Phytophthora clandestina, Cause of Severe Taproot Rot of Subterranean Clover in Victoria, Australia. F. C. Greenhalgh, Plant Pathologist, Plant Research Institute, Swan Street, Burnley, Australia, 3121. P. A. Taylor, Plant Pathologist, Irrigation Research Institute, Tatura, Australia, 3616. Plant Dis. 69:1002-1004. Accepted for publication 21 May 1985. Copyright 1985 The American Phytopathological Society. DOI: 10.1094/PD-69-1002.

Surveys showed that the recently discovered fungus Phytophthora clandestina is widely distributed and consistently associated with rotted taproots of subterranean clover in dryland and irrigated pastures of Victoria. Under controlled environmental conditions, P. clandestina caused extensive taproot rot of subterranean clover in pasteurized and untreated sandy loam at either continually high water potentials (0 to –1/3 bar) or alternating high and low (–3 to –5 bar) potentials. The fungus also rotted taproots of plants in pasteurized clay loam and was the probable cause of the disease in untreated clay loam at high water potentials. Fusarium avenaceum and Pythium irregulare did not interact with P. clandestina or cause significant disease in the untreated soils. In addition, the symptoms that these fungi caused on roots in the pasteurized soils were different from those commonly observed in the field. Therefore, the role of F. avenaceum and Pythium irregulare in the etiology of root rots of subterranean clover is questioned.