Breeding triple rust resistant wheat cultivars for Australia using conventional and marker-assisted selection technologies

Stem rust susceptibility of European wheats under Australian conditions posed a significant threat to wheat production for the early British settlers in Australia. The famous Australian wheat breeder, William Farrer, tackled the problem of stem rust susceptibility through breeding fast-maturing wheat cultivars. South eastern Australia suffered a severe stem rust epidemic in 1973, which gave rise to a national approach to breeding for rust resistance. The National Wheat Rust Control Program was set up in 1975, modelled on the University of Sydney's own rust resistance breeding program, at the University of Sydney Plant Breeding Institute, Castle Hill (now Cobbitty). Back-crossing of a range of sources of resistance provided genetically diverse germplasm for evaluation in various breeding programs. Current efforts are directed to building gene combinations through marker-assisted selection. Major genes for resistance to stem rust and leaf rust are being used in the back-crossing program of the ACRCP to create genetic diversity among Australian germplasm. Stripe rust and to a lesser extent leaf rust resistance in the Australian germplasm is largely based on combinations of adult plant resistance genes and our knowledge of their genomic locations has increased. Additional genes, other than Yr18/ Lr34 and Yr29/ Lr46, appeared to control adult plant resistance to both leaf rust and stripe rust. Two adult-plant stem rust resistance genes have also been identified. The development of selection technologies to achieve genotype-based selection of resistance gene combinations in the absence of bioassays has evolved in the last 5 years. Robust molecular markers are now available for several commercially important rust resistance genes. Marker-assisted selection for rust resistance is performed routinely in many wheat- breeding programs. Modified pedigree and limited back-cross methods have been used for breeding rust- resistant wheat cultivars in the University of Sydney wheat- breeding program. The single back-cross methodology has proved more successful in producing cultivars with combinations of adult plant resistance genes.