QTL Mapping Of Yield And Fiber Quality Traits In Gossypium Hirsutum L. And Recurrent Selection With MAS

Cotton is the most important textile fiber crop and the world's second-most important oil-seed crop after soybean.Since the 90's of last century,the breeding of Upland cotton (Gossypium hirsutum L.) cultivars had step into a new period characterized with ultility of heterosis in China.The developments on molecular marker technology offer plant breeders a powerful tool to understand genetic basis of heterosis and make use of it in breeding. Especially,if the marker tightly linked with major gene controlling interesting traits was identified,selection assisted with the marker will improve the efficiency of selection for improving cultivars for yield,products quality,pest resistance,etc.No genetic linkage map derived from upland cotton cultivars and coverd most cotton genome was reported because of their narrow genetic basis and low genetic polymorphism. Only a fraction of the cotton genome was exploited when these crosses derived from upland cotton cultivars were used to QTL mapping,and the results of QTL mapping was not valuable for MAS.Classic selection methods were low power for cotton breedingIn this paper,molecular markers and segregated populations derived from more paprents than two were used to develop genetic linkage map and to exploit QTLs concerned with yield and fiber quality.These parents were also parents of four hybrids,Xiangzamian2, Wanza40,Zhongza028 and Nankang3 which were popularized hybrids in the Changjiang River valley and in the Huanghe River valley.For the popurse of pyramiding more super genes,specific combining ability reciprocal recurrent selection method was used to break down linkage-drag among yield components,and high yield and low fiber quality between two initial populations derived from the same parents was used for QTL mapping populations.MAS was conducted with QTL mapping results to accelerate the procedure of populations improvement,and pick out materials pyramided more super genes for the hybrid breeding during the specific combining ability reciprocal recurrent selection procedure.The results are followed:1.A four-way cross segregated population,Simian3/Sumian12//Zhong4133/8891,and its F_2:3 inbreed lines were constructed.The four materials Simian3,Sumian12,Zhong4133 and 8891,which originated from Changjiang River valley,were the parents of the elit hybrids Xiangzamian2,Wanza40,Zhongza028 and Nankang3.A linkage map was developed for the four-way cross with SSR markers and JOINMAP3.0 software.The map is comprised of 55 linkage groups with 286 mapped loci which span between 0.37cM and 125cM.The 286 loci covered 2113.3cM,which was approximately 42%of the total recombination length of the cotton genome.The average distance between loci was 7.4cM genome wide.Twenty four linkage groups were assigned to A-subgenome,contain 126 loci and span 808.4cM and 27 linkage groups were assigned to D-subgenome,contain 152 loci and span 1231.6cM.The average distance between loci was 6.4cM in A-subgenome and 8.1cM in D-subgenome.Five remained linkage groups were failed to be assigned to any chromosomeIn the four-way cross population,QTLs concerned with plant architecture and physiology traits included plant height,plant branches,leaf chlorophyll content, photosynthetic rates and date of first square,and yield and yield components traits involved number of bolls per plant,boll weight,lint percent,number of seeds per boll,seed index, lint index,seed cotton yield per plant and lint yield per plant,and fiber quality traits,such as fiber length,fiber strength,micronaire reading,fiber elongation ratio and fiber uniformity were detected with MAPQTL5.0.Fourteen suggestive QTLs and two significant QTLs controlled plant architecture and physiology traits were detected with explained 4.0% to 19.4%of the phenotypic variation.Twenty six suggestive QTLs and five significant QTLs concerned with yield and yield components traits were detected with explained 3.3% to 30.5%of the phenotypic variation.Nineteen suggestive QTLs and nine significant QTLs concerned with fiber quality traits were detected with explained 4.6%to 25.8%of the phenotypic variation.Out of all QTLs,qSI-1,qLP-1,qFL-2,qFM-1,qFL-5 and qFL-4 were also reported in previously research.Twenty one QTLs were detected in same location/interval or nearby at same loci and with same effects direction in separate analysis and joint analysis.These QTLs with little interaction by environment and stable in different environments are of value for a marker-assisted selection(MAS) program2.A three-way cross segregated population,Zhong164/Zhong12//Difenmian8,and its F_2:3 inbreed lines were constructed.Zhong12 and Difenmian8 were parents of three hybrids, Xiangzamian2,Wanza40 and Zhongza028,and originated from Huanghe River valley.A linkage map was developed for the four-way cross with SSR markers and JOINMAP3.0 software.A linkage map was constructed for the four-way cross with JOINMAP3.0.The map is comprised of 29 linkage groups with 107 mapped loci which span between 1.1cM and 85.9cM.The 107 loci covered 940.1cM,which was approximately 18.8%of the total recombination length of the cotton genome.The average distance between loci was 8.8cM genome wideIn the four-way cross population,Six suggestive QTLs controlled plant branches,leaf chlorophyll content and date of first square were detected with explained 3.2%to 5.6%of the phenotypic variation.Nine suggestive QTLs and six significant QTLs concerned with number of bolls per plant,boll weight,lint percent,number of seeds per boll,seed index, seed cotton yield per plant and lint yield per plant were detected with explained 2.6%to 11.0%of the phenotypic variation.Five suggestive QTLs and three significant QTLs concerned with fiber length,micronaire reading,fiber elongation ratio and fiber uniformity were detected with explained 3.2%to 6.8%of the phenotypic variation.3.After one cycle specific combining ability reciprocal recurrent selection,the means of yield traits of two populations were significantly increased with extent from 1.96%to 26.99%.The range of variation of yield traits was not seen decrease in two improved populations.The data from molecular marker analysis also showed that the genetic variety of improved populations did not decrease than initial populations,and even was increased in some degree.Although recurrent selection populations aroused from primary segregated population of three or four-way cross by many times inbreed and outbreed,selection with single marker or flanking markers were still effective.Means of individuals contained two QTLs were significant higher than that of contained one QTLs when pyramid QTLs of lint percent or boll weight in Pâ… .Means of lint percent of individuals will significantly increase with the number of QTL increase in individuals when pyramid QTLs of lint percent or boll weight in Pâ…¡.But the same case can not be seen when pyramid QTLs of boll weightAssisted with markers linked with QTL,selected individuals to test-cross for next cycle recurrent selection can be done before flowering instead of after boll opening,and can accelerate the procedure of recurrent selection,or conduct test-cross before flowering with distinct goal and more efficacies.