PADMODAYA, BHASKARAAMRUTHA VEENA, G2020-02-242020-02-242019http://krishikosh.egranth.ac.in/handle/1/5810143466D5873Roving survey was carried out during Kharif 2014 in five districts of Andhra Pradesh for studying collar rot, root rot and stem rot disease incidence. Highest average collar rot incidence (23.00%) was observed in Yerraguntla mandal of Kadapa district, highest average stem rot incidence (19.50%) in Gangadhara Nellore mandal of Chittoor district and highest average root rot incidence (22.00%) in Kadiri mandal of Ananthapur district. Pathogens were isolated from the plants exhibiting typical symptoms of the disease, and pathogenecity test proved Koch postulates. In vitro efficacy of five fungicides viz., thiram, mancozeb, carbendazim, tebuconazole and thiram+vitavax were evaluated against three pathogens using poisoned food technique at five different concentrations. All the five fungicides were effective against A. niger at all the concentrations tested. Carbendazim was ineffective against S. rolfsii at 1000 ppm. Except thiram remaining four fungicides gave 100% inhibition against R. bataticola. A total of fifty Trichoderma isolates were isolated from rhizosphere region of healthy groundnut plants which were designated as Groundnut Rhizosphere Trichoderma (GT-1 to GT-50). When these isolates were screened against S. rolfsii, thirty isolates gave more than 50% inhibition, remaining twenty isolates overgrew over S. rolfsii. When these potential thirty isolates were tested against R.bataticola, Trichoderma isolate-34 (GT-34) showed xx maximum inhibition of growth of Rhizoctonia bataticola (69.44%) followed by Trichoderma isolate-28 (67.78%) and Trichoderma isolate-38 (63.88%). Against A.niger, Trichoderma isolate-28 showed highest inhibition (77.78%) followed by Trichoderma isolate-49 (77.22%) which were on par with each other. The five effective Trichoderma isolates (Trichoderma isolate-9, 28, 34, 38 and 49) showing antifungal activity against pathogens were further evaluated to identify the mechanism of antagonism. Trichoderma coiled around the mycelium of S. rolfsii and R.bataticola penetrated into the mycelium and lysed leading to disruption of cell contents. Volatile and nonvolatile metabolites of five Trichoderma isolates significantly inhibited the mycelial growth of the three pathogens. Among the five antagonists, Trichoderma isolate-9 showed highest inhibition. This isolate highly inhibited the growth of A. niger followed by R. bataticola and S. rolfsii. Least inhibition was shown by Trichoderma isolate-49. Biochemical characterization of potential Trichoderma isolates revealed that more chitinase was produced than β-1, 3 glucanase and cellulose. Uv irradiation was induced for five potential isolates to induce mutations. Five stable mutants were able to inhibit the mycelial growth of three pathogens significantly higher than the wild isolates. In vitro effect of five fungicides were evaluated against wild and mutant Trichoderma isolates. Mancozeb was compatible with both wild and mutant isolates. Remaining four fungicides completely inhibited the growth of Trichoderma isolates. Urea, SSP, MOP and Gypsum had no inhibitory effect against wild and mutant Trichoderma isolates. DAP, 19:19:19, 14:35:14 were relatively incompatible with wild isolate GT-9 at higher concentrations, while the compatibility increased with mutant Trcichoderma. Highest mycelial dry weight was obtained at 300C followed by 250C and 350C. At higher temperatures sporulation was scanty. Trichoderma isolates-9, 34, 38 and 49 were identified as Trichoderma asperellum and Trichoderma isolate-28 as Trichoderma hamatum using ITS primers. OPC-16 primer produced polymorphic band of size 512 bp which was developed as SCAR marker to differentiate wild and mutant Trichoderma isolates. The kharif, 2016 and 2018 field experiment results revealed that seed treatment+soil application (basal)+soil drenching of mutant Trichoderma+mancozeb seed treatment recorded highest germination percentage (91.67), lowest collar rot (3.09%), stem rot (2.74%), root rot incidence (5.49%), highest pod yield (1961.50 kg ha-1) and haulm yield (2573.50 kg ha-1).en-USnullThesis