Pathogenicity of root and stolon-colonising fungi to white clover

Fungi isolated from white clover plants growing in dairy pastures in northern New South Wales and south-eastern Queensland were tested for their pathogenicity to seedlings, excised stolons and mature white clover plants. Thirty out of 65 isolates tested, including species of Fusarium, Phytophthora, Pythium, Rhizoctonia, Phoma, Codinaea, Gliocladium, Microsphaeropsis, Trichoderma, Nectria and Macrophomina, were pathogenic to white clover roots in vitro. Ten of the fungi, including the genera Alternaria, Colletotrichum, Drechslera, Fusarium, Phoma, Macrophomina, Phomopsis and Rhizoctonia, caused stolon rot symptoms. Of the 23 fungi tested on seedlings and mature white clover plants Phytophthora megasperma, Phoma nebulosa and Pythium irregulare were the most pathogenic to both seedlings and mature plants. Root rot and plant growth suppression was more severe in pot tests using field soil compared with pasteurised potting mix. Novel methods are described for testing pathogenicity to excised stolons.