Antifungal activity of the culture filtrate of Chaetomium subaffine LB-1 against Bipolaris maydis and its underlying interaction mechanism

Abstract

Objective Chaetomium subaffine LB-1 is a biocontrol strain identified in our laboratory. This study aimed to determine the antifungal activity of the culture filtrate of C. subaffine LB-1 against Bipolaris maydis and elucidate the pathogen response mechanism. Methods Antifungal activity of the culture filtrate of C. subaffine LB-1 was assessed using a poison plate assay and a potted maize plant assay. The interaction mechanism between the culture filtrate and pathogen was further investigated through morphological observation, cell membrane permeability detection, and transcriptome analysis. Results In vitro assays revealed that the culture filtrate of C. subaffine LB-1 significantly inhibited the growth of B. maydis , induced hyphal swelling and impaired cell membrane permeability of the pathogen. The potted maize plant assay confirmed the antifungal activity of the culture filtrate, achieving a control efficacy of 71.34% against southern corn leaf blight. RNA-seq analysis identified 4,124 differentially expressed genes (DEGs) in B. maydis treated with the culture filtrate (Bip_LB) compared with the untreated control (Bip_CK), including 1,924 upregulated and 2,200 downregulated genes. Combined gene function and metabolic pathway analyses of the DEGs indicated that genes associated with transmembrane transporter activity, carbohydrate degradation, amino acid degradation, DNA replication, and RNA synthesis and processing were significantly downregulated. In contrast, genes involved in phospholipid degradation, the pentose phosphate pathway, detoxification metabolism, and drug efflux were significantly upregulated. Conclusion The culture filtrate of C. subaffine LB-1 exhibited strong antifungal activity and pronounced mycolytic effect against B. maydis . It impaired cell membrane permeability and cellular nutrient uptake, resulting in reduced carbohydrate and amino acid degradation and inhibited cell proliferation in B. maydis . Correspondingly, nutrient and energy compensation through lipid degradation and the pentose phosphate pathway, along with detoxification-related activities, were activated in B. maydis upon exposure to the culture filtrate of C. subaffine LB-1. These findings provide insights into the antifungal activity of the culture filtrate of Chaetomium species and support the application potential of the culture filtrate of C. subaffine LB-1 in management of southern corn leaf blight.

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