Root rot of subterranean clover in the irrigation areas of south-western Western Australia

Abstract

Investigations in 1974 identified the fungi associated with the roots of subterranean clover at four irrigated sites at Wagerup, Western Australia. Two of these sites had previously had a disease problem, two were apparently healthy. A range of fungi were isolated, including Pythium irregulare, P. debaryanum, P. acanthicum, P. middletonii, Fusarium oxysporum, and Rhizoctonia spp. There was a more rapid buildup of Pythium spp. population following the initial irrigation, and an overall lower incidence of Fusarium spp., at the diseased sites. The incidence of Rhizoctonia spp. was usually low and variable at all sites. Disease index ratings rose more rapidly for diseased sites. No association was proven between disease incidence and soil water potential. The three most frequently isolated fungi; viz. P. irregulare, P. acanthicum, and F. oxysporum, were all shown to be capable, under the conditions of this investigation, of producing high levels of tap and lateral root rot, and of causing reductions in seedling emergence. In some cases the levels of both tap and lateral root rot were increased, and the plant emergence decreased, by the application of two or more fungi in combination in comparison with application of a single fungus. Overall P. irregulare was the most pathogenic of the fungi tested.