REDDI KUMAR, MCHIRANJEEVI, N2021-12-212021-12-212021-12-21D6071https://krishikosh.egranth.ac.in/handle/1/5810179642“INVESTIGATIONS INTO ANTAGONISTIC BASIS OF ROOT ENDOPHYTIC BACTERIA IN THE CONTROL OF CHICKPEA DRY ROOT ROT PATHOGEN (Rhizoctonia bataticola (Taub.) Butler)”A survey was conducted during January, 2017 Rabi season in five major chickpea growing districts of Andhra Pradesh viz., Kurnool, Y.S.R Kadapa, Anantapuramu, Prakasam and Guntur to assess the status of dry root rot incidence under field conditions. Mean maximum dry root rot incidence was observed in Anantapuramu (11.50 %) followed by Kurnool (9.61 %), Y.S.R Kadapa (7.92 %) and Prakasam (7.50 %) and the least was observed in Guntur (6.00 %). Disease occurrence was observed irrespective of cropping system, soil types and cultivars. The disease incidence was low in the irrigated fields compared to rainfed fields. A total of 22 isolates of R. bataticola were obtained and purified by single sclerotial isolation technique. Variability in the cultural and morphological characters of 22 isolates of R. bataticola were studied by growing on potato dextrose agar medium. Among all the isolates CRb 10 taken significantly least time (2.50 days) to occupy the full plate and higher radial growth at 42 hrs was observed with CRb 10 isolate (75.78 mm). However, fluffy colonies were produced by CRb 2 and CRb 15 isolates while, velvety colony texture was observed with CRb 13 and remaining all the isolates showed appressed colony texture. Similarly, out of 22, jet black, light black and grey colour mycelia was observed in total of seventeen, four and one isolates respectively. Among all the isolates, significantly maximum time was taken by CRb 18 isolate for sclerotial initiation and least time was taken by CRb 16 (1.83 days). However, among the isolates higher number of sclerotia per 10 x microscopic field and sclerotial size was observed with CRb 16 (33.33) and CRb 6 (119.32 µm) respectively. Similarly, among 22 isolates, irregular, ovoid and round shaped sclerotia were observed in total of 3, 9 and 10 isolates respectively. Pathogenicity of R. bataticola isolates was proved by soil inoculation method. When observations were collected on disease incidence (%), among the isolates tested maximum disease incidence (100 %) was observed in CRb 9 and it was considered as a most virulent pathogen isolate and used for further studies. A total of 40 antagonistic endophytic bacteria were isolated from healthy roots of different chickpea varieties and the antagonistic efficiency was tested using dual culture technique. Among the isolates CREB 37 showed maximum antifungal efficiency with 74.04 % inhibition against virulent R. bataticola isolate CRb 9. Based on the results it was considered as a potential isolate and used for further studies. Mannitol @ 2 %, soytone @ 2 % pH 7 and temperature 30oC were found to be optimum for cell growth and antibiotic production. Similarly, significant improvement in the cell growth and antibiotic production was observed with the modified Luria broth than the basal medium (Luria broth). Crude antibiotic substances were extracted and tested their bio-efficacy against R. bataticola by agar well diffusion assay. Among the different concentrations tested significantly higher inhibition was recorded at 100 µl (77.23 %). The microscopical examination of the crude antibiotic extract treated mycelia of the R. bataticola revealed its effect on the fungal morphology. Light microscopic analysis revealed that severe mycelial destruction and the SEM images clearly explained the disruption of the fungal hyphae due to the mechanistic effect of antibiotic compounds on fungal cell wall. Among the 14 potential isolates, Gram negative (7) and Gram positive (7) were recorded in equal proportion and all were rod shaped bacteria. Out of the 14 isolates, a total of 9, 7, 2, 1, 2, 3, 3, 13, 6, 3 and 0 showed positive for amylolytic activity (starch hydrolysis), proteolytic activity (Gelatin hydrolysis), lactose utilization, indole production, methyl red test, Voges-Proskeur test, citrate utilization, presence of catalase activity, ammonia production, HCN production and siderophore production respectively. 16S r DNA sequence analysis was used to identify the potential bacterial isolates such as CREB 9, CREB 21 and CREB 37 and which were exhibited close similarity of 97.75, 98.48 and 93.28 per cent with Enterobacter cloacae, Pseudomonas aeruginosa and Bacillus subtilis respectively. Talc based formulation of potential endophytic bacterial isolate B. subtilis (CREB 37) was prepared and tested the bio-efficacy of formulation and crude antibiotic extract in pot culture. Under glasshouse conditions treatment T7 (seed treatment with potential bacterial antagonist (talc formulation) @ 10 g kg-1 + soil application with talc based formulation of potential bacterial antagonist @ 100 g pot-1) was found to be superior as it recorded maximum germination per cent, plant height, root length, dry weight and least per cent disease incidence compared to other treatments.EnglishThesis