Evaluation of Hazelnut (Corylus avellana L.) Cultivars on Susceptibility to Brown Leaf Spot Fungus, Mamianiella coryli

Brown leaf spot (leaf blight) is a fungal disease caused by Mamianiella coryli, causal agent of early defoliation in summer, and is widely distributed in hazelnut (Corylus avellana L.) growing regions of Iran. During 2019-2020, 48 native and foreign hazelnut cultivars/ and or genotypes were evaluated for susceptibility against M. coryli under natural infection conditions at Astara Horticultural Research Station (northern Iran). One hundred infected leaves were randomly collected from four geographical directions and middle of canopy of each hazelnut tree. Disease severity index (DSI%) on leaves was calculated based on 1-5 rating system (1= >0 to 20% leaf area affected and 5= >80% of leaf area affected) and levels of reactions were determined based on DSI% (<1%= Highly resistant and >50%= Highly susceptible). None of the hazelnut cultivars had genetic resistance to M. coryli and all of the genotypes were grouped into two categories included susceptible (25.1-50%) and highly susceptible. Seven cultivars and/or genotypes included Souchi, Gerdoii 89, Pashmineh 89, Rimsky, Segorbe, Dedobestani and Pronnes were high susceptible and the rest were in the susceptible categories. It was concluded that sanitation of leaf debris in the fall, pruning for better air circulation or fungicide applications in the spring might be useful in disease outbreak conditions.