Abstract
Cowpea, an annual legume, suffers from several disease symptoms caused by Macrophomina phaseolina. Rhizobacteria isolated from pesticide infested soil, identified by blast analysis as Bacillus cereus, Bacillus safensis, Pseudomonas donghuensis and Pseudomonas aeruginosa ascertained tolerant to at least 0.1% pesticides viz. methomyl, imidacloprid and carbendazim. In vitro antagonism against pathogen exhibited maximum by P. aeruginosa 63%. All rhizobacteria were bestowed with attributes responsible for pathogen control and plant growth promotion. Field evaluation resulted highest 75% disease control, enhancement of length, nodule counts, biomass or yield per plant by P. aeruginosa. All rhizobacteria induced systemic resistance in cowpea under challenged inoculation with pathogen by augmenting defensive enzyme production. Highest Phenylalanine Ammonia Lyase activity was expressed in P. aeruginosa treated plants 1.02 μMoles/ml/min, Polyphenol Oxidase by P. donghuensis 1.39 μMoles/ml/min, Chitinase by B. cereus 0.745 μMoles/ml/min and 400 percent relative activity of Peroxidase by P. aeruginosa. The rhizobacteria were prospective for plant disease control, growth promotion and as immunity boosters in pesticide and heavy metal infested toxic environment.
Highlights
Cowpea (Vigna unguiculata (L.) Walp.), an annual legume, is among the earliest known human food sources (Chevalier, 1964) and supposedly the principal ancient pulse crop of India
Rhizobacterial isolates Tn-1, Tn-4, D1, and Tn 6 were pesticide tolerant at different concentrations (Bandopadhyay et al, 2018) apart from Bacillus cereus (NCIM 5557) and Bacillus safensis (NCIM 5558) (Roy et al, 2018) which were considered as reference strains
All the bacterial isolates used in the current study showed negative result in blood agar medium and were non pathogenic strains
Summary
Cowpea (Vigna unguiculata (L.) Walp.), an annual legume, is among the earliest known human food sources (Chevalier, 1964) and supposedly the principal ancient pulse crop of India. The plant fixes atmospheric nitrogen @ of 56 kg per ha in soil, with root nodule inhabiting symbiotic bacteria (Ahlawat & Shivkumar, 2005) as well as enriches soil microbial population. As food legume, it is rich dietary source of 24.8 percent protein, 63.6 percent carbohydrate, 1.9 percent fat, 6.3 percent fibre, 0.00074 percent thiamine, 0.00042 percent riboflavin and 0.00281 percent niacin (Davis et al, 2000).
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