Modification of root architecture of rice by guard cell and rhizosphere halotolerant bacteria under saline stress

A significant global issue for agriculture is soil salinity. Rice, being one of the most salt-sensitive cereals, is greatly affected by salinity. High salt concentrations have a detrimental impact on root growth of rice. Halotolerant bacteria are known to alleviate salinity stress and have been shown to alter the root morphology of some plants. This possible alteration effect of halotolerant bacteria on rice is not well known. In this study, the halotolerant bacterial strains Enterobacter cloacae GCH3, Acinetobacter sp. GCH4, Acinetobacter calcoaceticus RSH6 and Bacillus tequilensis RSH8 were used to evaluate the early alterations of rice root architecture. These bacteria were inoculated into rice seedlings growing in culture tubes under gnotobiotic conditions, and root architecture variables of developing roots were assessed periodically using non-destructive 2-dimensional imaging and processing in both normal and salt stress conditions. The images were analyzed and processed to obtain 20 root architecture variables in which, the variables such as maximum number of roots, network solidity, number of lateral roots, network surface area, root thickness, area, volume and bushiness were significantly increased with time course due to halotolerant bacterial inoculation than uninoculated control. The root and shoot biomass was also found to be increased by bacterial inoculation. Number of connecting components, median number of roots, specific root length and major ellipse axes were negatively impacted by halotolerant bacteria. Enterobacter cloacae GCH3 and Bacillus tequilensis RSH8 excelled in most of the traits in improving the root architecture of rice under saline conditions which can promote the early growth stages of root and protect the plant from saline stress effects.