INTROGRESSION OF QUANTITATIVE TRAIT LOCI (QTLS) DETERMINING STRIPE RUST RESISTANCE IN BARLEY - AN EXAMPLE OF MARKER-ASSISTED LINE DEVELOPMENT

Genome-analysis tools are useful for dissecting complex phenotypes and manipulating determinants of these phenotypes in breeding programs. Q uantitative trait locus (QTL)-analysis tools were used to map QTLs con ferring adult plant resistance to stripe rust (caused by Puccinia stri iformis f.sp. hordei) in barley. The resistance QTLs were introgressed into a genetic background unrelated to the mapping population with on e cycle of marker-assisted backcrossing. Doubled-haploid lines were de rived from selected backcross lines, phenotyped for stripe-rust resist ance, and genotyped with an array of molecular markers. The resistance QTLs that were introgressed were significant determinants of resistan ce in the new genetic background. Additional resistance QTLs were also detected. The susceptible parent contributed resistance alleles at tw o of these new QTLs. We hypothesize that favorable alleles were fixed at these new QTLs in the original mapping population. Genetic backgrou nd may, therefore, have an important role in QTL-transfer experiments. A breeding system is described that integrates single-copy and multip lex markers with confirmation of the target phenotype in doubled-haplo id lines phenotyped in field tests. This approach may be useful for si multaneously producing agronomically useful germplasm and contributing to an understanding of quantitatively inherited traits.