Fine Mapping And Molecular Marker Assisted Selection Of QTL In Chromosome 16 Related To Cotton Fiber Quality In Introgression Lines From Gossypium Hirsutum × Gossypium Barbadense

Cotton fiber is the raw material of the textile industry,which plays an important role in the national economy.With the continuous renewal of cotton textile technology and equipment,textile enterprises have greatly requirements for yarn quality and raw cotton quality.It is common goal for breeders to cultivate new breeding materials with excellent fiber quality on the basis of high yield and stability.In the early stage,CSSL MBI7561 with excellent fiber quality selected from BC₄F_3:5 of CCRI45（Gossypium hirsutum）×Hai1（Gossypium barbadense）was used as female parent,backcrossed with its recurrent parents,to construct the secondary segregating populations with two generations(BC₅F₂ and BC₅F_2:3).BC₆F₂ and BC₆F_2:3were constructed by backcrossing single plant containing introgressive fragment of chromosome 16 with recurrent parent CCRI45 on the basis of it.Fine mapping of QTL for fiber quality.Firstly,the important SSR markers CGR6894,Gh056,NAU2749 and NAU5408 linked to QTL of fiber length and strength on chromosome 16 were selected for QTL mapping in BC₅F₂ secondary segregation population.It was further verified that there were QTLs for fiber length and fiber strength near these markers on chromosome 16.According to the results of QTL mapping analysis of fiber length and strength,the marker interval（CGR6894-Gh056）was selected to encrypt the marker,and bioinformatics analysis was carried out on this interval.It was found that there were genes related to fiber development in the annotated genes in this interval.Based on the BC₆F₂ population genotype,an encrypted linkage map of this region was constructed,and QTLs were mapped by combining the phenotype data of BC₆F₂ and the phenotype data of BC₅F_2:3 in two environments.The results showed that the QTL q FL-16-1 related to fiber length could be detected in three populations of two generations.The LOD values were21.17,2.79 and 6.19 respectively,and the phenotypic variation rates were 6.61%,13.59%and 23.35%respectively.The QTL was located between marker CGR6894 and GL16,the physical distance was0.23M,and there were 19 related genes in this interval.A fiber strength related QTL was detected in BC₆F₂ population,with LOD value of 10.94 and phenotypic variation rate of 6.92.The QTL was located between marker GL16 and Gh056.The 6 genes with higher absolute or relative expression in the fine mapping interval were selected by the obtained transcriptome data,which were synthesized into fluorescent quantitative specific primers.With the recurrent parent CCRI45 as control,the expression levels of 6 genes at different stages of fiber development were compared by q RT-PCR experiments.As a result,GB＿D07G0649,GB＿D07G0643,and GB＿D07G0647 were determined as candidate genes,which laid the foundation for the next step of gene cloning and functional verification experiments.In addition,using 4 SSR markers linked with 3 major QTLs for fiber length and 3 major QTLs for fiber breakage ratio on chromosome 16,marker-assisted selection and aggregation effects were studied between the generation BC₆F₂ and BC₆F_2:3.The selected QTLs related to fiber length and strength of chromosome 16 have significant genetic effects in both generations of the land-sea introgression population,and the aggregation effect was significant.A batch of individual plants with good fiber quality have been selected,which laid the foundation for further molecular aggregation breeding.