Fine Mapping TaFLW1,a Major Gene Controlling Flag Leaf Width In Bread Wheat

Given the importance of wheat as a staple food,improvement of yield potential is one of the major goals of wheat breeding programs.As a principle organ in wheat,leaf is involved in many fundamental physiological functions such as photosynthesis and transpiration.The flag leaf,which is the last leaf to emerge before the spike,is generally regarded as the major source of the carbohydrates stored in grains.The morphological traits of flag leaf such as size and shape have been considered to be the important determinants of grain yield potential in wheat.In our previous study,a major quantitative trait loci?QTL?Qflw.nau-5A,controlling wheat flag leaf width?FLW?was detected on chromosome 5A by using a recombinant inbred line?RIL?population derived from Nanda 2419 × Wangshuibai.This QTL was precisely mapped to a 0.2 cM Xwmc492-Xwmc752 interval by screening and analysing the recombinants,and was named as TaFLW1.To fine map TaFLW1,we constructed near isogenic lines?NIL?of this gene by using two varieties Mianyang 99-323 and PH691 as the recurrent parents.FLW inheritance was investigated using two F₂ populations developed from crossing the NILs with their recurrent parents.In order to further reduce TaFLW1 interval,we developed 144 new markers,including SSR,STS and CAPS/dCAPS markers.The marker we designed based on the TaFLWl interval collinearity with Brashypodium and rice,SNP chip data and wheat D genome sequence information.Finally,a high,resolution map of TaFLWl interval was constructed by genotyping the two secondary F₂ populations with all markers mapped in the interval.237 and 278 recombinants were identified from 5537 F₂ plants with Mianyang 99-323 background and 6211 F₂ plants with PH691 background.The 48 key homozygous recombinants in Xwmc492-Xwgrb101 interval were measured in 2013-2015 in multiple field trials.These key recombinants in the TaFLW1 interval c ould be clearly classified into two groups based on their FLW trait.Compared the genotype and phenotype data of the identified recombinants,the TaFLW1 was finally delimited to the 0.040-0.063 cM interval in Xwmc492-Xwgrb101 region,and co-segregated with the primer Xwgrb390,Xwgrb 125 and Xwgrb 417.The primer WGRB125 was used to analysis the allelic variations in mini-core germplasm,which includes 267 materials.The four environments correlation coefficients result shows that WGRB125 were significantly associated with the flag leaf width trait.Haplotype analysis indicated that Hap2-186 bp,Hap3-188 bp and Hap4-190 bp was the predominant haplotypes,account for 92.1%of the total population in all six types.In the 111 breeding varieties,68.5%of the material carried the Hap2 or Hap4 with wide flag leaf trait,showing that breeders has a certain choice with wide flag leaf trait in the breeding process.