Biofertilizer development for wheat growth improvement under drought stress and treated wastewater irrigation

This study investigates the impact of indigenous consortia of plant-growth-promoting rhizobacteria (PGPR) on the growth of wheat under drought stress and irrigation with treated municipal wastewater (TMWW). Six strains, identified as the most promising candidates, were used to develop two inoculant consortia. The consortium C1 consists of the PGPR strains Bacillus megaterium FR1.11, Brevibacterium frigoritolerans FR1.38, and Microbacterium azadirachtae FR1.17, while the consortium C2 comprises Bacillus zhangzhouensis O3RR35, Pseudomonas koreensis O3RR25, and Pseudomonas azotoformans O3R15. The two selected consortia significantly improved wheat germination rates (GR), achieving up to 98.3% compared to 60% with single inoculation. The recorded inoculation effectiveness indices of consortium C1 and consortium C2 on wheat growth, denoted as Ic(1,2), indicated that under treated municipal water irrigation, Ic1 ranged from 7 to 85% at 100% field capacity (FC) and from 10 to 44% at 40% FC. On the other hand, Ic2 ranged from 55 to 213% at 100% FC and from 41 to 302% at 40% FC, suggesting a more favorable inoculation effect with consortium C2 compared to C1. Optimal conditions for wheat growth were estimated applying a statistical approach based on the Box-Behnken design (BBD) and response surface methodology (RSM). The considered factors included C2 inoculum size, TMWW and freshwater (FW) ratio, and soil field capacity. The stepwise screening methodology, combined with statistically based experimental designs, led to the development of an efficient consortium (C2) suitable for use as a biofertilizer tailored to semi-arid conditions and wastewater reuse in agriculture, particularly in arid and semi-arid areas.