Biohardening of micropropagated banana using endophytic bacteria to induce plant growth promotion and restrain rhizome rot disease caused by Pectobacterium carotovorum subsp. carotovorum

Abstract

Abstract Pectobacterium carotovorum subsp. carotovorum is a serious pathogen which causes soft rot or rhizome rot or tip over disease of banana in the tropical and subtropical regions of India. Rhizome rot disease incidence was severe during the secondary hardening stage in the micropropagated plantlets; prominently in the cv. Grand Naine (AAA) cultivars, effecting the initial establishment of banana plantlets in the main field. In order to combat rhizome rot disease, an experiment was conducted on biohardening of the micropropagated banana plantlets. Thirty bacterial isolates from the endophytic regions of banana were analyzed using 16S rRNA and the effective strains were identified as Bacillus subtilis. PP and CL3 strains of B. subtilis were observed to inhibit the growth of bacterial pathogen on nutrient agar. Further, crude metabolites from effective B. subtilis strains (PP and CL3), were inhibited the growth of bacterial pathogen. The endophytic Bacillus subtilis were used for biohardening of the micropropagated banana plantlets cv. Grand Naine (AAA) during the primary and secondary hardening stages. Biohardening of banana plantlets with endophytic B. subtilis significantly suppressed rhizome rot disease when treated with two strains of B. subtilis (PP and CL3) assoil application during the time of planting. Application of bacterial endophytes resulted in an increase in plant growth promotion activities viz., plant height, pseudostem girth, number of leaves and leaf area. Increased activity of defense enzymes like peroxidase (PO), polyphenol oxidase (PPO), phenylalanine ammonia lyase (PAL), phenolic content and PR proteins; chitinase and β-1,3-glucanase was observed in the biohardened plants that were inoculated with the bacterial antagonist.Thus, the present study demonstrated that biohardened micropropagated banana plantlets with endophytic B. Subtilis mediate the induction of systemic resistance against pathogens and could therefore be used as potential biological control agents for rhizome rot disease of tissue culture banana cv. Grand Naine (AAA).