Dilophospora alopecuri and decline in annual ryegrass toxicity in western Australia.
Biological factors contributing to the decline in the incidence of annual ryegrass (Lolium rigidum) toxicity (ARGT) in Western Australia were investigated. Annual ryegrass and soil samples were collected in the area where ARGT outbreaks first occurred in Western Australia, an area where the incidence of ARGT has markedly declined. The nematode vector, Anguina funesta, was found in 68% of samples, whereas the toxigenic bacterium, Clavibacter toxicus, was detected in <2% of samples. The population densities of the nematode were low, but other attributed assayed were normal. The fungus, Dilophospora alopecuri, also associated with A. funesta, was found at 58% of the sampling sites. The abundance of D. alopecuri suggests that it is an important contributor to decline in ARGT. Therefore, the distribution of D. alopecuri in Western Australia was determined in the following season. D. alopecuri was common in the southerly range of A. funesta, but absent in the northerly range where ARGT outbreaks are still common. In the south, D. alopecuri appears to have displaced C. toxicus and reduced A. funesta populations. The findings suggest that there is potential to use D. alopecuri to control ARGT.