Plant growth promoting activity of bacteria isolated from Asian rice (Oryza sativa L.) are plant subspecies dependent

Asian rice is one of the most important crops because it is a staple food for almost half of the world’s population. Rice has two subspecies, JAPONICA and INDICA. To have production of rice keep pace with a growing world population, it is anticipated that the use of fertilizers will also need to increase, which may cause environmental damage through runoff impacts. An alternative strategy to increase crop yield is the use of plant growth promoting bacteria. Thousands of microbial species can exist in association with plant roots and shoots, and some are critical to the plant’s survival. We isolated 140 bacteria from rice and investigated whether JAPONICA and INDICA rice subspecies were positively influenced by these isolates. The bacterial isolates were screened for their ability to solubilize phosphate, a known plant growth promoting characteristic, and 25 isolates were selected for further analysis. These 25 phosphate solubilizing isolates were also able to produce other potentially growth-promoting factors. Five of the most promising bacterial isolates were chosen for whole genome sequencing. Four of these bacteria, isolates related to Pseudomonas mosselii, Microvirga sp., Paenibacillus rigui and Paenibacillus graminis, improved root and shoot growth, root to shoot ratio, and increased root dry weights of JAPONICA plants but had no effect on growth and development of INDICA plants. This indicates that while bacteria have several known plant growth promoting functions, their effects on growth parameters can be plant subspecies dependent and suggest close relationships between plants and their microbial partners.