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Quantitative Assay of Pachymetra chaunorhiza, a Root Pathogen of Sugarcane in Australia. R. C. Magarey, Research plant pathologist, Bureau of Sugar Experiment Stations, P.O. Box 566, Tully, Queensland, Australia 4854; Phytopathology 79:1302-1305. Accepted for publication 23 June 1989. Copyright 1989 The American Phytopathological Society. DOI: 10.1094/Phyto-79-1302.

A quantitative assay based on the direct count of oospores extracted from soil was developed for Pachymetra chaunorhiza, a recently described pathogen associated with poor root syndrome of sugarcane in Australia. The efficiency of oospore recovery and the size distribution of oospores in a naturally infested soil were investigated. The relationship between soil oospore density and P. chaunorhiza root rot was investigated with a susceptible sugarcane cultivar Q90 growing in pasteurized soil inoculated with cultured oospores, in naturally infested field soils diluted with pasteurized soil, and in assayed soils infected with P. chaunorhiza. The results suggest a strong relationship between oospore population and root rot and indicate that the assay is a useful method for quantifying P. chaunorhiza in field soils.