Genotyping antibiotic producing fluorescent pseudomonads to select effective rhizobacteria for the management of major vanilla diseases

The genotypic diversity that occurs in antagonistic microorganisms provides an enormous resource for improving biological control of plant diseases. In this study, the diversity of 2,4-diacetylphloroglucinol (DAPG) and phenazine-1-carboxylic acid (PCA) producingPseudomonas sp. from different vanilla plantations of three different regions were studied. Out of eighty-five isolates of rhizobacteria from native soils of vanilla plantations, forty-four were positive to PCR amplification of a 560 bp fragment, which is specific of the genusPseudomonas. Among the forty-four isolates, twenty-one exhibited more antimicrobial activity against fungal pathogensviz., Fusarium oxysporum f. sp.vanillae (Tucker) Gordon,Phytophthora meadii McRae andColletotrichum vanillae underin vitro conditions. Twenty-one and sevenPseudomonas showed positive amplification for DAPG and phenazine respectively. An analysis of the level of biodiversity with DAPG and PCA producers at the species level was performed by comparing the restriction patterns of the genus specific 16S–23S ribosomal DNAs (rDNAs) amplified by PCR. This allowed us to cluster the isolates into four different amplified rDNA restriction analysis (ARDRA) groups. Eventually, it was found that some of the DAPG and PCA producers, which originated from different locations, fall under the same cluster. Bacterisation of vanilla plants with antibiotic producing fluorescent pseudomonads isolates resulted in a significant reduction of major diseases in vanilla both in glasshouse and field conditions.