Genetics of downy mildew resistance in indigenous cucumber germplasm

Abstract

Cucumber (Cucumis sativus L.) is a major Cucurbitaceous vegetable crop widely grown in tropical and subtropical regions worldwide. Downy mildew is the most dangerous disease in cucumbers worldwide, causing significant yield loss. The vast diversity of economically important traits, including severity to downy mildew infestation, is available in Indian-originated germplasm. In order to investigate the genetic inheritance of cucumber downy mildew disease resistance, one resistant genotype (DC-70) from India was crossed with a contrasting susceptible genotype (DC-773). The parents and their progenies were evaluated in field and net house conditions for downy mildew disease resistance. Field condition data were recorded 4 times from 30 days until the plants died. The lower leaf surface was inoculated 20-25 days after sowing at the seedling stage by spraying the inoculum. The proportion of infection was recorded 4 times from 8 days to 65 days after inoculation, and the per cent disease index and area under the disease progress curve (AUDPC) were calculated from these proportions. Based on the PDI and AUDPC, it was established that a major gene controlled resistance to downy mildew in the genotype DC-70. Additive-dominance model fits the segregation data, and the additive effect was significant. Finally, the downy mildew disease inheritance pattern indicated that it is controlled by a single recessive gene in DC-70, which can be successfully introgressed into desired elite genotypes to facilitate the downy mildew resistance breeding programme.