Screening of rhizosphere microorganisms for antagonism against Alternaria alternata (Fr.) Keissler causing Alternaria leaf blight of Isabgol (Plantago ovata)

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.