Evaluation of relative resistance of different hull-less seed oil pumpkins to powdery mildew

Powdery mildew is one of the most important diseases of cucurbits in the world and Iran. The disease is found in cucumbers, melons, cantaloupes, squash, and watermelons in both farm and greenhouse conditions and causes great damage. Cultivating resistant cultivars or chemical control with fungicides can be used to control this disease. In this study, 28 different genotypes of hullless seed pumpkin were studied and compared for powdery mildew resistance in potted conditions in a greenhouse. To achieve this, the genotypes in the greenhouse were sprayed with powdery mildew spores, and when signs of powdery mildew appeared through infection on the plants, the severity of the disease was determined by image processing using a program written in MATLAB software. The mean comparison showed that the lowest level of infection was related to lines 11 and 23 and hybrids of 7×16, 2×16, and 2×23. The highest negative general combining ability was related to line 11 and the highest negative specific combining ability was related to hybrids 7×14, 2×16, 2×23, and 11×14. The highest negative heterosis compared to the high parent was related to 11×14, 2×23, and 2×16 hybrids. Due to the significant values obtained for specific combining ability and significant heterosis in hybrids, the role of dominance variance in controlling this trait is prominent, and hybrid production is recommended to improve resistance to powdery mildew.