Resistance to race 2 and cross-resistance to race 1 of Kabatiella caulivora in Trifolium subterraneum and T. purpureum

Twelve cultivars and 10 F-6-derived breeding lines of subterranean clover (Trifolium subterraneum) and two cultivars of purple clover (T. purpureum) were screened in the field for their response to clover scorch disease caused by race 2 of Kabatiella caulivora that is restricted in distribution in Western Australia but is generally more virulent than race 1. Two of the cultivars (viz. Coolamon subterranean clover and Electra purple clover), and the breeding line SL031 showed outstanding resistance, with disease scores significantly lower than the resistant cultivar Denmark that had a disease score of 3.3 (0-10 scale with 0 = no disease and 10 = death of all plants). A further two cultivars (viz. Goulburn, and Karridale) and four of the breeding lines (viz. SL019, SL027, SL029 and SM033) had similar levels of resistance to Denmark. Host responses to race 2 were compared with those against race 1 of K. caulivora. Genotypes, such as SL029 and SL031, with combined resistances to both races of K. caulivora were identified, and their potential for effective management of K. caulivora, in areas where both races occur, highlighted.