildew attack, a significant amount of inoculum was available that resulted in up to 90–100% infection. Microscopical investigations revealed a relatively low percentage of parasitism of cleistothecia by Ampelomyces sp. in the grapevine cultivars examined.