Journal of Advances in Microbiology

Background: Cotton, a major global fibre and oilseed crop, is significantly affected by foliar diseases like target leaf spot, causing substantial yield losses. Due to concerns over chemical control, endophytic bacteria offer a sustainable alternative by suppressing pathogens through multiple biocontrol mechanisms.

Aims: To evaluate the efficacy of bacterial endophytes against target leaf spot of cotton under in vitro and field conditions and to identify the most effective endophyte for the eco-friendly management of the disease.

Study Design: All the laboratory experiments were conducted using a Completely Randomized Design(CRD) and field experiment was laid out using a Randomized Block Design (RBD).

Place and Duration of Study: Department of Plant Pathology and Department of Cotton, Tamil Nadu Agricultural University, Coimbatore. August 2023- December 2025.

Methodology: The target leaf spot pathogen was isolated by tissue isolation method and confirmed as Corynespora cassiicola through morphological and molecular characterization. The efficacy of bacterial endophytes against C. cassiicola was evaluated by dual culture technique. The effect of the most effective endophyte namely B. amyloliquefaciens on mycelial growth of observed through Scanning Electron Microscopic (SEM) analysis. The lipopeptide antibiotic genes present in the effective entophytes was identified by PCR amplification using gene specific primers. Furthermore, glass house and field experiments were conducted to evaluate the efficacy of effective endophytes against target leaf spot of cotton.

Results: A total of 10 bacterial endophytes were screened for their antifungal potential against C. cassiicola by dual culture technique under in vitro conditions. Among these, Bacillus amylolquefaciens stand out as a superior endophyte in inhibiting growth of the C. cassiicola by 72.0 per cent. This was followed by B. safensis, B. megaterium and B. subtilis which repressed the growth by 69.1, 68.8 and 64.1 per cent respectively. Scanning Electron Microscopic observation revealed the hyphae of C. cassiicola exhibited morphological abnormalities such as shrinkage, disintegration and lysis when co cultured along with B. amylolquefaciens. The lipopeptide antibiotics genes such as surfactin, iturin and fengycin were detected in B. amylolquefaciens through PCR amplication using gene specific primers. Foliar application of liquid formulation of B. amylolquefaciens @0.5 % twice first at 45 DAS and second at 60 DAS was found to be promising in suppressing the target leaf spot incidence and increasing the yield under both glass house and field conditions. This treatment also promoted the growth by enhancing the root and shoot length of cotton under glass house conditions. Our results demonstrated that, B. amylolquefaciens could be used as an eco-friendly alternative to chemicals for the sustainable management of target leaf spot in cotton.