Bacteria endemic to saline coastal belt and their ability to mitigate the effects of salt stress on rice growth and yields

Increase in soil salinity adversely affects the metabolism and lowers the yield of rice (Oryza sativa L). Application of plant growth-promoting rhizobacteria (PGPR) to ameliorate the effects of salt stress on sensitive rice can be both effective and sustainable. In this study, 20 bacterial strains were isolated from the soil of saline-prone regions of Satkhira, north of the Sundarbans in coastal Bangladesh. Three bacteria among these grew well in the presence of 3 M salt (NaCl) and were Gram positive and non-motile. Their 16S rRNA sequence revealed that they belong to the Halobacillus genus. Two of them were identified as Halobacillus dabanensis strain SB-26 and the other one as Halobacillus sp. GSP 34. A couple of mechanisms by which these microbes could play beneficial role if associated with plants, such as nitrogen fixation and indole acetic acid (IAA) production, were identified. The two bacterial strains showed positive results for nitrogen fixation and indole acetic acid (IAA) activity under salt stress. Their effect on the physiology and yield of a farmer popular but sensitive BRRI dhan 28 rice variety was investigated under both control and salt stress. At the seedling stage, inoculated plants had significantly greater root length, shoot height, total weight, chlorophyll content, but lower electrolyte leakage both in control and salt stress (0, 40, and 80 mM). Performance of the plants was even better when both bacteria were used in combination. At the reproductive stage, the plants also showed better phenology in presence of the inoculated bacteria. Under stress (50 mM NaCl), these plants showed significantly greater plant height, lower spikelet damage, and yield reduction compared to untreated plants. The identified Halobacillus strains can therefore be used to improve the yield of rice by exploiting their plant growth promotion activities in coastal areas affected by moderate salinity, such as those with an ionic conductivity of up to 5 dS m^?1.