New sources of resistance in Trifolium subterraneum to rust (Uromyces trifolii-repentis)

Fifty-seven genotypes, including 10 cultivars, of Trifolium subterraneum var. subterraneum and var. yanninicum were screened in the field for resistance to rust (Uromyces trifolii-repentis) using artificial inoculation. There was outstanding resistance among the var. yanninicum, types with all but 1 genotype showing no rust symptoms. Several var. subterraneum genotypes also showed only a low rust incidence (<= 3.5 on a 0-10 scale) with little or no leaf collapse from rust infection, including 83S19-07, CPI 103906F, EP132Sub-E, 84S20-02, and 84S20-01. Several other lines had a significant incidence of rust, while little leaf collapse from the disease was evident. Several highly susceptible lines were identified, including cultivars Green Range, Seaton Park and York, all with 100% of leaves affected by rust and extensive leaf collapse. There was excellent positive correlation between rust incidence and leaf collapse across the genotypes tested (R-2 = 0.91). The excellent rust resistance observed in the majority of var. yanninicum lines and the good resistance in some var. subterraneum lines, indicates that these are useful sources of resistance that can be exploited, either directly as new cultivars to minimise leaf collapse from this disease or as parents in breeding programmes to develop more rust-resistant cultivars.