Phenotypic categorization of resistance against infection by two Begomovirus (slccnv and tolcndv) species in Cucurbita moschata duchesne

Squash leaf curl China virus and tomato leaf curl New Delhi virus are the two most prevalent begomovirus species in India, causing 100 per cent crop losses in pumpkin. The present study was envisaged to develop a disease rating scale for SLCCNV, ToLCNDV, and their mixed infection in Cucurbita moschata. The disease severity of both viruses was assessed at different stages viz., nursery, 45 days after sowing (DAS)and 75 DAS to identify the best stage and scale for selecting resistant genotypes to be used in breeding programmes. Based on disease reaction, 10 genotypes were classified into four phenotypic classes viz., resistant (1), moderately resistant (2), moderately susceptible (1) and susceptible (6) against these viruses. PVR-1343 showed resistant disease reaction, whereas P-1327 and P-6777 were moderately resistant. Disease expression of all the genotypes changed from nursery stage to 45 DAS along with quantum jump in their coefficient of infection values. However, the same disease reaction was exhibited by all the genotypes from 45 to 75 DAS. Thus, the disease rating scale at 45 DAS is appropriate and effective in terms of resources and time for identifying resistant genotypes in pumpkin. The genotypes expressed similar resistance level with PVR-1343 depicting resistance against both viruses alone and in mixed infection. It can be further utilized in hybridization programmes to develop resistant hybrids and/or to transfer disease resistance into well adapted C. moschata varieties.