Anti-Rhizoctonia solani activity by polymeric quaternary ammonium salt and its mechanism of action

Abstract

Polymeric quaternary ammonium salts (PQASs) exhibit antibacterial action and are less toxic, less stimulatory to the human body and have easier-to-modify functionalities than small molecular antibacterial agents. However, few studies on the structure-activity relationship and toxicity mechanism of PQASs against fungi have been reported. We previously described the synthesis of a novel PQAS, namely, a homopolymer of (2-methacrylamido)propyltetrabenzyldimethylammonium chloride (PQD-BC), and discovered that the polymer exhibits antifungal activities not only against Fusarium oxysporum f. sp. Cubense tropical race 4 (Foc 4), the pathogen of banana wilt, but also against Rhizoctonia solani (R. solani), the pathogen of rice sheath blight (RShB). Furthermore, we studied the mechanism of action of PQD-BC against Foc 4, which is markedly different from R. solani in morphology and life cycle. Therefore, the structure-antifungal activity relationship and toxicity mechanism of PQD-BC against R. solani were extensively studied in this work and compared with those of the low-molecular-weight quaternary ammonium salt benzyldimethyldodecylammonium chloride (BC), and the results play an important role in identifying long-term and low-toxicity fungicides that can suppress the sclerotia of R. solani. The results showed that PQD-BC and BC can destroy the structural integrity and morphology of a cell, such as by loss of the cell wall and plasma membrane integrity, leading to the release of intracellular contents and can induce mitochondrial dysfunction and interference with genomic DNA and inhibit the formation of sclerotia. However, PQD-BC showed a special mechanism for causing the lipid peroxidation of the cell membrane; this mechanism was not observed with BC. The newly elucidated mechanism accounts for differences between polymers and small-molecule compounds and provides a theoretical basis for further application of PQAS against fungi and sclerotia.