Multi-environment evaluation reveals diverse downy mildew pathotypes and region-specific breeding needs in cucumber

Downy mildew (DM), caused by Pseudoperonospora cubensis , is a major constraint in cucumber ( Cucumis sativus L.) production, particularly in humid and subtropical agro-ecologies. To identify stable sources of resistance and understand genotype-by-environment interactions, a comprehensive evaluation of 131 cucumber accessions was conducted across three contrasting agro-climatic locations in India: New Delhi (IARI), Bengaluru (IIHR), and Varanasi (IIVR). Field evaluations under natural epiphytotic conditions and artificial inoculations were performed, and disease incidence was assessed using the per cent disease index (PDI) and the area under the disease progress curve (AUDPC). Clustering analysis revealed significant genetic variability for DM resistance across environments. At IIHR, 29 genotypes, including IC523700, IC421752, and IC314341, exhibited high resistance (mean PDI ≤ 17.3; AUDPC < 700), while IIVR identified 35 highly resistant accessions with a mean PDI of 13.8 and AUDPC of 487.8. Several landraces, notably IC588146 and IC421752, demonstrated stable resistance across multiple locations, highlighting their potential as broad-spectrum resistance donors. At IARI, 11 genotypes were clustered together, including IC421752 and IC527400, which had the lowest PDI and AUDPC. The observed location-specific disease responses underline the prevalence of diverse DM pathotypes and the necessity for region-tailored breeding strategies. The study emphasizes the value of indigenous germplasm in developing climate-resilient, disease-resistant cultivars through multi-location screening and genomic approaches. Identified resistant accessions provide a valuable foundation for marker-assisted selection and breeding programs targeting durable DM resistance in cucumber.