Studies on pathogenicity differences of the fungus isolates of Ascochyta fabae Speg., the causal agent of Ascochyta blight and evaluating the resistance of the faba bean cultivars to disease

Ascochyta blight caused by the fungus Ascochyta fabae Speg., is known as one of the most destructive diseases of faba bean worldwide. Yield losses due to attacks by this fungus can reach more than 90% when cultivars are sown under cool and wet conditions. Disease Control by using crop rotation, clean seed and chemical treatments cannot be fully effective. Therefore, using the resistant cultivars as a reduction factor of the disease severity and infection type is very important for disease control. At first, different fungal isolates were collected from northern areas of Iran, purification and pathogenicity was carried out on the susceptible cultivar of Barkat with spore suspension by concentrations of 106 spores per ml on leaves in the greenhouse condition. For identifying isolates virulence, the fungus inoculated was done on the susceptible cultivar of Barkat like pathogenicity test method. Disease severity index implemented when the symptoms appeared and was carried out 15 days after sporulating by Sillero and Rubiales method. The responses of 14 faba bean genotypes and cultivars were evaluated to disease in randomized complete block design in field conditions with three replications. Among total sampling of different regions, 10 pure isolates of A. fabae with high virulence totally obtained which indicated a high variability in Mazandaran and Golestan provinces. The results of resistance evaluation of faba bean genotypes and cultivars in field conditions revealed the resistance response of genotypes of G-faba-67, G-faba-95, G-faba-100, G-faba-133 and Zereshki cultivar along with disease severity index 25.66 to 40.33 percent and the other cultivars (6 genotypes and 3 cultivars) equal to 64% of all tested cultivars susceptible and genotypes showed a susceptible or highly susceptible response.