Identification and in vitro Evaluation of Environmental Stress Resilient Plant Growth Promoting Rhizobacterial Consortia for Rice (Oryza sativa L.)

Abstract

The present study screened bacteria isolated from rice rhizosphere for various beneficial traits related to three categories of plant growth promotion, abiotic stress tolerance, and compatibility with multiple agrichemicals to identify a microbial consortium that performs better than individual isolates in improving rice growth under normal and stressful environmental conditions. Among thirty-two isolates screened, 29, 9, 20 isolates were able to solublilize insoluble minerals of nutrients like phosphorous, potassium and zinc respectively. About 29, 31, 23, 17 isolates were found to possess the traits of IAA, ammonia, siderophore and HCN production respectively. Abiotic stress related traits of salinity, drought and high temperature tolerance were displayed by 8, 2 and 10 isolates respectively when examined for their growth in NaCl (4%, 6% 8%), in PEG (64 g/l equivalent to -0.73Mpa) and at 45℃ temperature. Agrichemical tolerant isolates were identified by screening for compatibility with fertilizers and commonly used rice pesticides. Based on the scores assigned during screening tests, 9 best isolates, three from each category, were selected for development of consortia. Our aim in this initial study was to identify three consortia (C-1, 2 and 3) consisting of three compatible bacteria, and to evaluate their effect on rice seed germination and seedling  growth under normal in vitro conditions. C1 enhanced the growth of rice when compared with individual strains, C2 and C3 with highest vigour index I, II values of 1616 ± 18 and 5.47 ± 0.68 respectively. The 16S rRNA sequence analysis identified the bacterial isolates in C1 as Achromobacter sp, Stenotrophomonas sp and Pseudomonas stutzeri. Therefore, this study has identified a unique consortium that can be used for rice growth promotion while simultaneously demonstrating the advantage of bacterial consortia over single isolate inoculants under non stressed conditions.