an evaluation on the resistance of the germplasm of cucumber against downy mildew of cucurbitaceae (pseudoperonospora cubensis)

abstract downy mildew of cucurbits is one of the most important diseases of cucumber in humid areas and greenhouses. damage of disease is estimated 50% to 100% in suitable climatic conditions. therefore, achieving resistant or tolerant genotypes can be designed as the most important and safe method to reduce the damage and increase the benefits of cucumber farming. in order to evaluate the resistance of cucumber germplasms available in iran, an experiment was conducted using 72 genotypes including 20 native genotypes from iran national gene bank, 49 commercial hybrids from different seed companies, and 3 native population from tabriz (basmendj), babol (local babol) and cossackitan (local cossack). the mentioned genotypes were inoculated with 5 ml of 5×103 of sporangium. in field conditions, 21 genotypes, with local sari, were studied. it was resulted that voyaj f1 from russia and kc361065, kc361105 and tn 94135 from iran national gene bank, and gh5 as a commercial cultivar showed resistance under greenhouse conditions. fdc101 was considered resistant. it was concluded in vitro 4 genotypes and in vivo 8 genotypes found tolerant, whereas, were grouped in susceptible category. in this study, different reactions of fungus isolates were detected in some genotypes. this showed the existence of physiological races for pseudoperonospora cubensis in iran.