Mapping Of QTLs For Adult-plant Resistance To Stripe Rust And Pyramiding Of QTLs For Adult-plant Resistance To Powdery Mildew In Common Wheat

Stripe rust (caused by Puccinia striiformis f. sp. tritici, Pst) and powdery mildew(caused by Blumeria graminis f. sp. tritici, Bgt), are two of the most destructive foliardiseases of wheat globally. Use of resistant wheat cultivars is the most effective andsustainable approach to control the diseases. Although use of major resistance genes had agreat achievement in controlling stripe rust and powdery mildew, most of them were soonovercome by genetic changes in the pathogen population. Therefore, utilizing the quantitativetrait loci (QTL) or slow-rusting genes can be an important strategy to achieve durableresistance in wheat breeding. The aim of this study was to identify adult-plant resistance(APR) QTL to stripe rust in German cultivar Ibis, and to pyramid APR QTLs to powderymildew in Chinese wheats.1. The German cultivar Ibis has excellent APR to stripe rust in Gansu, a hotspot for striperust in China. To elucidate the genetic basis of APR to stripe rust in Ibis,237F3lines derivedfrom the cross Ibis/Huixianhong were evaluated at Tianshui, Gansu, in the2008-09and2009-10cropping seasons, and at Chengdu in the2009-10cropping season. Inoculations wereconducted with a mixture of several prevalent Pst races CYR32, CYR33and others in theboth locations. The results were summarized below.In the F3population, highly significant correlations (P<0.01) of maximum diseaseseverity (MDS) were found among the three environments, with coefficicients ranging from0.45-0.78, and the broad-sense heritability of MDS was0.75based on the mean valuesaveraged across three environments. A total of723simple sequence repeat (SSR) markerswere used to map the QTL for APR by inclusive composite interval mapping (ICIM). QTLsidentified on chromosomes2BS and6BS, designated as QYr.caas-2BS.1and QYr.caas-6BS.1,respectively. The major effect QTL QYr.caas-2BS.1, flanked by Xgwm148and Xwmc360, wasconsistently detected at all three environments as well as the averaged data over threeenvironments, accounting for40.7,24.2,5.2and29.9%of phenotypic variance, respectively.The other QTL QYr.caas-6BS.1, flanked by Xwmc487and Xgwm768, was detected at twoenvironments (Tianshui2009and Tianshui2010) as well as the averaged data over three environments, accounting for5.8,4.1and4.1%of phenotypic variance, respectively. The twoQTLs accounted for5.2-46.5%of total phenotypic variance across three environments.Significant interaction between the two QTLs was detected in Tianshui2010, explaning13.9%of the phenotypic variance. The results indicated that both additive effects and epistaticeffects on the resistance between QTLs were important genetic component in wheat cultivarIbis.2. Pyramiding QTLs can be an effective approach to develop cultivars with durableresistance to powdery mildew. The wheat cultivars Bainong64and Lumai21possess fourand three QTLs for APR to powdery mildew, respectively. Twenty-one F5lines weredeveloped from the cross Bainong64/Lumai21using a pedigree selection. The lines weregenotyped for powdery mildew using16co-dominant SSR markers closely linked to QTLs onchromosomes1A,4DL,7A,6BS,2DL,2BS and2BL and they were planted in randomizedcomplete blocks with two replicates in Beijing during2009-10and2010-11cropping seasons,and evaluated for powdery mildew response using the highly virulent Blumeria graminis f. sp.tritici isolate E20. The results were as follows: The genotypic analysis indicated that17linescombined QTLs donated by both parents, five lines carried five QTLs,15lines possessedthree or four QTLs, one line had two QTLs, and ten lines possessed common QTLs onchromosome1A,4DL and7A derived from the parent Bainong64. Twelve lines had lowerMDS and area under the disease progress curve(AUDPC) than both parents. The pyramidedlines and parents were categorized into11genotypes, of which six genotypes pyramidingQTL combinations QPm.caas-1A and QPm.caas-4DL in common along with one or more ofthe others expressed higher APR to powdery mildew than the more resistant parent Bainong64. Thus, pyramiding these two QTLs and one or more of QPm.caas-2BS, QPm.caas-2BL,and QPm.caas-2DL from Lumai21could be a desirable strategy to breed cultivars with ahigh level of durable resistance to powdery mildew.Molecular markers identified in Ibis could be used in marker-assisted selection toimprove APR to stripe rust in wheat breeding. The pyramided lines with multiple QTLs andhigh APR to powdery mildew were developed from the cross Bainong64/Lumai21, whichprovide breeders an effective approach for developing durable resistance to powdery mildewor stripe rust by pyramiding QTLs in wheat.