GAUTAM, HARENDER RAJPARWAN, SONALI2021-09-242021-09-242021-09https://krishikosh.egranth.ac.in/handle/1/5810176191ABSTRACT The present study on Alternaria leaf spot of cauliflower (Alternaria brassicicola (Schwein.) Wiltshire) were undertaken in relation to prevalence during 2019 and 2020 crop seasons. Characteristic symptoms of the disease were characterized by the presence of yellow, dark brown to black circular leaf spots with target like concentric rings. Under warm and humid weather conditions, centers of the lesions may fall out, giving the leaf spots a shot-hole appearance. Individual spots coalesce into large necrotic areas and leaf drop can occur. The pure culture of the pathogen was isolated over PDA. While studying the morphology of the test pathogen it was found that the mycelia (2.5-6.02 μm) were brown or olivaceous brown, septate and profusely branched in old cultures whereas pathogen produced conidiophores of 35- 45×5-8 m on which dark conidia were formed which ranged from 44-55×11-16 m in size and had 5-8 transverse and 0-5 longitudinal septa and are muriform with no beak formation. On the basis of morphological characters, the associated pathogen was identified as Alternaria brassicicola (Schwein.) Wiltshire. Pathogenicity of Alternaria brassicicola was proved following Koch’s postulates on cauliflower cv. “Pusa Snowball K1”. The pathogen exhibited initial symptoms after 120.30 h and 62.10 h of inoculation on potted plants and detached leaves, respectively. For disease management, botanicals, yeasts and their combinations were evaluated against test pathogen both under in vitro and in vivo conditions. Among botanicals, Karvaya (Roylea elegans) (52.64 per cent) recorded maximum mycelial inhibition while in case of yeasts, BK5 and BK7 was most effective and significantly superior to all other treatments with 59.72 and 55.56 per cent inhibition in mycelial growth, respectively. Out of botanicals, yeasts and well known fungicides, Yeast BK5 @ 5 per cent was found superior with 94.07 per cent mycelial growth inhibition which was comparable with Mancozeb @ 0.25 per cent. Microbial count of the yeast based foliar sprays was determined to find out the microbial strength of the treatments. Butter milk had more (log10 (CFU/cm2) = 11.26) microbial count followed by Field formulation 2 + Yeast BK5 (10.77) as compared to other bio-formulations. Field evaluation studies referred the application of five foliar sprays of Field formulation 2 + Yeast BK5 @ 5 per cent at 10 day interval started with the inhibition of disease as most efficacious in limiting the Alternaria leaf spot of cauliflower (8 per cent) and enhancing the yield (176.67 q/haEnglishThesis