Qtl Mapping And Molecular Characterization Of Adult-plant Resistance To Stripe Rust In Common Wheat

Stripe rust, caused by Puccinia striiformis f. sp. tritici (PST), is one of the most damaging diseases in common wheat (Triticum aestivum L.) worldwide. Identification of adult-plant resistance (APR) genes to stripe rust in wheat, and characterization of the allelic variation at Yr18/Lr34/Pm38 locus in Chinese wheat landraces, commercial cultivars and CIMMYT advanced lines with functional markers and comparison of their genotypes and maximum disease severities (MDS) are important for durable resistance breeding by pyramiding APR genes. The objectives of this study were to map QTLs of APR to stripe rust in Chinese wheat cultivars Chuanmai 32 and Chuanyu 16, to identify Yr18/Lr34/Pm38 allelic variations in 150 Chinese landraces,47 commercial cultivars and 273 CIMMYT advanced lines using functional markers, and to analyze the genomic sequences of Yr18/Lr34/Pm38 in 4 landraces which had the resistance allele at Yr18/Lr34/Pm38 locus based on molecular marker test, but showed highly susceptible to stripe rust at adult plant stage in the field.The Chinese wheat cultivars Chuanmai 32 and Chuanyu 16 has shown good and stable resistance to stripe rust for 10 years in Sichuan province, a hotspot for stripe rust epidemics. Three populations, with 140 recombinant inbred lines (RILs) each, derived from the crosses of Chuanmai 32/Chuanyu 12, Chuanyu 16/Chuanyu 12 and Chuanmai 32/Chuanyu 16, respectively, were used to map the quantitative trait loci (QTLs) for adult-plant resistance (APR) to stripe rust in the present study. Field trials were conducted in Chengdu and Yaan from 2005 to 2008, providing stripe rust reaction data for six environments. More than 700 simple sequence repeat (SSR) markers were screened for association with stripe rust reaction, initially through bulked segregant analysis (BSA).(1) Two QTLs for stripe rust resistance were detected by composite interval mapping (CIM) in Chuanmai 32/Chuanyu 12 population. They were designated QYr.caas-3BL and QYr.caas-3BS, respectively, and explained from 6.6 to 20.1% of the phenotypic variance across environments. QYr.caas-3BL with major effect came from Chuanmai 32 and QYr.caas-3BS with lower effect was from the susceptible parent Chuanyu 12. Both QTLs appeared to be new.(2) Three QTLs for stripe rust resistance were detected by inclusive composite interval mapping (ICIM) in Chuanyu 16/Chuanyu 12 population. These were designated QYr.caas-1BL.1, QYr.caas-1BL.2 and QYr.caas-2AS, respectively, and explained 4.3-14.7%, 4.6-5.3% and 14.7-38.6% of the phenotypic variance across different environments. One digenic epistatic QTL between QYr.caas-1BL.2 and QYr.caas-2AS explained 4.1-6.0% of the phenotypic variance. QYr.caas-2AS was also detected in Chuanmai 32/Chuanyu 16 population, explaining 23.2-73.0% of phenotypic variance, and it showed the main effect against stripe rust in Chuanyu 16, and located in a similar position to Yrl7, whereas QYr.caas-1BL.1 and QYr.caas-1BL.2 showed minor effects for stripe rust resistance, and QYr.caas-1BL.2 was different from Yr29 although they were at the similar location, and QYr.caas-1BL.1 was likely to be a new QTL for APR to stripe rust on 1BL. The results indicated that APR to stripe rust resistance in Chuanyu 16 was conferred by the three QTLs.(3) A total of 150 Chinese landraces and 47 commercial wheat cultivars were tested using an STS marker csLV34 and 6 functional markers cssfrl-cssfr6 that were developed based on a 3-bp deletion in the exon 11 and a C/T SNP in exon 12 of Yr18/Lr34/Pm38, and they were tested for stripe rust resistance in the field in Chengdu in 2009 and 2010. Of the 150 landraces,119 were characterized to have the resistance allele at Yrl8/Lr34/Pm38 locus, but 37 of them were highly susceptible to stripe rust in the field. Except for these 37 landraces, the average and range of MDS among the three types were Yr18/Lr34/Pm38 resistant genotype< heterozygous genotype< Yr18/Lr34/Pm38 susceptible genotype. The 37 susceptible landraces with Yrl8/Lr34/Pm38 resistance allele were different from Jagger that has a variation in exon 11 and exon 12, using the functional marker cssfr7. Of the 47 commercial wheat cultivars,5 were characterized to have Yr18/Lr34/Pm38 resistance allele. The average and range of MDS of Yr18/Lr34/Pm38 resistance genotype were lower than those of Yr18/Lr34/Pm38 susceptible genotype.(4) STS marker csLV34 and 5 functional markers cssfrl-cssfr5 which were developed based on a 3-bp deletion in the exon 11 of Yrl8/Lr34/Pm38 gene were also employed to test 273 CIMMYT wheat lines. The 273 lines were tested for stripe rust resistance in the field in Chengdu and CIMMYT, leaf rust in CIMMYT, and powdery mildew in Beijing, respectively. Of the 273 lines,43 were characterized to have Yrl8/Lr34/Pm38 resistance allele, with partial resistance against stripe rust, leaf rust and powdery mildew in the field across different environments. The 5 functional markers (cssfrl-cssfr5) could be used to detect the allelic variants at Yr18/Lr34/Pm38 locus, and 43 CEMMYT lines with Yr18/Lr34/Pm38 may be used in wheat breeding targeting for stripe rust, leaf rust and powdery mildew resistance with marker-assisted selection of cssfr3, cssfr4 and cssfr5.(5) Four Chinese wheat landraces, which possessed Yr18/Lr34/Pm38 resistance allele but showed highly susceptible to stripe rust in the field, were used for sequencing analysis of Yr18/Lr34/Pm38 locus. Thirteen pairs of primers were designed for the coding region of Yr18/Lr34/Pm38 locus, and seven pairs of primers were designed for the promoter region of Yr18/Lr34/Pm38. The sequencing results didn't indicate any differences between the coding and promoter region of Yr18/Lr34/Pm38 locus in the 4 landraces and the resistance allele of Yr18/Lr34/Pm38 cloned previously. The susceptibility of the four landraces to stripe rust might be attributed to the presence of inhibitor.