Jha, P.K.KUMARI, MINA2023-10-192023-10-192021D/PP/389/2018-19https://krishikosh.egranth.ac.in/handle/1/5810199302Aloe vera is an important medicinal plant and widely cultivated in tropical and sub-tropical region. Like other crops it is also attacked by a number of pests and diseases. Among these, black leaf spot is most serious problem in Aloe vera throughout the country resulting in reduction in yield and market value. Its causal organism was isolated and identified as Colletotrichum gloeosporioides (Penz.) Penz. & Sacc. During survey in five districts of North Bihar, highest PDI (32.50%) was recorded in Samastipur while the lowest in Madhepura (22.00%). Five isolates of pathogen obtained from five districts varied in their cultural and morphological features. Pathogenicity test was confirmed by employing Koch‟s postulates. In inoculum density test, the least incubation period (12-14 days) was required at 1.9 x 107 spores/ml followed by 15 days at 2.5 x 106 spores/ml. With increase in concentration of inoculum density, the incubation period was decreased. In course of study, 15 fungal species was recorded with phylloplane and rhizosphere of Aloe vera. The isolates of Rhizopus stolonifer and Penicillium chrysogenum showed their presence in rhizosphere only whereas Curvularia lunata and C. gloeosporioides were recorded only from phylloplane and 11 mycoflora were common in both phylloplane and rhizosphere. When these mycoflora were evaluated for their effect on plant growth promotion in pot experiment, most of them showed growth promoting effect and increased biomass production, whereas C. gloeosporioides, Fusarium solani, Alternaria, Curvularia and Cladosporium sp. showed pathogenic effect and hampered plant growth. The beneficial mycoflora which promoted plant growth in pot condition, were also found effective in suppressing the pathogen in dual culture test. Among them, T. harzianum showed maximum mycelium growth inhibition (76.19%) followed by T. viride (73.59%). In culture filtrate assay, culture filtrate of A. niger was most effective and exhibited 29.40% spore germination, thereby resulted in 63.25% inhibition of spore germination at 5% concentration. The next most effective culture filtrate was that of T. harzianum with 61.8% inhibition of spore germination followed by T. viride (59.49%) and T. asperellum (57.99%). However, culture filtrate of T. harzianum was most effective and inhibited colony growth by 86.90% followed by T. viride (85.76%) at 15% concentration. Out of nine botanicals, the Neem leaf extract was found superior in checking the pathogen growth by 74.82% followed by Tulsi (59.78%) at 10% concentration. Among two molecules tested, carbendazim was most effective and inhibited the pathogen growth by 93.52% followed by azoxystrobin (93.07%) at 250 ppm. In compatibility test, both bioagents (T. harzianum and T. viride) were highly compatible with leaf water extracts of Neem and Tulsi at all the four concentrations. When tested for compatibility with two effective molecules, it was highly compatible with only one molecule i.e., azoxystrobin, and not compatible with other effective molecule carbendazim. During field trial on integrated disease management, the most effective treatment was foliar spray with azoxystrobin @ 250 ppm accompanied with soil drenching of T. harzianum @ 5% which caused 82.63% reduction in PDI. Likewise the foliar spray of azoxystrobin @ 250 ppm accompanied with soil drenching of T. harzianum @ 5% and further foliar spray with Neem extract @ 10% also showed promising disease control (81.40% reduction). The treatment combination having Trichoderma harzianum as a component showed prominent growth promoting effect on plants as evident from the observation in the present study that foliar spray with azoxystrobin @ 250 ppm accompanied with soil drenching of T. harzianum @ 5% and further foliar spray with Neem extract @ 10% recorded maximum plant height (33.12 cm) with maximum number of leaves (10/plant). Likewise soil drenching of T. harzianum @ 5% accompanied by foliar spray with Neem @ 10% also recorded the plant height of 32.02 cm and number of leaves (9.61/plant).EnglishThesis