Selection of Chickpea-Rhizosphere-Competent Pseudomonas fluorescens NBRI1303 Antagonistic to Fusarium oxysporum f. sp. ciceri, Rhizoctonia bataticola and Pythium sp.

Abstract.

A procedure that consumes less screening time was developed for screening chickpea rhizosphere-competent bacteria for suppression of the chickpea pathogenic fungi Fusarium oxysporum f. sp. ciceri, Rhizoctonia bataticola and Pythium sp. Of the 478 bacteria obtained by random selection of the predominant, morphologically distinct colonies, 386 strains that effectively colonize chickpea roots could be divided broadly into three different groups. The first group consisted of 44 good chickpea rhizosphere colonizers with 10⁷ to 10⁸ colony-forming units (CFU)/g root; the second group consisted of 253 medium chickpea rhizosphere colonizers with 10⁴ to 10⁶ CFU/g root; and the third group consisted of 89 poor chickpea rhizosphere colonizers with 10⁰ (nondetectable) to 10³ CFU/g root. Forty-four Rif^r strains from the first group of good chickpea rhizosphere colonizers were further screened for their in vitro biocontrol activity against F. oxysporum f. sp. ciceri, R. bataticola, and Pythium sp. One bacterial strain was selected for further work because of its unique ability to inhibit all three fungi and its good chickpea rhizosphere colonization ability. This is the first report of a single biocontrol bacterium active against three most devastating pathogenic fungi of chickpea. In a greenhouse test, chickpea seed bacterization with P. fluorescens NBRI1303 increased the germination of seedlings by 25%, reduced the number of diseased plants by 45%, compared with nonbacterized controls. Increases in seedling dry weight, shoot length, and root length ranged from 16% to 18%. Significant growth increases in shoot length, dry weight, and grain yield, averaging 11.59%, 17.58%, and 22.61% respectively above untreated controls, were attained in field trials in Agra and Jhansi. A rifampicin-resistant mutant P. fluorescens NBRI1303R of the P. fluorescens NBRI1303, used to monitor chickpea root colonization, confirmed the rapid and aggressive colonization by the bacterium, making it a potential biocontrol agent against chickpea phytopathogenic fungi. The results, demonstrating an increase in the efficiency of screening and detection of plant beneficial strains, should greatly benefit future studies.