Pathogenicity of root and stolon-colonising fungi to white clover

Fungi isolated from white clover plants growing in dairy pastures in northe rn New South Wales and south-eastern Queensland were tested for their patho genicity to seedlings, excised stolons and mature white clover plants. Thir ty out of 65 isolates tested, including species of Fusarium, Phytophthora, Pythium, Rhizoctonia, Phoma, Codinaea, Gliocladium, Microsphaeropsis, Trich oderma, Nectria and Macrophomina, were pathogenic to white clover roots in vitro. Ten of the fungi, including the genera Alternaria, Colletotrichum, D rechslera, 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 irregular e were the most pathogenic to both seedlings and mature plants. Root rot an d plant growth suppression was more severe in pot tests using field soil co mpared with pasteurised potting mix. Novel methods are described for testin g pathogenicity to excised stolons.