susceptibility evaluation of different cultivars of hazelnut (corylus avellana l.) to powdery mildew (phyllactinia guttata) in northern iran

Hazelnut (corylus avellana l.) production is well-established in iran. cultivars that are resistant to plant diseases are needed to expand hazelnut cultivation. the present research aimed to study and compare the susceptibility of 48 iranian, local and exotic hazelnut cultivars (c. avellana l.) to phyllactinia guttata, the pathogen causing powdery mildew (pm). the study was conducted under naturally occurring infection at a research station for hazelnut in the guilan province (astara-north of iran), during the period 2019-2020. experiments were arranged in a randomized complete block design with four replicates. the studied cultivars were divided in classes of susceptibility to ph. guttata depending on the leaf infection (%) and disease severity index (dsi), using a 8-rating scale (0= no visible leaf symptoms to 7 = more than 85% of the leaf surface with symptoms). none of the investigated cultivars demonstrated resistance. although no plot was scored less than 4, highly significant differences (p=0.01) in susceptibility among hazelnut cultivars were found. so that, 75% of the hazelnut cultivars exhibited high susceptibility to pm. no correspondence was observed within cultivars based on geographical origin. in general, iranian superior local cultivars gercheh, pashmineh 89, shast-e-ras, gerdoii 89 and four spanish commercial cultivars fertile de coutard, segorbe, negret, and 'ronde du piedmont showed high susceptibility reaction to pm. it was recommended that while paying attention to the susceptibility of cultivars to pm, control measures should also be considered.