Evaluation of Onion Germplasm for Resistance to Leaf Blight Caused by Stemphylium vesicarium

Leaf blight of onion caused by Stemphylium vesicarium is the most destructive fungal disease worldwide, which leads to decrease quality and seed production of onion. This study was conducted to evaluate the resistance degree of 110 onion germplasm against S. vesicarium. To investigate resistance to leaf blight, the genetic resources of onion were tested by following method. Onion seedlings at four-leaf stage were rubbed with nonabsorbent cotton and inoculated with spore suspension (1.0×105 spores/ml of potato dextrose broth) of S. vesicarium by spray method. Five to 7 days after inoculation, infected leaf area (%) of onion seedling was measured. Our results showed that IT274921, IT304144, IT274929, and IT274930 lines exhibited the highest resistance against S. vesicarium. And IT330615 and IT288913 lines was identified as moderately resistant to leaf blight, whereas IT299972, IT327434, IT337262, and IT337275 lines were the most susceptible cultivars to the fungus. On the basis of the results, we suggest that the resistant genetic resources can be used a basic material for resistant onion breeding system against leaf blight.