The Effect of Growth Promoting Bacteria on Barley Yield and Morphological Root Characteristics Under Different Water Conditions

Under water stress conditions, growth-promoting rhizobacteria could alter root characteristics, leading to increased plants yield. A controlled experiment with two barley cultivars, Dasht, and Kavir, was carried out with four inoculations of Bacillus simplex strains (31-2, 42-3, 51-4, and control), in two irrigation levels of 80 and 50% of field capacity. The results showed that inoculation with the mentioned bacteria increased the biological yield of barley by 28% under water stress condition compared to the control treatment. The effect of bacteria was cultivar dependent. B. simplex 31-2 had the most significant effect on the biological yield of Kavir cultivar, and B. simplex 42-3 on the Dasht cultivar. Linear relationships between root characteristics and barley's biological yield were observed. The highest coefficients of determination (R2) were obtained with fresh root weight (84%), root volume (83%), and root surface (81%). Considering the relationship between root traits and the biological yield of barley and the role of B. simplex 31-2 in a 121% increase in root area under water stress, it seems that this trait is the essential mediator of yield. Due to the insignificance effect of B. simplex 3-32 on the root characteristics, against the increase of shoot performance by this bacterium, its mode of action may be due to inducing improvement on other physiological pathways. Overall Bacillus bacteria are effective in mitigating the negative effect of water stress on barley and these bacteria can be considered effective candidates for the production of biofertilizers.