Gene-assisted selection using a pedigree dissection approach to identify Yr genes in wheat breeding materials
Yellow rust is the most dangerous of the wheat rusts worldwide. Disease management involves breeding and fungicide application, with the former being more cost effective and environmentally acceptable. Despite the release of numerous yellow rust resistant cultivars in many countries, new aggressive strains inevitably overcome the resistances in a zigzag or ‘boom and bust’manner. For example, Chamran (Attila-50-Y), released in 1997 in Iran, immediately became the most popular cultivar nationally. In 2012-2013, a new aggressive Pst strain overcame the resistance in Chamran as well as Vee/Nac (an early maturity line suitable for the wheat-maize cropping system) in Khuzestan, a major wheat-producing region in the southwest of the country. Evaluations of wheat germplasm at the Safiabad Agricultural Research Center (North Khuzestan) identified 17 completely or partially resistant lines. Pedigree analyses of resistant lines identified Batavia, Genaro 81, Opata, Pastor, Trap and Yaco as possible sources of resistance. Genotype information of these cultivars obtained from the http://wheatpedigree.net/ database indicated the presence of Yr33, Yr30+Yr18 and Yr31 in Batavia, Opata and Pastor, respectively. Genaro 81, Trap and Yaco carry Yr18. Currently, F2 populations of 34 crosses of 17 resistant lines to locally adapted cultivars Chamran and Vee/Nac are undergoing field selection in a nursery inoculated with the 2012-2013 aggressive race. The progenies of selected plants will undergo further testing and selected homozygous F3 lines will be genotyped for markers associated with Yr18 (Xgwm295-7D), Yr30 (flanking markers Xgwm533.1 - Xgwm493-3B), Yr31 (Xgwm630/Xgwm374-2B (Lr13/Lr23)) and Yr33 (flanking markers Xgwm111 - Xgwm437-7D).