MICROBIOLOGICAL ASPECTS OF SUGARCANE YIELD DECLINE

Sugarcane is an important Australian crop earning over $1.8 billion in export revenue annually. The crop is grown as a monoculture, and much of the production area has been continually cropped for over 60 years . Increasing production trends plateaued in the 1970s and soil based c onstraints now reduce industry income by $200m annually. The condition , termed sugarcane yield decline (YD), is similar to replant diseases in other crops. Large growth responses to soil fumigation, soil solari sation. and the application of fungicides, suggest that soil microbiol ogy is intimately involved. Research has identified a previously uncla ssified oomycete, Pachymetra chaunorhiza, as a new sugarcane root path ogen. Additional root pathogens identified include Pythium arrhenomane s and various nematode species. Other organisms which appear to be inv olved in YD, are discussed.