Paenibacillus polymyxa K17 Controls Leaf Spot of Tea Plant by Impairing Fungal Cellular Structure and Energy Metabolism

Utilizing biocontrol microbes has emerged as a promising strategy for sustainable disease management in tea cultivation. Here, a novel strain Paenibacillus polymyxa K17 was isolated, which possesses broad-spectrum antifungal capacity against 14 phytopathogens from multiple crops, with inhibition rates of 53–82%. Notably, P. polymyxa K17 demonstrated comparable or occasionally superior control efficacy to the fungicide kasugamycin in leaf spot disease caused by Lasiodiplodia gonubiensis across three tea cultivars. P. polymyxa K17 induced mycelial deformation and cellular damage of L. gonubiensis. Meanwhile, strain K17 metabolites markedly suppressed the gene expression in multiple pathways related to fungal energy metabolism, including oxidative phosphorylation, TCA cycle, and pyruvate metabolism. Correspondingly, the activities of the mitochondrial complex and the levels of ATP and pyruvate in L. gonubiensis were markedly decreased. These findings indicate that P. polymyxa K17 inhibits fungal growth by disrupting energy metabolism and cellular structure, highlighting its potential for controlling multiple fungal diseases in tea gardens.