Plant growth-promoting potential of Bacillus species isolated from the rhizosphere of crops in Sudan and Saudi Arabia

There is an increasing interest in using plant growth-promoting rhizobacteria as alternatives for fertilisers and pesticides in sustainable agriculture. In this study, rhizosphere soil samples from 15 crop species in Sudan and Saudi Arabia were extracted, and 113 rhizobacterial isolates were obtained. Out of eight Bacillus isolates, seven were identified as members of the Bacillus cereus group, which is mainly differentiated by their plasmid-driven phenotypes. The eight strains were tested for their plant growth stimulatory effects on maize (Zea mays L.) and wheat (Triticum aestivum L.) using a model biotest under controlled environmental conditions in a growth chamber. Depending on application form, i.e. viable cells or their culture supernatant, and applied concentrations, six isolates stimulated maize plant growth. Similarly, six isolates enhanced wheat growth, but the influence of the single isolates differed between and within plant species, indicating plant-specific responses. Furthermore, diversity of rhizospheric members of the B. cereus group is highlighted, as all seven isolates differed in terms of colony traits, capacity to produce indole-3-acetic acid, and response by the maize and wheat plants. Overall, this study indicates the potential of plant growth-promoting Bacillus strains for commercial application promoting further investigation in soil and under field applications.