Growth enhancement in vegetable crops by multifunctional resident plant growth promoting rhizobacteria under tropical Island Ecosystem

Plant growth promoting rhizobacteria have been used to improve crop production. A total of 114 bacterial isolates were recovered from the rhizosphere soils of healthy plantation and vegetable crops grown in Andaman Islands. These isolates were evaluated in vitro for plant growth promoting traits, hydrolytic enzyme production and antagonistic activity. Among the isolates, NPB6 and MNB1 were positive to 8 out of 10 properties tested followed by NFB3, MKP3, NNB4 and NTB2. In the dual culture assay, NFB3 showed highest inhibition against the plant pathogen Macrophomina spp (33.3%) and S. rolfsii (23%). Six most promising isolates were selected and identified as Bacillus and Pseudomonas spp. on the basis of Microbial Identification System and 16S rDNA. These isolates significantly increased the seed germination, vigor index, radical and plumule length however, the individual isolates effect varies with crop. All the six isolates enhanced the root and shoot length of brinjal, chilli and okra seedlings while Bacillus cereus (NPB6) in brinjal, B. stratosphericus (NFB3) in chilli and Pseudomonas fluorescens (NNB4) in okra were most effective. The promising isolates can be used in combination with other beneficial native microbes for plant growth promotion even under abiotic stresses and promotion of organic agriculture.    Key words: Biolog, plant growth promotion, rhizobacteria, vegetables.