Optimization of indole-3-acetic acid using response surface methodology and its effect on vegetative growth of chickpea

This study investigates the optimization of various environmental and nutritional factors for the best indole acetic acid (IAA) producing isolate using Box-Behnken Design (BBD) with Response Surface Method (RSM) and examines its effects on early plant growth parameters of Cicer arietinum (chickpea). Firstly, the screening of putative Bacillus isolates based on IAA producing capability and analysis of other plant growth promoting attributes was carried out. The highest IAA producing isolate MRN16 was selected to optimize IAA production based on the BBD and a total of 86 sets of experiments were finalized. The incubation temperature of 35 degrees C, pH of 7.0, incubation time of 8 days, 1.0 g/L tryptophan, 20 g/L starch, 0.5 g/L KNO3, were found the optimal conditions for the maximum IAA production. The extracted or purified IAA was examined by thin layer chromatography (TLC), showed a red colored spot with an 0.75 Rf value. IAA was determined using high-performance liquid chromatography (HPLC) and peak was observed at 6.66 min retention time, comparable with the standard IAA. The greenhouse assay confirmed that MRN16 was a significant isolate for enhancing chickpea vegetative growth parameters such as root/shoot length and weight (fresh/dry). Finally, isolate MRN16 was identified as Bacillus altitudinis using 16S rRNA sequencing. The present research establishes successful use of RSM, as an easy and useful tool to determine the optimized parameters for maximum IAA production in bacteria and further the utilization of bacteria to upsurge the plant growth.