Determination and identification of Podosphaera xanthii (=Sphaerotheca fuliginea Pollachi) and Golovinomyces cichoracearum (=Erysiphe cichoracearum D.C) causal agents of powdery mildews on domestic, wild and commercial cucurbits and searching resistant cucurbit genotypes against these pathogens

Cucurbits are very important vegetable group significantly produced in Turkey and in the world. There are diseases that limit the production of these vegetables. Powdery mildew diseases are leading to cause economic losses in the production. The obligate fungal pathogens, Podosphaera xanthii and Golovinomyces cichoracearum are destructive for cucurbits. There is no resistant cucurbit variety against to powdery mildew disease known yet. The aim of this study is to identify genetically resistant plants from landraces, wild and commercial cucurbits such as pumpkin, melon, watermelon, cucumber collected between west and east Mediterranean regions. Powdery mildew inoculated and maintained on a susceptible cucumber variety (baccara). Inoculations were conducted by using the powdery mildew conidiophores and spores with spreading on to the cucurbit leaves in air-tight place. The single spore produced powdery mildew was identified as Podosphaera xanthii according to morphological and microscopic studies. Furthermore, the powdery mildew pathogen was verified to be Podosphaera xanthii by 99% of the pathogen as results of conducted molecular analysis. A total of 34 local, wild and commercial cucurbit species inoculated with P. xanthi. The inoculated cucurbit plants were examined by trypan blue, diamino benzidine and 3,3'-dihexyloxacarbocynin iodide (DiOC6) staining methods during the first 3 days post inoculation. On the next 7th, 14th and 21st days post inoculation, disease development on the inoculated plants was scored according disease scale and resistant and susceptible cucurbits genotypes were found. The pathogenicity test results revealed that VT18, Meltem F1, Poyraz F1 and 348 commercial cucumber varieties and Adana courgette, Kaledran cucumber 1 and Kaledran cucumber 2 landraces were the most resistant cucurbit genotypes. However, these pathogenicity tests have also resulted Kaledran melon 2 was the most susceptible landrace genotype against the P. xanthii. In future studies, these resistant local, wild, and commercial genotypes will be able to use against destructive powdery mildew pathogen, P. xanthii as sources of resistance. Currently, there are no genetically resistant plant varieties in cucurbits allowing applications of chemical pesticides for controlling the powdery mildews.