Small cationic cysteine-rich defensin-derived antifungal peptide controls white mold in soybean

White mold disease caused by a necrotrophic ascomycete pathogen Sclerotinia sclerotiorum results in serious economic losses of soybean yield in the USA. Lack of effective genetic resistance to this disease in soybean germplasm and increasing pathogen resistance to fungicides makes white mold difficult to manage. Small cysteine-rich antifungal peptides with multi-faceted modes of action hold potential for development as sustainable spray-on bio-fungicides. We have previously reported that GMA4CG_V6 peptide, a 17-amino acid variant of the MtDef4 defensin-derived peptide GMA4CG containing the active {gamma}-core motif, exhibits potent antifungal activity against the gray mold fungal pathogen Botrytis cinerea in vitro and in planta. This peptide exhibited antifungal activity against an aggressive field isolate of S. sclerotiorum 555 in vitro. It markedly reduced white mold disease symptoms when applied to detached soybean leaves, pods, and stems. Spray-application on soybean plants provided robust control of the white mold disease. GMA4CG_V6 at sub-lethal concentrations reduced sclerotia production. It was also non-phytotoxic to soybean plants. Our results demonstrate that GMA4CG_V6 peptide has high potential for development as a bio-fungicide for white mold control in soybean.