Advanced backcross quantitative trait locus analysis in winter wheat: Dissection of stripe rust seedling resistance and identification of favorable exotic alleles originated from a primary hexaploid wheat (Triticum turgidum ssp. dicoccoides × Aegilops tauschii)
Stripe rust (Puccinia striiformis W.) causes a range of disease symptoms in hexaploid wheat. We have utilized the AB-QTL (advanced backcross quantitative trait locus) strategy for the genetic dissection of complex disease resistance against stripe rust. An advanced backcross population designated Z86 was made by crossing the winter wheat cultivar Zentos (Triticum aestivum L.) and the primary (exotic) synthetic wheat accession Syn86L (T. turgidum ssp. dicoccoides × Aegilops tauschii). The population Z86, containing 150 BC2F3 lines, was inoculated with the stripe rust isolate R108E141. The disease symptoms were subjected to QTL analysis by using a genetic map based on 118 simple sequence repeat markers. This analysis revealed six QTL effects that were located on chromosomes 1B, 2B, 6B, 7B, 1D and 4D. At four loci, the exotic alleles were associated to increased resistance against stripe rust. The strongest effect, QYrs.Z86-1B, was detected on the short arm of chromosome 1B. Here, the introgression of the exotic allele resulted in 86% enhancement of resistance which explained 37.2% of the genetic variance (R 2). The second favorable effect of an exotic allele was detected on chromosome 1D at QYrs.Z86-1D, which accounted for 72% increase in resistance and explained 18.4% of the R 2. Each of the exotic allele at QTL QYrs.Z86-6B and QYrs.Z86-7B accounted for around 60% enhancement of resistance against stripe rust. At QTL QYrs.Z86-2B and QYrs.Z86-4D, the relative performance of the exotic alleles was inferior due to the pre-eminence of the elite alleles which ranged from 67 to 72%. In addition, QTL analysis revealed four QTL by marker interaction effects. In most cases, the interaction between the elite and exotic alleles brought up resistance in the mixed background of BC2F3 lines. The data presented here provide valuable new genetic resources to be used for stripe rust resistance breeding as well as to isolate new alleles of exotic origin.