1. KAUTIR (Kerala Agricultural University Theses Information and Retrieval)
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Item Management of fusarium wilt of vegetable cowpea with Consortia of Endophytic Bacilli(Department of Plant Pathology, College of Agriculture, Vellayani, 2024) Anuvinda, A R.; Sreeja, S JThe study entitled “Management of Fusarium wilt of vegetable cowpea with consortia of endophytic Bacilli” was conducted at Department of Plant Pathology, College of Agriculture, Vellayani during 2021-2023 with the objective to evaluate the consortia of endophytic Bacilli for the management of Fusarium wilt of vegetable cowpea. Twenty endophytic Bacillus isolates, sourced from prior studies conducted at the Department of Plant Pathology and the Department of Agricultural Microbiology, were used for the current study. The antagonistic potential of all endophytic Bacillus isolates against Fusarium oxysporum was evaluated through both dual culture plate assay and culture filtrate assay. Out of the 20 isolates, 14 exhibited antagonistic activity against the pathogen. The isolate WL1 stood out, displaying maximum inhibition zone of 7.00 mm against Fusarium oxysporum. Meanwhile, the isolate GR1 achieved the maximum mycelial growth inhibition (30.62%) against F. oxysporum. Culture filtrate of the isolates PCSE8, PCSE10, PNRE4, AR2, AR1, GR1, GR2 and CFLE3 also had inhibitory action against F. oxysporum, indicating antagonism by diffusible metabolites. The findings from direct and indirect antagonism indicated that isolates PNRE5, NAT001, WR2, WR1, VLY17, and PNSE5 did not exhibit antagonistic properties against the wilt pathogen in cowpea. The endophytic Bacillus isolates underwent assessment for various plant growth promoting (PGP) traits, including nitrogen fixation, phosphate solubilization, potassium solubilization, IAA and gibberellic acid production, siderophore production, ACC deaminase activity, ammonia and HCN production, as well as the release of volatile organic compounds. Among the 20 isolates, ten demonstrated nitrogen-fixing capabilities, while 15 exhibited phosphorus solubilizing activity. None of the isolates displayed potassium solubilization, as evidenced by the absence of a clearance zone in Aleksandrov medium. All tested bacterial isolates produced IAA, ranging from 14.64 μg mL⁻¹ to 0.08 μg mL⁻¹. However, none of the isolates demonstrated gibberellic acid (GA) production. Regarding ACC deaminase activity, nine isolates were able to produce α ketobutyrate within the range of 1.35 to 8.303 α-KB μmol. With the exception of four isolates, all tested ones produced siderophore, with the maximum production recorded for CBRE5 at 68.92 μg/ml. Among the 20 isolates, 12 exhibited ammonia production within the range of 5.18 to 0.234 μmol/ml and 11 isolates produced HCN. All isolates tested positive for the production of volatile organic compounds, with PCSE10 demonstrating the maximum mycelial growth inhibition (46.93%) against Fusarium sp. due to the volatile compounds emitted. In the protray growth experiment, there was a significant improvement in all the growth parameters of the seedlings treated with endophytic Bacillus isolates PNRE4, NAT001, AR1, WR2, VLY17, WL1 and PNSE5. Seedling vigour index I values ranged from 3444.80 (AR1) to 1191.00 (GL3) while seedling vigour index II ranged from 92.32 (AR1) to 30.00 (GL3). The compatibility studies among the endophytic Bacillus isolates following disc diffusion method and spot on lawn method indicated that isolates PNRE5, PNRE4, NAT001, AR2, GR1, GR2, WR2, WR1, WL2, PNSE5, CBRE5, CBSE5 and CFLE3 were compatible among themselves. Based on the results of in vitro experiments, eight compatible antagonistic endophytic Bacillus isolates viz., PNRE4, AR2, GR1, GR2, WL2, CBRE5, CBSE5 and CFLE3 with superior plant growth promoting traits and seedling vigour index were pooled together to form Consortium I. All the 20 endophytic Bacillus isolates selected for the study were pooled together to form Consortium II. Seed biopriming for four hours along with soil application of Consortium 1 thrice (@ 20, 40 and 60 DAS) recorded only 33.33% wilt incidence while, the similar mode of application of Consortium II recorded 50 % disease incidence in vivo. The results of field evaluation revealed that seed biopriming for four hours along with soil application of Consortium 1 thrice (@ 20, 40 and 60 DAS) recorded 28% wilt incidence while, the similar mode of application of Consortium II recorded 32 % wilt incidence. No significant difference between Consortium I and II was observed on days taken for flowering, number of pods/plants, pod yield/plant, shoot fresh and dry weight except root fresh and dry weight. The present study emphasizes the importance of assessing the compatibility of strains while formulating a microbial consortium. Therefore, it can be inferred that inoculating cowpea plants with a consortium of compatible antagonistic endophytic Bacillus isolates possessing superior plant growth-promoting traits and seedling vigor index substantially mitigated the occurrence of Fusarium wilt in cowpea. Additionally, it facilitated the improved establishment of plants by enhancing overall plant growth