QTL Mapping Of Slow Stripe Rust Resistance And Analysis Of Slow Mildewing Genes For Resistance To Stirpe Rust And Leaf Rust In Common Wheat

Stripe rust, leaf rust and powdery mildew are the devastating diseases in common wheat (Triticumaestivum L.) worldwide. Use of resistant wheat cultivars is the most economic, effective andenvironmentally friendly approach to reduce the losses caused by the diseases. Although utilization ofmajor resistance genes has gained a great achievement in increasing the wheat resistance during the pastdecades, most of them were soon overcome by new isolates due to genetic changes in the pathogenpopulation, resulting in devastating yield losses. Identification of new slow rusting and slow mildewingresistance genes and pyramiding multi-resistance QTL by marker-assisted selection are of greatimportance to develop new cultivars with durable resistance to multiple diseases.The aim of this study was to identify slow stripe rusting QTL in Linmai2/Zhong892RILpopulation, and analyze the slow mildewing genes for resistance to stripe rust and leaf rust in commonwheat by gene pyramiding. The main results are summarized as follows:1.The273RILs derived from the Linmai2/Zhong892cross and their parents were evaluated atPianxian, Sichuan province, in the2011-12,2012-13and2013-14cropping seasons, and at Qingshui,Gansu province, in the2012-13cropping season. The RILs and their parents were genotyped withWheat90k SNP iSelect assay. In the RIL population, highly significant correlations (P<0.0001) ofmaximum disease severity (MDS) were found among the four environments, with correlationcoefficients ranging from0.65-0.81, and the broad-sense heritability of MDS was0.59. A genetic mapwith a total length of16465.6cM was constructed by7083single nucleotide polymorphism (SNP)markers using IciMapping v3.2. QTL mapping was performed by Inclusive composite interval mapping(ICIM). Two QTL, designated QYr.caas-3B.1and QYr.caas-3B.2on chromosome3B, conferred stableresistance to stripe rust across multi-environments, explaining8.2-11.3%and6.2-12.2%of phenotypicvariance, respectively. Six QTL, designated QYr.caas-1BL.2, QYr.caas-2BL.3, QYr.caas-2DL.2,QYr.caas-3AS, QYr.caas-4BS and QYr.caas-7BS located on the chromosomes1BL,2BL,2DL,3AS,4BS and7BS, were detected on single environments, explaining18.2%,4.9%,5.1%,6.9%,15.2%and10.5%of phenotypic variance, respectively. The resistance alleles of QYr.caas-1BL.2, QYr.caas-3B.1,QYr.caas-3B.2, QYr.caas-4BS and QYr.caas-7BS were contributed by Zhong892, whereas those ofQYr.caas-2BL.3, QYr.caas-2DL.2and QYr.caas-3AS were from Linmai2. These QTL can reduce theMDS of stripe rust effectively and is potentially useful in wheat breeding.2. Pyramiding quantitative trait loci (QTL) for resistance to powdery mildew, stripe rust and leafrust can be an effective approach to wheat cultivars with multiple and durable resistance. In the presentstudy,21F6lines combining two to five slow mildewing QTL were developed from the cross ofBainong64/Lumai21. Wheat cultivars Bainong64and Lumai21with good agronomic traits conferredslow mildewing resistance, possessing four and three slow mildewing QTL, respectively. The21F6lines were grown in Pianxian and Qingshui for stripe rust test, and in Baoding and Zhoukou for leaf rusttest during2012-13cropping season. Both the MDS and the area under the disease progress curve(AUDPC) were analyzed to evaluate the resistance to stripe rust and leaf rust of individual slow mildewing QTL and QTL combinations. Analysis of variance indicated highly significant effects ofslow mildewing QTL QPm.caas-2BL, QPm.caas-4DL and QPm.caas-6BS on stripe rust, contributing17.3%,16.9%and14.1%of phenotypic variance, respectively. QPm.caas-4DL also showed highlysignificant resistance to leaf rust and contributed35.3%of phenotypic variance. QTL combinationsQPm.caas-1A/QPm.caas-4DL/QPm.caas-2DL/QPm.caas-2BS/QPm.caas-2BL and QPm.caas-1A/QPm.caas-4DL/QPm.caas-2BS/QPm.caas-2BL exhibited highly significant resistance to stripe rust andleaf rust. Both of the two pyramided QTL combinations possessed QPm.caas-4DL come from Bainong64, and QPm.caas-2BS and QPm.caas-2BL from Lumai21. This indicated that QPm.caas-2BS andQPm.caas-2BL have significant effects of resistance to these diseases. Thus pyramiding QPm.caas-4DLfrom Bainong64with QPm.caas-2BS and QPm.caas-2BL from Lumai21could be a good strategy tobreed cultivars with a high level of durable resistance to the three kinds of wheat diseases. In addition,lines possessing higher numbers of QTL showed more resistant to the diseases, and a high level ofresistance can be achieved by pyramiding4-5slow mildewing or rusting QTL. These results are usefulfor pyramiding slow mildewing or slow rusting QTL in wheat to develop cultivars with durableresistance to multiple diseases.