ABSTRACT
Gaeumannomyces graminis is a homothallic, ascomycete fungus which exists in three varieties: G. graminisvar. tritici (Ggt), G. graminis var. avenae (Gga), and G. graminis var. graminis (Ggg). Ggt is the cause of take-all disease of wheat and barley. Gga is the cause of take-all disease of oats and take-all patch disease of turf grasses; it also infects wheat and barley. Ggg is the cause of crown (black, brown) sheath rot of rice; it is usually not pathogenic for wheat or barley. All three varieties have a wide grass host range. Take-all disease of wheat and barley is essentially a root rot disease. Isometric virus particles were first discovered in a field isolate of Ggt in France. Since then, similar particles have been found in isolates of Ggt, Gga, Phialophora sp., and P. graminicola from many other parts of the world.
