Effect of Rhizobacteria on Phytophthora meadii, Fusarium oxysporum f. sp. Vanillae and Colletotrichum vanillae Infecting Vanilla

Abstract

Rhizobacterial isolates, Pseudomonas fluorescens (5 isolates), Enterobacter agglomerans (one isolate) and Bacillus spp. (14 isolates), were screened for growth promotion and against rot pathogens of vanilla such as Phytophthora mcadii McRae, Fusarium oxysporum f.sp. vanillae and Colletotrichum vanillae Massae. All the rhizobacterial isolates tested except Bacillus polymixa (isolate IISR909) and one Bacillus sp. (isolate IISR915) were inhibitory to P. meadii to an extent of 74 percent, while F. oxysporum was highly inhibited (91.0%) by Bacillus polymixa (isolate IISR909) in vitro. Bacillus sp. (IISR153) was highly inhibitory to C. vanillae with an inhibition of 77.8%. The maximum growth promotion in terms of shoot length (27cm) in vanilla was observed in plants treated with P. fluorescens (isolate IISR13). Different combination of isolates found promising as growth promoting such as P. fluorescens isolates (I1SR6, IISR853) B. lentus (11SR906) B. polymixa (IISR909) E. agglomerans (I1SR912), Bacillus spp. (isolates IISR910, 11SR913, IISR914, IISR915 and IISR149) as well as suppressing the rot pathogens, viz., P. fluorescens (isolates IISR6, HSRS1, IISR853), Bacillus spp. (isolates IISR147, I1SR148 and IISR152), were tested against root rot of vanilla caused by F. oxysporum f. sp. vanillae. The consortia of rhizobacterial isolates, viz-,1)- P. fluorescens isolates (HSR13, I1SR51), Bacillus sp. (IISRIS2) and B. polymixa (IISR909); 2)- P. fluorescens isolates IISR13, IISR51), Bacillus sp.isolates (IISR148, IISR149, IISR152, IISR 907), B. polymixa (IISR909) and B. lentus (IISR 906); 3) P. fluorescens isolates (IISR6, 1ISR13, IISR51), Bacillus sp. isolates (IISR147, IISR151, IISR1S2, IISR153) and B. polymixa (IISR909); and 4) P. fluorescens isolates (IISR6, IISR5.1, IISR147, IISR148, IISR149 and 1ISR907) and B. lentus (IISR906), gave significant disease reduction (88.22-92.85%) when compared to control. However, among the four rhizobacterial consortia, 3 showed the maximum disease reduction of 92,9%.