Antifungal action of β-pinene derivatives containing quaternary ammonium scaffold against Rhizoctonia solani with damaging cell membranes and affecting energy metabolism

Rhizoctonia solani ( R. solani ) is a phytopathogen that extensively affects crops, leading to plant diseases and reducing crop yields, which jeopardizes food security. β-pinene is a major component of turpentine oil and serves as a lead compound for developing new fungicides. Herein, β-pinene derivatives containing quaternary ammonium scaffold were synthesized in our laboratory, exhibiting broad-spectrum antifungal activity, especially compound bis-hydronopyl dimethyl ammonium bromide ( b-HDAB ). This study aimed to investigate the potential antifungal mechanism of b-HDAB against R. solani . The b-HDAB displayed promising antifungal activities in vitro (EC 50  = 10.20 mg/L and EC 90  = 18.43 mg/L). Its in vivo curative effects (59.82 %) at a dose of 500 mg/L were as remarkable as those of the positive control of validamycin·bacillus (60.58 %). Mechanistically, b-HDAB altered the normal morphology of R. solani mycelium and disrupted its ultrastructure. Meanwhile, b-HDAB increased the relative electrical conductivity of R. solani mycelium, leading to leakage of nucleic acids and proteins from the mycelium. In addition, b-HDAB inhibited the tricarboxylic acid cycle (TCA)-related enzymes, and b-HDAB might exhibit favorable binding stability, potentially through the formation of a pi-cation interaction with the arginine residue (RP357) of pyruvate dehydrogenase (PDH). Metabolomics analysis demonstrated that the content of unsaturated fatty acids of R. solani increased after treatment with b-HDAB , and transcriptomic analysis indicated that b-HDAB destroyed the energy metabolism. These results might guide the development of b-HDAB as an alternative antifungal agent.