Identification of Slime Mold Metabolites That Confer Protection to Commercial Crops against Root-Knot Nematodes

Root-knot nematodes are major pests of various crops, coexisting in the soil with amoebae, such as the cellular slime mold Dictyostelium discoideum. Prior studies have indicated that nematodes prey on Dictyostelium, prompting investigations into whether amoebae possess chemical defenses against nematodes for potential use in crop protection. Using improved culture and extraction methods, we found that Dictyostelium releases metabolites acting as repellents against root-knot nematodes, including L-type basic amino acids (e.g., l-histidine, l-arginine) and antioxidants (e.g., l-ascorbic acid, l-cysteine). A mixture of 14 different repellents proved to be extremely potent. The crude conditioned medium that facilitated the identification of these repellents inhibited root-knot nematode egg hatching, exhibited nematocidal effects, and promoted plant growth in pot tests. These findings suggest that the identified compounds and conditioned medium could provide a novel method for nematode control applicable to crops that lack existing control measures.