New sources of resistance in Trifolium subterraneum L. to root rot caused by two races of Phytophthora clandestina Taylor, Pascoe and Greenhalgh

Eighty-four genotypes, comprising 71 ssp. subterraneum and ssp. yanninicum breeding lines of Trifolium subterraneum and 13 cultivars commonly used at the time of commencement of the experiment, were screened in the glasshouse for resistance to root rot caused by 2 races of Phytophthora clandestina that occur most widely in Australia. Resistance to race coded 001 was identified in 7 mid-season genotypes of ssp. subterraneum, including the new cultivar, Coolamon, and one genotype also showed resistance to race coded 373. Of the late flowering ssp. subterraneum genotypes tested, 13 showed resistance to race coded 001 and 4 of them also showed resistance to race coded 373. In the late flowering ssp. yanninicum group, 12 of 13 genotypes tested, including the new cultivar, Napier, showed resistance to both races. Of the mid-season ssp. yanninicum genotypes, all but 2 of 19 tested showed resistance to both races. The resistance observed in the majority of ssp. yanninicum and in some ssp. suberraneum genotypes, indicates that these are useful sources of resistance that can be exploited, either directly as new cultivars to minimise damage from this disease, or as parents in breeding programs to develop cultivars with improved resistance to P. clandestina. This study established the availability of 51 advanced lines and 11 cultivars as sources of resistance against P. clandestina race coded 001 and 36 lines and 4 cultivars for race coded 373, among which 36 lines and 4 cultivars were resistant against both races.