Rhizobacterial diversity exhibiting biotic stress tolerance in association with wheat-cotton crop rotation: Implications for plant-microbe interactions and agroecosystem resilience.

Biotic stress, particularly from fungal diseases, significantly impedes agricultural productivity worldwide. To meet the increasing demand for sustainable food production, environment-friendly and cost-effective solutions are needed. Plant growth-promoting rhizobacteria (PGPR) provide a sustainable alternative by enhancing plant health and acting as biocontrol agents. This study aimed to investigate the genetic diversity and biocontrol potential of biotic stress-tolerant rhizobacteria isolated from the rhizosphere of cotton and wheat plants infected with fungi in a cotton-wheat rotation area. A total of 136 rhizobacteria were isolated and screened for their in-vitro antifungal activity against Fusarium oxysporum. Among these, 108 isolates demonstrated antifungal activity against F. oxysporum. Additionally, various biocontrol-linked traits were assessed, including hydrogen cyanide (HCN) production, starch hydrolysis, exopolysaccharide (EPS) production, enzyme production (pectinase, protease, gelatinase, catalase) and biofilm formation. The results showed that 88 isolates exhibited pectinase activity, 105 showed biofilm formation and EPS production, 20 demonstrated protease production, 93 showed starch hydrolysis activity. Only three isolates produced hydrogen cyanide. Gelatinase activity was observed in 124 isolates, while catalase activity was detected in 87 isolates. Genetic diversity analysis of the tolerant rhizobacteria was performed using REP, ERIC, and (GTG)₅-PCR fingerprinting. The dendrogram constructed from (GTG)₅ and REP-PCR fingerprint profiles indicated greater diversity. Moreover, all three PCR-primers effectively differentiated the cotton rhizosphere isolates from those obtained from the wheat rhizosphere, indicating a distinct resident bacterial community despite the cotton-wheat rotation. These findings suggest the presence of diverse, biotic stress-tolerant rhizobacteria in the cotton-wheat rotation area, which could be utilized as potential biocontrol agents against fungal plant diseases. However, further research is required to explore the pathways underlying their antifungal potential and to develop sustainable and efficient bio-formulations for field applications.