| Global wheat production is being threatened by several fungal diseases, including stripe rust and leaf rust. In this study, a mapping population of 96 recombinant inbred lines generated from the cross of Jagger x 2174, two bread wheat cultivars (Triticum aestivum, 2n=6x=42, AABBDD) was tested at three sites, in Washington where predominant races PST-114 and PST-116 naturally occurred, in Kansas where PST-100 was inoculated, in Beijing, China where a predominant stripe rust race CYR32 was inoculated on adult plants. A major quantitative trait locus (QYr.osu-2A) for adult-plant stripe rust resistance was located on the short arm of chromosome 2A, where Jagger was found to carry markers for resistance gene Yr17 from Triticum ventricosum. Thus Yr17 was likely responsible for the phenotypic variation at QYr.osu-2A. In addition, a novel QTL for consistent resistance to multiple races of the stripe rust pathogen was mapped on the long arm of chromosome 5A ( QYr.osu-5A), where Jagger had the resistant allele whereas 2174 had the susceptible allele. A significant genetic effect of the resistance gene Lr34/Yr18 in 2174 was detected only when the population was tested with CYR32 in China. The resistant allele at QYr.osu-2A was found to occur frequently in cultivars from the southern Great Plains but occasionally in cultivars from other U.S. wheat regions. Lr34 is one of the most important disease-resistance genes in wheat worldwide, because of the durability and race non-specificity of its resistance against multiple pathogens including leaf rust and stripe rust. In this study, we found that among completely sequenced 23 cDNA clones from a cultivar carrying the resistant Lr34 allele, only a portion (35%) of its transcripts were correctly spliced, and the remainder of Lr34 transcripts was incorrectly spliced due to different intron retention or exon skipping events. The most frequently occurring mis-splicing events were 92 bp skipping at the 5' end of exon 10 and 44 bp skipping at the 5' end of exon 12. All mis-splicing events observed in this study resulted in non-function to leaf rust resistance, except for one that retained 12 bp at the 3' end of intron 6 and thus attained an additional four amino acids. These findings suggested that the partial resistance conferred by L34 might be due to the mis-splicing events and that the level of resistance from a partial resistance gene could be increased to a significantly higher level by eliminating or mutating regulators which cause mis-splicing events. |
