Dr. V. MANOJ KUMARM. ADITHYA2024-09-282024-09-282024-09-27D6641https://krishikosh.egranth.ac.in/handle/1/5810215201Maize (Zea mays L.) is the third most important cereal crop grown in India after rice and wheat. Yield potential of maize is mainly affected by various biotic and abiotic stresses. It is attacked by a wide range of foliar and stem diseases at different growth stages. Among the various foliar diseases affecting maize, Turcicum leaf blight caused by Exserohilum turcicum (Pass.) Leonard and Suggs. is the most destructive and prevalent disease causing significant yield loss. Keeping in view of importance of this disease, studies were conducted on the prevalence of the disease in major maize growing mandals of Guntur district of Andhra Pradesh during rabi, 2020-2021. Survey in Guntur district revealed 31.53% of Turcicum leaf blight incidence incited by the fungus E. turcicum. Among the surveyed mandals, the highest disease incidence of 33.65% was recorded in Chebrolu mandal and least disease incidence of 29.55% was recorded in Duggirala mandal. As many as 35 methylotrophic bacterial isolates were isolated from the rhizospheric and phyllospheric ecosystem of maize and their morphological and cellular characterization was done. Morphologically most of them were light pink coloured, round shaped, smooth textured opaque colonies with entire margin and convex elevation. Microscopic studies revealed that most of them were single rod shaped Gram negative cells. Dual culture technique was carried out to evaluate the antagonistic potential of methylotrophic isolates against E. turcicum. The test pathogen was significantly inhibited by all 35 methylotrophic bacterial isolates tested. Five isolates viz., PPM 2, PPM 4, PPM 6, PPM 8 and PPM 13 were found to be the the most promising antagonists among all isolates with mycelial inhibition of 63.12, 61.67, 60.95, 59.68 and 59.42 per cent respectively. Microscopic examinations of the interaction zone revealed distinctive morphological changes in the fungal mycelium, including hyphal thinning, shortening xiv of hyphal septa, swelling, wrinkling, protoplasm disintegration, clustering of hyphae and hyphal tip shearing. Sealed plate experiment was carried out to evaluate the ability of methylotrophic isolates to produce volatile organic compounds. Among all the tested isolates, PPM 2 was found to be superior in volatile production with the appearance of restricted growth of fungal mycelium at their periphery during all hours of incubation followed by PPM 4, PPM 6, PPM 8 and PPM 13. Change in colour of the fungal mycelium from black to white due to the action of volatiles was also noticed. Physiological characterization of the five potential methylotrophic isolates revealed that neutral to alkaline pH ranging from 7 to 9 support maximum growth of methylotrophic bacteria and optimum growth occurs at pH 7. In case of salt tolerance, methylotrophic isolates exhibited maximum growth at 2.5 % NaCl concentration. The growth was decreased with increasing concentration. All methylotrophic isolates showed variable response to antibiotics. All the five potential methylotrophic isolates were tested positive for biochemical characters such as utilization of nitrogen sources, production of protease, amylase, catalase and siderophores whereas, only PPM 2, PPM 4 and PPM 8 poduced auxin. PPM 2 and PPM 8 were found positive for HCN production while PPM2 and PPM 4 exhibited phosphate and potash solubilizing actvity. All of them showed a negative reaction for ONPG, H2S production, methyl red and phenyl alanine deamination. The plant growth promotional ability of methylotrophic bacteria was evaluated under pot culture without pathogen inoculation. All the potential methylotrophic isolates significantly improved shoot length, root length and germination percentage of maize seedling over un-inoculated pathogen control and Mancozeb check. The treatment 7 where co-inoculation of all five potential methylotrophic isolates was done, was found to be superior over all other treatments in enhancing germination, shoot length, root length and vigour index of plants. Effect of methylotrophic isolates in plant growth promotion of maize under pathogen stressed condition was assessed after seed treatment followed by two foliar sprays with antagonists. Co-inoculation of all five methylotrophic isolates was found to be significantly superior over all other treatments in enhancing shoot length, root length, leaf length and leaf width at 60 days after sowing. Among different treatments employed for management of Turcicum leaf blight under green house conditions, treatment 8 where co-inoculation of all five potential methylotrophic isolates was done, was found to be superior in disease control with 46.68% inhibition over control which was found to be on par with the disease reduction by the chemical check.EnglishThesis