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Acharya N G Ranga Agricultural University
A total of 40 isolates, 20 of Pseudomonas fluorescens and 20 methylotrophic bacteria were isolated from the blackgram phyllosphere and their biochemical studies revealed that all the P. fluorescens isolates tested to be positive for Catalase, Amylase, Urease and Protease activity. 17 out of 20 isolates had Siderophore production and only two isolates has HCN production. Only one isolate had shown positive for indole production. All the PPFM isolates were found positive for Catalase and Urease activity and negative for HCN production. Fourteen out of 20 PPFM isolates had shown Amylase activity, only one isolate shown positive for Protease activity and two had shown positive for Siderophore production. Testing for PGP traits revealed that 15 P. fluorescens isolates had shown Psolubilization, six isolate had shown IAA production and five isolates had shown Ksolubilization. Eleven PPFM isolates had shown positive for P- solubilization and only one isolate had shown positive fir IAA production and all the PPFM isolates had shown negative for K- solubilization. In vitro dual culture studies revealed that, among 20 P. fluorescens isolates tested, two isolates viz., CBP- 05 and PPP-01 were found to be the most promising isolates with maximum antagonistic potential against Corynespora cassiicola (66.51% and 64.99%) and Alternaria alternata (60.43% and 60.43%). Two methylotroph isolates viz., PPM-01 and ABM-04 exhibited maximum antagonistic potential against C. cassiicola (68.04% and 54.34%) and A. alternata (34.55% and 34.55%). xvii Intra and inter compatibility studies of four antagonistic bacterial isolates, viz., two Pseudomonas (CBP-05, PPP-01) and two methylotrophs (PPM-01 and ABM-04) revealed that all the isolates were compatible with each other under in vitro conditions which was tested through cross streak method. Based on 16S rRNA gene sequencing the Pseudomonas isolate PPP-01 and CBP-05 was found closely related with Pseudomonas fluorescens. However, the methylotroph PPM-01 grouped with Methylobacterium indicum and ABM-04 grouped with Hyphomicrobium facile. The pathogens Corynespora grouped with Corynespora cassiicola isolate while Alternaria was related with Alternaria alternata isolate. Under field conditions, Fungicidal check had shown lowest PDI and AUDPC against Corynespora leaf spot (28.11% and 501.10 respectively) and Powdery mildew (0.00% and 0.02 respectively) and there was a significant increase in yield (1130.40 kg ha-1), number of pods per plant (20.10), no. of seeds per pod (5.63) and test weight of 3.85g. Among the antagonist treated plots, foliar spray of consortium of CBP-05, PPP- 01, PPP-01 and ABM-04 @ 108 CFU ml-1 has recorded the lowest PDI against Corynespora leaf spot (36.37%) and Powdery mildew (38.17%) and minimum area under disease progress curve for both Corynespora leaf spot (639.03) and Powdery mildew (644.33). It was also observed to significantly increase the number of pods per plant (19.50), No. of seeds per pod (5.43) and the highest test weight of 3.77g, yield of 1080.25 kg ha-1. However, the benefit cost ratio (BCR) of the different treatments varied from 0.99 to 1.70 with the highest BC ratio was recorded with Treatment T7 (CBP-05, PPP- 01, PPP-01 and ABM-04 (FS)) (1.70) and the fungicide treatment having BC ratio of 1.55 which represents, the combination treatment is a potential alternative to fungicides