Bioactivity and mechanisms of Ewingella americana for the control of Alternaria leaf spot on peanut

From the paper

Abstract

Bacterial biocontrol agents are emerging as a suitable alternative for the management of fungal diseases, avoiding the use of toxic fungicides. Commercial biocontrol currently relies heavily on the well-known genera Bacillus and Pseudomonas; however, there is a critical need to discover and characterize novel bacterial agents with unique ecological niches and modes of action. Although Ewingella americana is a bacterial mycoparasite that causes black rot in various edible mushrooms, such as Agaricus bisporus and Pleurotus ostreatus, its potential use for the management of fungal diseases remains completely unexplored. In this study, Alternaria alternata was identified via morphological analysis and ITS, EF1-α, and GADPH sequencing as the causal agent of leaf spot in peanut plants in Nantong, China. Interestingly, a new E. americana strain, NJC80, was found coexisting with A. alternata in symptomatic peanut leaves. NJC80 inhibited A. alternata mycelial growth and spore germination, and exhibited a variety of antifungal mechanisms, including production of antifungal metabolites, competition for nutrients, and mycoparasitism. In plant growth chamber, preventive application of 1 × 10⁸ cells/mL NJC80 reduced Alternaria leaf spot disease index in peanut leaves by 76.3 %, showing higher efficacy than the commercial fungicide tebuconazole, 56.9 % inhibitory efficacy. Preventive application of 1 × 10⁸ cells/mL NJC80 reduced Alternaria leaf spot disease index in a peanut field by 85.9 %. This is the first report on the use of E. americana for biocontrol purposes, revealing its potential as a novel bacterial biocontrol agent for fungal disease management.