Researches on infection process of downy mildew disease and accumulation of important stilbenes in some grapevine genotypes

In this study, the resistance of 6 different grapevine genotypes [local wine grape Karasakız, local table grape Müşküle, cross table grape Tekirdağ Sultani (ItaliaXSuperior Seedless), brined crosses 119, 154 and 200 (NarinceXRegent)] to mildew disease caused by Plasmopara viticola was investigated in detail. During the experiments, inoculation was performed by dropping the sporangium suspension of the pathogen to the abaxial surface of detached leaves. The sporulation area (mm2) on leaves at a week after inoculation was first measured under a stereomicroscope, 200 was found as extremely resistant (ER), Müşküle and 154 as highly resistant (HR), 119 as resistant (R), Karasakız as sensitive (S) and Tekirdağ Sultani as highly sensitive (HS). A significant positive correlation was determined between the number of sporangium on the lesion and sporulation area. In the observation with a fluorescent microscope, the lowest number of infected stomata by pathogen at 48 hours after inoculation was determined in the genotype 200, Müşküle and 154 followed it. The vesicle of the pathogen germinated and developed primary hypha in the leaves of all genotypes at 24 hours after inoculation, however, in genotype 200, the primary hypha of vesicle did not spread into the intercellular spaces of the mesophyll at 48 hours after inoculation. Although this spread occurred at this process in Müşküle, 119 and 154, the development of the pathogen was restricted at 72 hours after inoculation. Pathogen with long branched hypha having many haustoria developed mycelia and covered the intercostal field in sensitive genotypes at 72 hours after inoculation. The amount of three3 stilbene compound (resveratrol, ε-viniferin and pterostilbene), which was measured in high pressure liquid chromatography (HPLC), significantly increased in resistant genotypes at increasing time periods after inoculation. The amount of resveratrol was found to be high in 72 hours after inoculation in genotypes which are resistant to pathogen at different level, while the highest amount of ε-viniferin was determined in genotype 200 (ER) during this period. Müşküle (HR) and 154 (HR) contained higher amounts of pterostilbene than that of other resistant genotypes. This study shows that the defense mechanism that limits the progression of the disease during the infection of the pathogen was induced in Müşküle, 119, 154 and 200 whose resistance against P. viticola was tested for the first time.