Genetic diversity for rust resistance among Nordic spring wheat cultivars

Wild relatives, landraces and cultivars from different geographical regions are demonstrated sources of resistance to wheat rusts. Identification, characterisation and provision of diverse sources of rust resistance to Australian wheat breeding companies form a key component of the Australian Cereal Rust Control Program. This study was planned to assess diversity of resistance to the three rusts among a set of Nordic spring wheat cultivars. These cultivars were tested at the seedling stage with several pathotypes of each rust pathogen. Stem rust resistance genes Sr7b, Sr8a, Sr12, Sr15, Sr17, Sr23 and Sr30 and leaf rust resistance genes Lr1, Lr3a, Lr13, Lr14a, Lr16 and Lr20 were postulated either singly or in various combinations. A high proportion of cultivars were identified to carry Sr15/Lr20 presumably due to earlier selection, or fixation, of Pm1 in breeding populations. Seedling test data using five Pst pathotypes did not allow postulation of genes present in a many cultivars because of a widely effective single gene or overlapping effectiveness of two or more resistance genes. Stripe rust resistance gene Yr27 was postulated in five cultivars. The presence of Yr1 in one cultivar was predicted by amplification of the linked marker allele. Eighteen, 47 and 32 cultivars showing seedling susceptibility, respectively, to stem rust, leaf rust and stripe rust were tested under field conditions to identify sources of adult plant resistance (APR). Cultivars possessing APR to all three or to two rusts were identified. Molecular markers linked to APR genes Lr34/Yr18/Sr57, Lr68, and Sr2 detected the likely presence of these genes in some cultivars.