Rhizobacteria Bacillus spp. enhance growth, influence root architecture, physiological attributes and canopy temperature of mustard under thermal stress

In arid and semi-arid regions, high temperature stress is one of the most common abiotic stresses affecting plant growth and development, as well as agricultural output. Growth and establishment of mustard, an important oilseed crop, is affected due to increased incidences of higher-than-normal temperatures during sowing of the crop. In the present study, we screened rhizobacterial isolates for their thermotolerance. Under high temperature stress, three thermotolerant rhizobacterial cultures were assessed for their plant growth promoting activities. There was beneficial effect of high temperature on their indole acetic acid and gibberellic acid production abilities. A pot experiment was conducted to evaluate the effect of the three rhizobacterial strains on mustard growth under high temperature stress. Inoculation with the rhizobacteria significantly improved plant biomass, root architecture and physiological attributes - relative water content, membrane stability index and chlorophyll content. There were lowering of hydrogen peroxide content and lipid peroxidation. Increased total leaf area and lowering of canopy temperature was observed in the inoculated plants, under high temperature. Significant positive correlation was observed between plant biometric traits and most of the physiological attributes, while negative correlation was observed with lipid peroxidation and hydrogen peroxide content. Under both no stress and high temperature stress, response to inoculation with Bacillus sp. strain MRD-17 was markedly more than the other rhizobacterial strains. Thus, these rhizobacteria were able to enhance thermotolerance of mustard during early stages of growth. As a result, thermotolerant rhizobacteria with plant growth-promoting activity can be utilized to alleviate high temperature stress in crops.