Annual ryegrass toxicity (Rathayibacter toxicus) is a bacterial pathogen of Ryegrass. It is a native of Australia.
R. toxicus in soil adheres to the surface of the Anguina nematode and is carried into the plant when the nematode feeds. Bacteria grow in the seed heads, and in galls formed by the nematode, where they proliferate as yellow bacterial slime. Bacteria reenter the soil when infected seeds fall. Toxins are produced by R. toxicus as the grass matures. When infected grasses are consumed, animals suffer neurological symptoms, toxicosis and death.