Identification of novel resistant sources and inheritance of ToLCNDV resistance in cucumber (Cucumis sativus L.) germplasm

Abstract

Tomato leaf curl New Delhi virus (ToLCNDV) is a major constraint in cucumber (Cucumis sativus L.) cultivation, causing yield losses ranging from 17.6 to 99.4%. Although resistant sources have been identified in some cucurbits, no commercial ToLCNDV-resistant cucumber variety is presently available. Fifty indigenous cucumber genotypes were evaluated under natural epiphytotic conditions during kharif 2021 and 2022, followed by artificial screening of 17 promising genotypes in 2023–2024 using both whitefly and Agrobacterium-mediated inoculation. Quantitative PCR-based virus titre estimation was undertaken in six representative genotypes. A significant year × genotype × time interaction revealed variable disease progression patterns. Genotypes DC-70, DC-61, DC-91, DC-45 and WBC-17 consistently exhibited resistance (VI < 25), whereas DPaC-21, DC-769, DC-773, Sl-749 and Pusa Parthenocarpic Cucumber-6 were highly susceptible (VI > 75) across years. Cluster analysis, supported by principal component analysis and K-means clustering, grouped the genotypes into four distinct clusters. Three genotypes (DC-70, DC-60 and DC-91) maintained resistance across both natural and artificial screening conditions. qPCR results validated phenotypic reactions. Inheritance analysis from a cross between resistant (DC-70) and susceptible (DC-773) genotypes revealed the segregating ratio 3:1 in F2 and 1:1 in BC1 P1 populations, confirming the genetic control by a single recessive gene. The identified resistant genotypes constitute valuable genetic resources for breeding ToLCNDV-resistant cucumber cultivars.