Efficient and low-toxicity polymethacrylate guanidine salts for suppressing plant pathogenic fungi in soil: a case study of banana Fusarium wilt

Controlling soil-borne fungal diseases is a major ongoing challenge for modern agriculture. There is a need for new antimicrobial agents that are highly effective, long-lasting, and safe for the environment. Guanidinium-based polymers are promising new candidates. However, it remains technically difficult to tailor their activity against specific pathogens through molecular design. In this study, we designed and synthesized a series of polymethacrylate guanidine salts (PGSs) to meet this need, including both homopolymers and copolymers with diverse side chain architectures. It is found that PGSs show moderately lower broad-spectrum activity than a commercial disinfectant (benzalkonium chloride, BC) against some common microbes (<i>E. coli</i>, <i>S. albus</i>, and <i>C. albicans</i>). However, PGSs were exceptionally effective and selective at inhibiting <i>Fusarium oxysporum</i> f. sp. <i>cubense</i> race 4 (Foc4, the pathogen responsible for banana Fusarium wilt) in soil. A key advantage of PGSs is their strong adsorption to soil, which greatly reduces their spread in the environment and potential toxicity. PGSs showed minimal impact on native soil microbes and aquatic zebrafish. At the same time, this soil binding allows controlled release, sustaining the antifungal effect, and the activity duration of PGSs could reach 30 days, much longer than the 10-day duration of BC. This dual mechanism highlights the potential of PGSs. The successful case against banana Fusarium wilt demonstrates their practical applicability. They could provide an economical, safe, and sustainable solution for persistent soil-borne diseases.