Identification of sources of resistance to an Indian isolate causing Gummy stem blight in watermelon

Gummy stem blight caused by the fungus Stagonosporopsis cucurbitacearum (syn. Didymella bryoniae ), is a devastating disease of watermelon all over the world including India. Several strategies are being explored for the management of this disease. Though cultural and chemical management gives partial relief, the development of resistant cultivar is cost-effective and environment friendly. However, the development of resistant varieties for this disease is constrained by the non-availability of suitable resistant sources. Hence, in the present study, we evaluated a panel of watermelon germplasm for the identification of resistance sources against gummy stem blight. A total of 266 genotypes of watermelon comprising of 260 germplasm collections and six commercial checks were evaluated for the identification of resistance sources under artificial screening and natural epiphytotic conditions. A highly virulent watermelon isolate (MN396362) obtained from the research farm of Division of Vegetable Crops, ICAR-IIHR was used for artificial screening, employing mycelial disc inoculation technique. Host response in terms of symptom expression ranging from necrosis in leaves, stem cankers, rotting of the infected stem to complete wilting and death of plants were observed. Among the genotypes evaluated, IIHR-617, IIHR-82, IIHR-545, BIL-53 and IIHR-556 were found to be resistant. These potential sources of resistance identified shall be of great value in developing gummy stem blight resistant varieties of watermelon.