Identification of novel ToLCNDV-resistant Luffa accessions through integrated field and artificial screening approaches for genetic enhancement

Tomato leaf curl New Delhi virus ( ToLCNDV ), a bipartite begomovirus, has increasingly become a major constraint to cucurbit production, posing serious challenges to the cultivation and genetic improvement of Luffa species. To date, only a limited number of resistant sources have been identified in Luffa , with the widely recognized accessions DSG-6 and DSG-7 representing the few exceptions. The present study aimed to identify sources of resistance to ToLCNDV among 200 Luffa accessions conserved in the National Genebank at ICAR-National Bureau of Plant Genetic Resources (NBPGR), New Delhi, representing collections from 22 states across India. Preliminary field screening conducted across four consecutive seasons ( spring–summer 2020 and Kharif seasons of 2020, 2021, and 2022). Eight genotypes exhibited a resistant reaction with a Vulnerability Index (VI) of ≤ 20.Vulnerability Index (VI)-based disease response remained consistent across Kharif evaluations conducted from 2020 to 2022. However, within 2020, VI-based disease severity was significantly higher during Kharif season than during spring–summer season, likely due to increased whitefly pressure. These genotypes were subsequently challenged with ToLCNDV through whitefly-mediated inoculation under controlled conditions. The genotypes IC343156, IC538150, IC398583, IC438825, IC394720, IC311134, IC383931 and IC393305 remained symptomless following inoculation. The presence of viral DNA was confirmed by polymerase chain reaction (PCR), confirming ToLCNDV infection, while the resistant response was determined based on the observed disease symptoms and severity. These resistant genotypes represent valuable genetic resources and serve as priority donor lines for breeding programs aimed at developing durable ToLCNDV -resistant Luffa cultivars.