Screening of onion genotypes and varieties against onion twister disease caused by Colletotrichum and Fusarium

Abstract

Twister disease of onion, caused by a complex of Colletotrichum and Fusarium, poses a serious threat to onion production. The present study was undertaken to evaluate onion genotypes for resistance to twister disease under glasshouse conditions and to elucidate biochemical changes during disease development. Thirty-one onion entries were evaluated through combined artificial inoculation with Colletotrichum and Fusarium. Results indicated that none of the genotypes exhibited immune or resistant reactions. Two varieties, Bhima Dark Red and Bhima Shubhra, were identified as moderately resistant. Six entries were categorized as moderately susceptible, twelve as susceptible and eleven as highly susceptible. Among the genotypes, white onions were found to be more susceptible (65.17 PDI) than red onions (50.85 PDI). Among the varieties, the disease intensity ranged from 19.44 to 50.00 PDI, with a mean of 37.61 PDI, indicating a moderately susceptible reaction. The susceptibility of white onion suggests the role of active biochemical compounds, including sulfur compounds, flavonoids, phenolic compounds and anthocyanins. In addition, physical barriers like the thinner epidermal cell layers and higher moisture content in white onion tissues create a more favourable environment for spore germination and appressorial penetration. While no genotype showed complete resistance to twister disease, the moderately resistant entries represent valuable genetic resources for strengthening resistance through future breeding efforts.