Lower Frequency and Diversity of Antibiotic-Producing Fluorescent Pseudomonads in Rhizosphere of Indian Rapeseed–Mustard (Brassica juncea L. Czern.)

Abstract

Fluorescent pseudomonads are one of the most important microbial communities which play a key role in rhizosphere to enhance plant growth-promotion and protection. The diverse groups of antibiotics viz. 2,4-diacetylphloroglucinol (DAPG), phenazine-1-carboxylic acid (PCA) and pyoluteorin (PLT) are produced by fluorescent pseudomonads inhibiting growth of fungal pathogens which results in health upliftment of plants. The present study, discusses about frequency and diversity of 138 antibiotic-producing fluorescent pseudomonads isolated from eight genotypes of rapeseed mustard rhizosphere (Brassica juncea L. Czern.). The plant growth promoting traits and antibiotics (DAPG, PCA and PLT) production of isolates were examined by using polymerase chain reaction (PCR), thin layer chromatography (TLC) and dot blot-hybridization. Among 138 isolates, 47, 25 and 9 % of isolates were positive in indole production, phosphate solubilization and antagonism potential against Sclerotinia sclerotiorum (causal agent of white mold disease in rapeseed mustard), respectively. PCR amplifications showed that none of the isolates had phlD (DAPG) and phzC (PCA) genes, but four isolates (UKA-2, UKA-8, UKA-11, UKA-66) had pltB (PLT) gene, which was further confirmed by TLC and DNA dot-blot hybridization. BOX profiles of pltB positive isolates were distinct, showing unique genetic diversity in the small population. The four pltB positive fluorescent pseudomonad isolates could be used as promising bio-control and plant growth-promoting inoculants for Indian rapeseed mustard.