QTL-seq reveals Cy-2 as a major locus on chromosome 7 and associated candidate genes conferring resistance to ToLCNDV in cucumber

• Tomato leaf curl New Delhi virus resistance deciphered in Cucumis sativus using integrated QTL-seq and transcript profiling. • Discovery of a novel major-effect QTL (Cy-2) on chromosome 7 (~1.8 Mb) governing ToLCNDV resistance. • High-resolution Δ(SNP-index)-based mapping enabled rapid identification of resistance-associated genomic intervals. • Development of diagnostic markers (SSR00931, AMS12-InDel, AMS13-CAPS) tightly linked to the resistance locus. • Candidate defense genes (LRR-RLKs, PR proteins, secondary metabolism enzymes) prioritized through expression validation. • Provides a first robust genomic framework for ToLCNDV resistance breeding in cucumber. • Molecular insights into begomovirus-host interaction and antiviral defense architecture in cucurbits.