Construction Of An Integrated Genetic Map And QTL Detection For Early-maturing Traits In Short-season Cotton (G. Hirsutum L.)

Cotton is one of the important economic crops, also the important raw materials in textileindustry, and plays an important role in the world and in national economy in China.Short-season cotton, which is also called early-maturing cotton, is a special kind of cottonecological types. The selection and popularization of short-season cotton has significant valuein alleviating the contradiction for land between cotton and cereals, and in optimizingagricultural structure. It is an effective way that making use of the molecular markers methodwhich linked to QTL for goal traits, to dig and analyze QTL for early maturity traits. In ourresearch, the short-season cotton cultivar Baimian2was used as the central parent to generatetwo F2and F2:3family lines from the two crosses, Baimian2×TM-1and Baimian2×CIR12.A genetic integrated map was constructed based on SSR molecular method, which containedthe most markers and covered the highest area of the map in short season cotton; moreover,some QTL for early-maturing traits in cotton were located by CIM. The results were showedas follows:1. The genetic map in short-season cottonTaking advantage of the F2populations constructed two genetic maps by two crosses andthen integrated the two individual maps together. The map from Cross I harbored269locispread to43linkage groups that spanned1837.8cM (approximately36.76%of the cottongenome) with an average distance of6.883cM between two markers, two linkage groups can'tapply to the corresponding chromosome. The length range was between3.0cM and119.4cM,and the number of markers was between2and5; Chr.24was the longest linkage group141.8cM and contained marker loci29.The map from Cross II harbored127loci spread to33linkage groups that spanned 1244.3cM (approximately24.89%of the cotton genome) with an average distance of9.797cM between two markers, five linkage groups can't apply to the correspondingchromosome. The length range was between4.5cM and92.5cM, and the number of markerswas between2and10; Chr.9was the longest linkage group168.4cM and contained markerloci11.The integrated map contained325loci spread to33linkage groups that spanned2535.6cM (approximately50.71%of the cotton genome) with an average distance of7.592cM between two markers. Chromosomes1,9,17, and24had more than20loci and thetotal length was between152.0cM and229.5cM. Chromosome24had the most loci (32) andchromosome9had the longest length (229.5cM).2. QTL detection for early-maturity traitsThe F2:3population of the two combinations were used to detected QTL forearly-maturing traits on seedling period (SP), bud period (BP), flower and boll period (FBP),growth period (GP), yield percentage before frost (YPBF), first fruiting branch node (FFBN),and height of first fruiting branch node (HFFBN). In Com I, the number of located QTL was53, twenty-two significant QTL which had LOD scores greater than3.0or greater than thethreshold calculated by permutation test were detected. The rest thirty-one were suggestiveQTL. These QTL were located to Chr.1(A1), Chr.6(A6), Chr.9(A9), Chr.10(A10),Chr.11(A11), Chr.13(A13), Chr.16(D7), Chr.17(D3), Chr.20(D10), Chr.22(D4), Chr.24(D8),Chr.25(D6), Chr.11/Chr.21(A11/D11), Chr.12/Chr.26(A12/D12), LG2. By analyzing thehereditary,24QTL represented additive effects and29represented dominant or overdominant effects; the favorable gene for37QTL were derived from Baimian2and16werederived from TM-1. In Cross II, the number of located QTL was33, including fourteensignificant QTL and nineteen suggestive QTL. These QTL were located to Chr.3(A1),Chr.5(A5, Chr.7(A7), Chr.8(A8), Chr.9(A9), Chr.11(A11), Chr.12(A12), Chr.17(D3), Chr.14(D2), Chr.8/Chr.24(A8/D8), Chr.12/Chr.26(A12/D12), LG3, LG5, LG6; by analyzing,14QTL represented additive effects and19represented dominant or over dominant effects;the favorable gene for21QTL were derived from Baimian2and12were derived from CIR12.Among ten early-maturing traits, one to ten QTL were detected in every trait; and there'sat least one dominant QTL were detected except growth period in cross II. In the present study,the genetic effects of early-maturing traits analyzed by molecular approach suggesting thatearly-maturing traits may be controlled mainly by dominant or over dominant effects. And thefavorable gene for early-maturing traits was derived from Baimian2.Furthermore, there were seven common QTL in the two crosses except bud period,flower and boll period, and node of the forts fruiting branch. Of these QTL, qBP-17for budperiod, qGP-17a/qGP-17b (qGP-17) for growth period, qPSB-17for pre-summer boll,qSB-17a/qSB-17b(qSB-17)for summer boll, qAB-17q for autumn boll,YPBF-17a/qYPBF-17b (qYPBF-17) for yield percentage before frost, qHFFBN-17for heightof first fruiting branch node were always detected close to the common markers DPL0041onChr.17in the two crosses. The favorable genes for these QTL were all derived from the sameparent Baimian2, so they should be common QTL.