Epidemiology, screening of isabgol (Plantago ovata Forsk.) genetic material for resistance sources to downy mildew disease and management strategies

Downy mildew caused by Peronospora plantaginis is one of the major threats to isabgol production, resulting in substantial yield losses of crop. The disease incidence varied from 50 to 100% and disease severity index (DSI) level ranged from 40 to 75% on isabgol. Despite of its economic impact, there has been a paucity of information available on epidemiology and resistance sources of isabgol. The research has unveiled critical role of weather factors in development of downy mildew, where, dew precipitation being a pivotal factor for sporangiospores germination showed positive correlation with disease severity. The prevailed minimum temperature 10 °C to maximum temperature 25–30 °C when coincided with night dew precipitation, high relative humidity (> 85%) and less bright sunshine hours (6 to 8 h), favored downy mildew severity. In the present study, 213 breeding lines, 160 recombinant inbred lines (RILs), 75 germplasm of isabgol and 6 Plantago species were screened for resistance against downy mildew disease. The lowest disease severity among the breeding lines was 0.47 ± 0.09 on DPO-185 and the highest 8.10 ± 0.06 recorded on DPO-183; in RILs the lowest was 0.66 ± 0.05 on RIL-4 and the highest was 7.99 ± 0.09 on RIL-32, and in germplasm lowest DSI 0.8 ± 0.24 recorded on PB-80. Additionally, the efficacy of nine fungicides was evaluated by applying three consecutive spray and the mixed ψ Metalaxyl 4% + Mancozeb 64% was found to the best in suppressing the disease severity (84.9%) over the check. The identified resistant lines hold promise for the development of resistance varieties. The findings of epidemiological investigation and fungicides evaluation will offer the valuable insights for devising management strategies to mitigate the losses caused by downy mildew disease in isabgol.