Disease-Suppressive Activity of Lecithin Against Foliar Infection by Rhizoctonia solani Isolates in Cabbage, Rice, and Brachypodium distachyon

Rhizoctonia solani is a necrotrophic phytopathogenic fungus that causes disease in various crops. In agriculture, many crops suffer from root or seedling rot caused by this soil-borne pathogen, whereas cabbage and rice develop lesion-like symptoms on aboveground tissues. Diseases caused by R. solani are generally controlled using chemical fungicides; however, environmentally friendly alternatives are needed for sustainable agriculture. In this study, we evaluated the efficacy of lecithin, a mixture of phospholipids previously registered in Japan as an agrochemical for controlling cucumber powdery mildew, against Rhizoctonia diseases. In cabbage, foliar spraying of 0.2–1.0% soybean lecithin effectively suppressed leaf symptoms caused by R. solani isolate RhiCa-2, which was identified as AG-1 IB. In rice and Brachypodium distachyon, 0.2–1.0% lecithin significantly suppressed leaf symptoms induced by R. solani AG-1 IA. Hyphal staining of inoculated leaves revealed reduced hyphal density on lecithin-treated leaves. Consistently, hyphal growth of R. solani on cellophane placed on water agar was retarded by lecithin treatment. However, 5.0% lecithin induced phytotoxicity in B. distachyon. Egg yolk-derived lecithin also exhibited disease-suppressive activity in cabbage and B. distachyon, with efficacy comparable to that of soybean lecithin under the conditions tested. These results suggest that lecithin suppresses foliar infection by R. solani, at least in part, through direct inhibitory effects on fungal hyphae, and may serve as a potential alternative material for disease control in sustainable crop production.