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Isabgol (Plantago ovata Forssk.) is a vital medicinal plant, highly valued for its substantial soluble fibre content and numerous health benefits. However, its cultivation is severely impacted by Alternaria leaf blight incited by Alternaria alternata, which affects both yield and quality. The present study was carried out during two winter (rabi) seasons of 2022–23 and 2023–24 at College of Agriculture, Swami Keshwanand Rajasthan Agricultural University Bikaner, Rajasthan to investigate the effect of various weather parameters on the progression of Alternaria leaf blight of isabgol. Results indicated that the highest percent disease intensity (54.38%) occurred during 29 January–04 February meteorological week in 2022–23, while in 2023–24, the peak disease intensity (51.11%) was observed during the 05–11 February week. Correlation analysis revealed that maximum and minimum temperatures, rainfall, and sunshine hours were significantly negatively correlated with disease intensity, whereas maximum and minimum relative humidity and wind velocity showed a positive correlation with disease intensity for the 2022–23 season. These findings highlight the critical role of weather attributes in the infection process and spread of Alternaria leaf blight in isabgol, providing essential insights for effective disease management strategies.

Isabgol (Plantago ovata) is a crucial medicinal plant valued for its high soluble fiber content, benefiting digestive health and cholesterol management. However, Alternaria leaf blight, caused by Alternaria alternata, poses a significant threat to Isabgol cultivation, impacting both yield and quality and necessitating effective disease management strategies. The experiment was conducted at the Department of Plant Pathology, College of Agriculture, Bikaner, Swami Keshwanand Rajasthan Agricultural University, Bikaner, Rajasthan, in dual culture techinique under controlled conditions to screen rhizosphere microorganisms for their antagonism against Alternaria alternata in Isabgol. The result showed that the significant variation in the reduction mycelial growth of pathogen in the presence of various microorganisms. Among all the tested antagonists, Trichoderma viride was the most effective, with maximum 83.9% mycelial growth inhibition of pathogen followed by Colletotrichum lindemuthianum (79.73%), Trichoderma harzianum (76.01%), Aspergillus flavus (73.98%), Rhizoctonia solani (72.16%), Fusarium spp. (71.30%), Trichoderma spp. (67.55%), Aspergillus parasiticus (67.23%) and Colletotrichum gloeosporioides (66.95%). These findings indicated that certain rhizosphere microorganisms possess substantial potential as bio control agents against A. alternata, and an environmentally friendly alternative to chemical control.

The Alternaria leaf blight disease of Isabgol is the new emerging plant disease, causing significant damage to crops. Recognizing its impact, a survey was conducted in the major growing areas of Isabgol in Rajasthan during rabi season 2022-23 and 2023-24. The survey conducted in various districts of Rajasthan revealed an average disease intensity of 24.03%, with Bikaner reporting the highest intensity (22.82%) followed by Jaisalmer (19.30%), and the lowest recorded in Barmer (11.67%). Further examination in Bikaner district during the Rabi seasons of 2022-23 and 2023-24 indicated fluctuating disease intensity ranging from 23.86% to 21.77%. Maximum disease intensity (29.07%) occurred in Isabgol fields in Ridi village, Shri Dungargarh tehsil, Bikaner, while minimum intensity (17.63%) was observed in Barsingsar village, Bikaner. In Jaisalmer, disease intensity ranged from 20.28% to 18.32%, with Moolana village reporting the highest (23.20%) and Keeta village the lowest (14.96%). Barmer exhibited an average disease intensity of 12.46% to 10.87%, with Gadario ki Dhani village (14.67%) in Gudha Malani tehsil showing the highest intensity at Nosar village (8.68%) in Baytoo tehsil the intensity was recorded lowest.