Isolation and characterization of plant growth promoting endophytic bacteria and their effect on tomato (Lycopersicon esculentum) and chilli (Capsicum annuum) seedling growth

The endophytic bacteria known to reside in plant tissues have often been shown to promote plant growth. The present study deals with the efficacy of eight isolates of putative endophytes from surface- sterilized seeds of the crop plants tomato and chilli. Two isolates were Gram negative and six were Gram positive. All isolates were able to grow in up to 6% NaCl, and isolate BETL13 grew in up to 12% NaCl. The isolates were identified using a microbial identification system (Biolog). Of the eight isolates, six belong to the genus Bacillus and two are Serratia. The partial 16S rRNA gene sequences of BECS7, BETS14 shared 99% and 98% similarity with Bacillus sp. BETS11 showed 97% similarity to Bacillus subtilis and BECS1 showed 98% similarity to Arthrobacter sp. Under in vitro conditions, all eight isolates showed antagonistic activity against Sclerotium rolfsii, Fusarium oxysporum, Colletotrichum capsici and Pythium sp. The endophytes were also found to produce indole acetic acid and siderophore and four isolates solubilized inorganic phosphate. The plant growth promotion properties were demonstrated through a chilli- and tomato- based bioassay under greenhouse conditions. Isolates BETL13, BETL9, BECS1, BECL8 and BECS7 showed plant growth promotion in terms of an increase in root and shoot length and the number of secondary roots with respect to their host as well as in cross inoculation.