Sustainable management of blister and grey blight diseases of tea using antagonistic and plant growth promoting microbes in Western Ghats of India

The blister and grey blights are the devastating leaf diseases in tea. The severity of blister and grey blight diseases in tea ranged from 22% to 68% and 11.41%–57.02%, respectively in a survey conducted in Southern India during 2022–2023. The morphological and molecular identifications of pathogens revealed that Exobasidium vexans and Neopestalotiopsis clavispora were responsible for causing blister and grey blights on tea in southern India. The conventional management strategy with foliar spray of synthetic fungicides result in fungicidal residue in tea causes environmental pollution and health hazards to human. To overcome this the current study aims to manage the blister and grey blight diseases of tea through the microbial biocontrol agents. The bacterial biocontrol agents viz., Bacillus subtilis (BBV57), Bacillus amyloliquefaciens (TNAU), Pseudomonas fluorescens (Pf1) and the fungal antagonist, Trichoderma asperellum (TV 1) were evaluated for their efficacy against the both blight diseases. All the bio agents have significantly reduced the basidiospore germination and the mycelial growth of E. vexans and N. clavispora, respectively. Among the bio agents, B. amyloliquefaciens registered 88.36% reduction in the germination of E. vexans basidiospore and 85.56% of mycelial growth reduction of N. clavispora in vitro (P < 0.05). Under field conditions the combined soil and foliar application of bacterial antagonists viz., B. subtilis, B. amyloliquefaciens and P. fluorescens each with 1 _˟ 10¹¹ CFU/ml @ 5% concentration at 7 days interval significantly reduced the blister blight incidence with 53.53% & 51.53% reduction over control and 51.53% & 43.65% of reduction over initial during first and second year, respectively. The combined application also reduced the grey blight incidence with 53.53% & 52.00% reduction over control and 56.81% & 47.65% of reduction over initial during first and second year, respectively. This treatments with bioagents were almost comparable with synthetic treatments, such as copper oxy chloride (0.25%) and hexaconazole (0.25%) with 64.63% and 64.76% reduction of blister and grey blight reduction in first year; 59.74%, 51.11% reduction in second year over control (P < 0.05), respectively. Thus, the application of B. subtilis, B. amyloliquefaciens and P. fluorescens can be recommended for the sustainable management of tea blister and grey blight diseases in tea gardens.