New Bacillus subtilis Strains Isolated from Prosopis glandulosa Rhizosphere for Suppressing Fusarium Spp. and Enhancing Growth of Gossypium hirsutum L.

SIMPLE SUMMARY: Fusarium species can cause serious damage to agricultural crops. Due to the significant losses in crop production along with the harmful effects of the chemical control of plant diseases on human health and the environment, the use of biocontrol agents for the efficient control of Fusarium spp. is becoming an important issue. In the present study, three bacillus subtilis strains (LDA-1, LDA-2, and LDA-3) were examined for their potential to promote cotton growth and act as biocontrol agents against Fusarium spp. All Bacillus strains exhibited defensive effects in cotton plants against phytopathogenic Fusarium spp. The results suggest that the antagonism mechanism of Bacillus strains against phytopathogenic Fusarium spp. could be due to the ability of bacterial strains to produce lipopeptides and other molecules with antifungal activities. In conclusion, these Bacillus subtilis strains can be promised as biocontrol agents, especially in organic and sustainable agricultural systems, and can reduce the extensive use of toxic chemical pesticides in agricultural system. ABSTRACT: Rhizobacteria from desert plants can alleviate biotic stress and suppress plant diseases, and consequently can enhance plant growth. Therefore, the current study was performed to isolate and identify Prosopis glandulosa-associating rhizobacteria based on their antagonistic activity against Fusarium species and plant growth-promoting properties. Three bacterial isolates were identified as Bacillus subtilis: LDA-1, LDA-2, and LDA-3. The molecular analysis suggests the biosynthesis of the bacteriocins subtilisin and subtilosin, as well as the lipopeptide iturin, by these strains. In addition, the antagonistic study by dual-culture assay showed a high efficacy of all B. subtilis strains against phytopathogenic fungi (Fusarium nygamai, F. equisseti, F. solani, F. solani ICADL1, and F. oxysporum ICADL2) with inhibition percentages ranging from 43.3 to 83.5% in comparison to the control. Moreover, atomic force microscopy (AFM) analysis showed significant differences in the cell wall topography of the F. solani ICADL1 among the treated mycelia and untreated control. As a result, these three B. subtilis strains were used as bioinoculants for cotton seedlings infected by F. solani ICADL1 in pot trials, and the results revealed that the bacterial inoculations as an individual or combined with F. solani ICADL1 significantly improved cotton root and stem length, lateral roots, indole acetic acid (IAA), and gibberellic acid (GA(3)) contents, as well as increased antioxidants, flavonoids, and phenols in comparison to those obtained from healthy and infected control plants. In conclusion, the three bacterial strains of B. subtilis (i.e., LDA-1, LDA-2, and LDA-3) are considered promising tools as biocontrol agents for F. solani and cotton growth promoters, and consequently can be used as bio-ertilizer in sustainable agriculture systems.