Identification Of Introgression Lines From Gossypiumhirsutumrace Latifoliumacc TX-48 In G.Hirsutumacc TM-1 (A Standard Line) And Mapping Of QTLs For Agronomic Traits

Cotton is one of the most important fiber crops in the world,especially has a pivotal position in textile industry.Along with the development of society and economy,people pursue high yields and high quality of fiber on cotton production at the same time.Therefore,the development of high quality cotton varieties becomes urgent increasingly.In conventional breeding intraspecific hybridization method was employed to aggregate favorable genes into one cultivar toimprove yield and quality.However,with the overuse of relatively few Upland cotton cultivars,breeders found it was very hard to make breakthough in breeding and cotton breeding has reached a plateau period.Cotton gene bank contains 46 wild species and 4 cultivated species.Each cultivated species has its feral types,which posess diverse desirable genes that could be transferred to cultivars for cotton breeding.But in the process of genes introgression,drag of linkage would happen.To break the linkage drag,development of segment introgression lines through intraspecific hybridization could be of high efficiency.In addition,mapping of QTL for important agronomic traits would provide the foundation for future cotton breeding.G.hirsutum race latifolium is one of the important varieties of semi-wildupland cotton;it contains a lot of disease resistance,insect resistance,stress tolerance and so on.It has a closed genetic relationship to the cultivars of Upland cotton.So developing chromosome segment introgression lines by G.hirsutum race latifolium is feasible and valuable.In this study,upland cotton genetic standard line TM-1 used as the receptor parent,upland cotton feral landrace,TX-48(G.hirsutum race latifolium acc TX-48)used as the donor parent to perform the development of introgression lines.BC3F2 generation was identificated for chromosome introgression by marker-assisted selection(MAS).1.Identification of introgression linesin BC3F2 of TM-1×TX-48This introgression lines was constructed by crossing G.hirsutum acc.TM-1 as recipient parent crossed withG.hirsutum race latifolium acc.TX-48 as donor parent.BC3F2 population produced contained 691 individurals from 66 BC1 families.Total of 230 polymorphism markers mapped on 49 linkage groups were used to genotype BC3F2 individuals.The introgression lines covered 1971 cM of the present map,approximately 42.3%of the total recombination length of the cotton genome.The average number of introgressed homozygous segments is 3.1,ranging from 0 to 15.The longest introgressed segments is 28.8 cM,the shortest is 0.5 cM.Due to lowergenetic polymorphism between G.hirsutum,SSR markers available were not enough for identification of introgression lines,which is necessary to develop new markers for effective identification of introgression.2.QTLfor yield and quality traitsTwo population of BC3F2:3 and BC3F2:4 were employed to mine QTL for yield and fiber quality using single marker analysis.A total of 62 QTLs were found,50 QTLs of them in BC3F2:3 population.No QTL was detected for boll weight.The position of 8 QTLs was undetermined.Twenty-six QTLs was positive additive and 24 QTLs was negative.All 12 QTLs of micronaire was negative.In BC3F2:4 population,12 QTLs were detected.No QTL for fiber strengh was detected.Nine QTLs was positive additive and three QTLs was negative.There are 4 QTLs unmapped.The results showed that the QTLs for micronaire were negative additive,implying beneficial for the improvement of cotton fiber quality.In BC3F2:3 population,11 QTLs for lint percent,2 QTLs for seed index,12 QTLs for fiber length,6 QTLs for fiber strength,12 QTLs for micronaire,7 QTLs for fiber elongation were detected.In BC3F2:4 population,one QTL for boll weight,4 QTLs for lint percent,one QTL for seed index,3 QTLs for fiber length,one QTL for micronaire and 2 QTLs for fiber elongation were detected.Meanwhile,using the likelihood ratio QTL,the result indicated the majority of QTLs can be found in single marker analysis but 4 QTLs.3.Creation of elite introgression linesAccording to the result of BC3F2:3 and BC3F2:4,total of 13 lines showed the significant improvement in agronomic traits respectively,namely,8 for fiber strength,3 for fiber length and 2 for lint percentage.