STUDY OF GERMINATION AND PENETRATION OF POWDERY MILDEW FUNGUS ON SUSCEPTIBLE AND RESISTANT GRAPEVINE GENOTYPES AND INVESTIGATION ON THE RELATED ONTOGENIC RESISTANCE.

Powdery mildew caused by an obligate biotrophic fungus Erysiphe necator (synonym Uncinula necator) is the most economically important disease of grapevines. Most widely grown grape cultivars are highly susceptible to E. necator, because they are derived from Vitis vinifera, a species which was not exposed to this pathogen during its evolution. In this study we investigated germinating of grapevine powdery mildew on two susceptible and resistant grapevine genotypes as well as ontogenic resistance in vegetative tissues of Cabernet sauvignon and Arabidopsis thaliana with different age. Conidia germinated and appressorium and haustorium appeared during 2-12 hpi in both genotypes. The primary hypha developed 12 hpi in both genotypes however; yellow deposits could be seen surround epidermal cells 12 hpi just in resistant genotype. Development of primary hypha continued up to 24 hpi in susceptible Cabernet sauvignon, however, 24 hpi the hypersensitive reaction (HR) happened in resistant genotype and blocked secondary hypha development, but not in Cabernet sauvignon. By increased in physiological age related to ontogenic resistance the penetration efficiency of fungi in Cabernet sauvignon and Arabidopsis thaliana reduced. [ABSTRACT FROM AUTHOR]