Screening of ridge gourd genotypes for resistance to downy mildew (Pseudoperonospora cubensis)

Downy mildew caused by Pseudoperonospora cubensis is one of the major production constraints of ridge gourd cultivation causing severe yield loss. Host resistance is the most effective and sustainable means of controlling this disease. Ten varieties and thirteen advanced breeding lines of ridge gourd were screened under natural epiphytotics for two seasons and ten moderately resistant lines were identified based on per cent disease index (PDI). Among them, two lines IIHR-DMR-18-4-4 and IIHR-DMR-18-65-1 clearly showed lower disease severity with PDI of 23.46 and 24.03, respectively, while highly susceptible lines showed higher disease severity with 73 PDI. The area under disease progress curve (AUDPC) values of the moderately resistant lines IIHR-DMR-18-4-4 and IIHR-DMR-18-65-1 (1171.86 and 1190.86) were one third of those of the highly susceptible lines (3648.35). Similarly apparent infection rate (r) per week was lower in the moderately resistant lines (0.88) than in the susceptible lines (1.23), indicating slow disease progression (slow mildew) in these moderately resistant lines. Moderate resistance reaction was confirmed by the production of fewer sporangia/cm(2) (1.08 x 10(4)/cm(2)) and lower percentage of infected leaf area (8.6%, 8.4%) which was almost ten times less than that observed in highly susceptible lines such as Pusa Nasdar and Jaipur Long with high sporangia production (1.48 x 10(5)/cm(2),1.14 x 10(5)/cm(2)) and leaf area damage (67.8%, 76.9%) respectively. The identified moderately resistant lines IIHR-DMR-18-4-4 and IIHR-DMR-18-65-1 showed slow mildew development and can be utilized in the breeding program to develop resistant cultivars of ridge gourd with desirable horticultural traits.