Seed Gall Nematodes and Their Association with Toxigenic Bacteria

Annual ryegrass toxicity (ARGT) has caused significant economic damage in Australia. This syndrome occurs when Rathayibacter toxicus is carried by a seed gall nematode into the developing seeds of forage grasses, where it produces a tunicamycin toxin. Grazing animals feeding on infected plants die when they consume sufficient toxin. Consequently, the Animal and Plant Health Inspection Service of the US Department of Agriculture listed R. toxicus as a plant pathogen select agent in the United States. The seed gall nematodes Anguina agrostis, Anguina funesta, Anguina paludicola, and Anguina tritici are regulated or quarantine pests in several countries. A. funesta and A. paludicola are of particular concern because they are the primary vectors of R. toxicus. Several new Rathayibacter species and nematode associations have been described, and we have gained a better understanding of toxin production in R. toxicus and other Rathayibacter species. This review focuses on R. toxicus and other Rathayibacter species; discusses their nematode vectors, distribution, diagnostics, and genomics; and provides suggestions for pathogen risk assessment, surveillance, and management of ARGT.