Evaluation of commercial varieties and hybrids for resistance to gummy stem blight in watermelon

Abstract

Gummy stem blight (GSB), caused by Stagonosporopsis cucurbitacearum, is a major constraint in watermelon production, necessitating the identification of resistant cultivars for effective disease management. In the present study, twenty commercial watermelon varieties and hybrids sourced from public and private seed agencies were screened under controlled polyhouse conditions using artificial inoculation techniques. Multiple inoculation methods—leaf spray, root inoculation, leaf disk placement, and stem injection—were evaluated for their reliability in symptom expression. Among these, the stem injection method consistently produced uniform, systemic, and scorable symptoms and was therefore selected for detailed screening. Ten-to fifteen-day-old seedlings were inoculated with the SC-W10 isolate, and disease severity was assessed using 0-9 disease scale with Percent Disease Index (PDI) calculated using McKinney’s formula. Disease progression was strongly influenced by humidity, with >90% relative humidity promoting rapid symptom development. Based on PDI values, nine hybrids—IB-20, Melody, Arka Shyam, Arka Aishwarya, AFA-205, AFA-306, AFA-505, SS-345, and SS-906—exhibited lower disease severity and were categorized as moderately susceptible. Five hybrids (NS-295, Ayush, Arka Manik, Arka Muttu, and Black Beauty). The findings highlight significant variability in host response and identify promising genotypes for use in resistance breeding and integrated management of gummy stem blight in watermelon.