Suppression of Sclerotinia sclerotiorum by the Induction of Systemic Resistance and Regulation of Antioxidant Pathways in Tomato Using Fengycin Produced by Bacillus amyloliquefaciens FZB42

Abstract

Lipopeptides from <i>Bacillus</i> species exhibit promising biological control activity against plant pathogens. This study aimed to explore the potential of purified fengycin to induce systemic resistance in tomato against <i>Sclerotinia sclerotiorum</i>. <i>Bacillus amyloliquefaciens</i> FZB42, its mutant AK1S, and their corresponding metabolites showed in vitro inhibition of <i>S. sclerotiorum</i> mycelium. Fengycin derived from an AK1S mutant was purified and identified through HPLC and MALDI-TOF-MS, respectively. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) revealed structural deformities in the fungal mycelium. Moreover, fengycin induced the accumulation of reactive oxygen species (ROS) in <i>S. sclerotiorum</i> mycelium and downregulated the expression of ROS-scavenging genes viz., superoxide dismutase (<i>SsSOD1</i>), peroxidase (<i>SsPO</i>), and catalase (<i>SsCAT1</i>) compared to the untreated control. Furthermore, the lesion size was dramatically reduced in fengycin-treated tomato plants compared to plants infected with <i>S. sclerotiorum</i> only in a greenhouse experiment. Additionally, the transcriptional regulation of defense-related genes <i>GST</i>, <i>SOD</i>, <i>PAL</i>, <i>HMGR</i>, and <i>MPK3</i> showed the highest upsurge in expression at 48 h post-inoculation (hpi). However, their expression was subsequently decreased at 96 hpi in fengycin + <i>S. sclerotiorum</i> treatment compared to the plants treated with fengycin only. Conversely, the expression of <i>PPO</i> increased in a linear manner up to 96 hpi.