DILOPHOSPORA-ALOPECURI AND DECLINE IN ANNUAL RYEGRASS TOXICITY IN WESTERN-AUSTRALIA

Biological factors contributing to the decline in the incidence of ann ual ryegrass toxicity (ARGT) in Western Australia were investigated. A nnual ryegrass and soil samples were collected in the area where ARGT outbreaks first occurred in Western Australia, an area where the incid ence of ARGT has markedly declined. The nematode vector, Anguina funes ta, was found in 68% of samples, whereas the toxigenic bacterium, Clav ibacter toxicus, was detected in fewer than 2% of samples. The populat ion densities of the nematode were low, but other attributes assayed w ere 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 th e southerly range of A. funesta, but absent in the northerly range whe re 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 contro l ARGT