Genetics of downy mildew resistance in indigenous cucumber germplasm

Abstract

Cucumber (Cucumis sativus L.) is a major Cucurbitaceous vegetable crop widely grown in tropical andsubtropical regions of the world. Downy mildew is the most damaging disease in cucumber worldwide causingsignificant yield loss. The wide diversity in terms of different economically important traits including severityto downy mildew infestation is available in Indian-originated germplasm. To investigate the genetic inheritanceof cucumber downy mildew disease resistance, one resistant genotype (DC-70) from India was crossed with acontrasting susceptible genotype (DC-773). The parents and their progenies were evaluated in both field andnet house conditions for downy mildew disease resistance. Field condition data were recorded 4-times from30 days until the plants die. The lower leaf surface was inoculated 20-25 days after sowing at the seedlingstage by spraying the inoculum. The proportion of infection was recorded 4-times from 8-days to 65-daysafter inoculation, and the per cent disease index and area under the disease progress curve (AUDPC) werecalculated from these proportions. Based on the PDI and AUDPC, it was established that resistance to downymildew in the genotype, DC-70 was controlled by a major gene. Additive-dominance model fits the segregationdata and the additive effect was significant. Finally, the downy mildew disease inheritance pattern indicatedthat it is controlled by a single recessive gene in DC-70, which can be successfully introgressed into desiredelite genotypes to facilitate the downy mildew resistance breeding programme.