Fusaricidin produced by the rhizobacterium Paenibacillus polymyxa NX20 is involved in the biocontrol of postharvest plant-pathogenic oomycete Phytophthora capsici

Abstract

Phytophthora capsici is a destructive oomycete pathogen that mainly threatens solanaceous and cucurbitaceous vegetable crops, resulting in severe economic losses annually. Paenibacillus polymyxa, a typical biological control agent (BCA), has been widely used to control plant diseases due to its efficacy and environmentally friendly properties. However, the application of P. polymyxa to control pathogenic oomycete P. capsici during the postharvest period has not been reported. In this study, we found that P. polymyxa NX20 exhibited the best inhibitory effect on the mycelial growth of P. capsici among 160 cultivable isolates, and the lipopeptide fusaricidin was the main factor in its antagonistic action. Fusaricidin exhibited good inhibition activity against P. capsici with an EC50 value of 2.46 mg L−1. Both zoospore production and germination were suppressed by fusaricidin in a dose-dependent manner. According to the microscopy observation and cell membrane permeability assay, fusaricidin was proved to impaired the plasma membrane structure and led to cell death in P. capsici. Additionally, after exposure to fusaricidin, the reactive oxygen species accumulation was induced and DNA/protein synthesis was inhibited in P. capsici. RNA-Seq analysis revealed that fusaricidin treatment could potentially affect plasma membrane integrity, transmembrane transport, energy metabolism, and signal transduction in P. capsici. Furthermore, fusaricidin exhibited good control efficacy against P. capsici on watermelon, pepper, and cherry tomato fruit. Overall, these findings elucidated the anti-oomycete mechanism of fusaricidin and highlighted the potential of P. polymyxa strain NX20 on vegetable protection and preservation.