Work

Combined application of Azospirillum brasilense and humic acid improves growth, physiology and yield of wheat (Triticum aestivum L.) under tillering-stage drought stress

Year: 2026

Type: article

Abstract: Drought at the tillering stage is one of the most damaging abiotic constraints to wheat ( Triticum aestivum L.) production in arid and semi-arid cropping systems. A field experiment was conducted to evaluate whether the plant growth-promoting rhizobacterium Azospirillum brasilense and the organic soil amendment humic acid, applied singly or in combination, could mitigate the adverse effects of drought stress imposed at the tillering stage. The experiment was laid out in a randomized complete block design with eight treatments and three replications: an untreated control, sole A. brasilense , sole humic acid, and their combination, each evaluated under well-watered and drought-stressed conditions. Drought stress was initiated at tillering (25 days after sowing) by withholding the first irrigation and was maintained for 21 days, after which normal irrigation resumed. Drought stress significantly ( p < 0.01) reduced all measured growth, physiological and yield attributes relative to the well-watered control. Sole application of A. brasilense or humic acid partially alleviated these reductions, but the combined treatment consistently produced the most favorable outcome under both water regimes. Under well-watered conditions, the combined treatment increased plant height, spike length, spikelets per spike, 1000-grain weight, grain yield and biological yield by 13.2, 25.4, 9.9, 10.5, 0.9 and 1.8%, respectively, relative to the untreated control, and it also recorded the highest stomatal conductance, crop growth rate, relative water content and leaf area index. Under drought, the combined treatment (T7) improved grain and biological yieldrelative to the drought control (T4), and its drought susceptibility index for grain yield (0.55) was less than half that of the untreated pairing (1.29), indicating markedly improved drought tolerance. These results indicate that A. brasilense and humic acid act in a complementary manner, whereby microbial phytohormone and nitrogen-fixation activity are reinforced by the water- and nutrient-retention properties of humic acid, and that their combined field application is a practical, low-cost strategy for sustaining wheat productivity under water-limited conditions. Clinical trial registration details: Not applicable.

Source: BMC Plant Biology

DOI: 10.1186/s12870-026-10163-y