Inheritance And Molecular Mapping Of Gene(S) For All-Stage Resistance To Stripe Rust In Several Wheat Cultivars (Lines)

Stripe rust, caused by Puccinia striiformis f. sp. tritici, is a major disease of wheat (Triticum aestivum L.) worldwide. In the US, the disease is most destructive in the western states and has become increasingly important in the south-central states in the past decade. In China, stripe rust is also the most important disease on winter and spring wheat in northwestern, southwestern, huabei and huanghuaihai regions. Estimated losses of 6.0, 3.2, 1.8 and 1.3 million metric tons of wheat occurred in 1950, 1964, 1990 and 2002 nationwide stripe rust epidemics, respectively. Growing resistant cultivars is the most effective approach to control the disease, but only few genes are available conferring effective all-stage resistance against the current populations of the pathogen worldwide. It is urgent to identify new genes for diversifying resistance genes and pyramiding genes for different types of resistance in order to achieve high-level and durable resistance for sustainable control of stripe rust.The common spring wheat genotype PI 181434, originally from Afghanistan, was resistant in germplasm screening nurseries planted in eastern and western Washington from 2004 to 2009. Wheat varieties Libellula and N. Strampelli, which were introduced to China from Italy in 1974, have been widely grown for more than 30 years in the Longnan region of Gansu Province, where stripe rust epidemics are frequent and severe. Although many virulence changes have occurred in the region over the past 35 years, the varieties are still resistant. The wheat-P. huashanica translocation line H9020-1-6-8-3 is also resistant to most of Chinese predominant PST races. The objectives of this study were to identify and map the gene(s) for all-stage resistance in these cultivars (lines) using genetic analysis and molecular markers. The main results gained are as follows:1. PI 181434 was resistant to all tested races of U.S. P. striiformis f. sp. tritici, PST-17, PST-37, PST-43, PST-45, PST-78, PST-100 and PST-127. The genetic study of F2 and F3 derived from AVS/ PI 181434 showed that PI 181434 has a single dominant gene conferring all-stage resistance to PST-100 and PST-127. A linkage map of 8 RGAP markers, Xwgp111, Xwgp112, Xwgp113, Xwgp114, Xwgp115, Xwgp116, Xwgp117, Xwgp118 and 2 SSR markers, Xwmc656 and Xbarc6, was constructed for the gene using the 103 F2 plants. The genetic distance rang from 4.8 to 32.1cM. Amplification of the complete set of nulli-tetrasomic lines and selected ditelosomic lines of Chinese Spring with an RGAP marker and the two SSR markers mapped the gene on chromosome 3DL. Because it is the first gene for stripe rust resistance mapped on 3DL, and different from all previously named Yr genes, the gene in PI 181434 was designated as Yr45. Polymorphism rates of the two closest flanking markers, Xwgp115 and Xwgp118, in 45 wheat genotypes were 73.3% and 82.2%, respectively. Single nucleotide polymorphisms (SNPs) were identified in the eight wheat genotypes sharing both flanking markers. The RGAP markers and potential SNP markers should be useful in incorporating the gene into wheat cultivars and pyramiding with other genes for durable resistance.2. In the seedling tests, Libellula was susceptible to most of prevalent races except resistant to CYR29-mut3 and moderately resistant to moderately susceptible to Su11-4. The resistance to CYR29-mut3 was controlled by one recessive gene. Gene property and allelic analysis showed that the gene is different from known resistance gene Yr3.N. Strampelli was resistant to CYR29, CYR29-mut3, CYR30, CYR31, CYR33, Su11-4, Su11-11, and moderately resistant to moderately susceptible to CYR32. The inheritance results of F1, F2, F3 and BC1 seedling progenies derived from the cross N. Strampelli /Mingxian 169 and N. Strampelli/ Chinese Spring indicated that there are two recessive genes conferring resistance to CYR29 and CYR31, and one confers resistance to CYR29-mut3 and another confers resistance to CYR33, temporarily designated as YrN.S-1 and YrN.S-2. Amplification of Chinese Spring monosomic analysis and SSR markers, the gene YrN.S-1 was located on chromosome 1BL and the gene YrN.S-2 was located on chromosome 5BL. Linkage maps were constructed with three SSR markers, Xgwm499, Xwmc415 and Xwmc537, for the gene YrN.S-1 with genetic distance ranging from 5.4 to 10.7cM and four SSR markers, Xcfa2147, Xgwm124, Xwmc719 and Xwmc44, for the gene YrN.S-2 with genetic distance ranging from 3.2 to 10.3cM. Resistance analysis and molecular tests between the previously named Yr genes located on chromosome 5BL, 1BL and YrN.S-1, YrN.S-2 suggested that both YrN.S-1 and YrN.S-2 are different from these known genes and likely two new stripe rust resistance genes. The markers could be useful in pyramiding these resistance genes with others to develop wheat cultivars with high-level and durable resistance to stripe rust.3. Seedlings tests under controlled greenhouse conditions showed that H9020-1-6-8-3 was resistant to Chinese stripe rust races, CYR25,CYR29,CYR29-mut3,CYR30,CYR31,CYR32,CYR33,Su11-4,Su11-11. Resistance analysis of the parents Psathyrostachys huashanica and common wheat 7182 suggested that the stripe rust resistance gene of H9020-1-6-8-3 was originating from Psathyrostachys huashanica. Genetic studies of F2 and F3 progenies derived from Mingxian169/H9020-1-6-8-3 indicated that a single dominant gene conferring resistance to CYR33, temporarily designated as YrH9020. The mapping population was constructed by 164 F2 individual plants. The linkage map was constructed with three SSR markers, Xgwm261,Xwmc503 and Xgwm102, for the gene YrH9020 with genetic distance rang from 7.0 to 11.2 cM. And the gene was located on chromosome 2DS by three SSR loci. To date, Yr16 was located on chromosome 2DS, which derived from common wheat (Triticum aestivum L.) and is an adult plant resistance gene, so YrH9020 is different from Yr16. The genes from Psathyrostachys huashanica haven't been used widely in wheat resistant breeding. The demonstration of YrH9020 as a new gene and the availability of the flanking SSR markers identified in this study should accelerate its application in breeding programs.