Studies on Pseudopernospora cubensis Causing Downy Mildew of Cucumber and in-vivo Assay for Management

Abstract:

Downy mildew, caused by the obligate oomycete Pseudoperonospora cubensis, is a highly destructive foliar disease limiting cucumber productivity globally and regionally. To assess the contemporary distribution and spatial severity of this disease in Southern Rajasthan, an extensive roving survey was conducted across 44 farmer fields in 17 tehsils across Udaipur, Chittorgarh, and Banswara districts during the Kharif season of 2024–25. Disease severity was quantified using the Percent Disease Index (PDI) based on a standard 0–5 rating scale. Symptomatological monitoring revealed typical angular, vein-limited chlorotic lesions on the adaxial leaf surfaces, corresponding to a dense grey-brown to black downy sporulation on the abaxial surfaces under high humidity. The survey revealed widespread prevalence with significant geographic variation in disease intensity. The highest structural district-mean PDI was recorded in Banswara (30.86%), followed by Udaipur (26.22%), while the lowest disease pressure was logged in Chittorgarh (25.20%). At the sub-district level, the highest disease severity was documented in Bagidora tehsil of Banswara (48.21% PDI within specific fields; tehsil mean 32.11%) and Kotra tehsil of Udaipur (mean 36.50% PDI). Conversely, the minimum localized infestation was recorded in Jhadol tehsil of Udaipur (12.32% PDI within a single site). The heightened disease clusters in Banswara and specific humid tracts of Udaipur correlate directly with dense microclimates, high relative humidity, and traditional monocropping setups. This study maps the regional hot-spots of P. cubensis in Rajasthan, providing crucial epidemiological baselines for designing localized Integrated Disease Management (IDM) models.