| Cotton fiber is an important raw material of textile industry. The development of modern textile industry set a higher request on the fiber quality of cotton. Conventional breeding including wide cross breeding has made great contributions on improving fiber quality. However, the complicated genetic basis limted the cotton fiber quality improvement. It is necessary to identify the fiber quality genes (QTLs) by molecular markers and, thereafter, apply in molecular marker-assisted selection (MAS).It is known that the genetic diversity of cultivated upland cotton (Gossypium. hirsutum L.) is limited and there are absent or less of alleles for fiber quality improvement in the germplasm of cultivated upland cotton. And another cultivated allotetraploid cotton, sea-island cotton (G. barbadense L.), whose lint yield is obviously lower than G. hirsutum L. but with remarkable high fiber quality. Luyuan 343 is an introgression line with high-quality fiber gene from sea-island cotton. In this study, genetic linkage map was constructed with the polymorphic SSR markers using a mapping population constructed with Luyuan 343 and Lumianyan 22. A relatively fine mapping of the loci related to fiber quality was carried out based on accurate identification of introgression fragments in genome.The DNA of Luyuan343, Lumianyan 22, F1 and all individuals of F2 population were extracted and 4050 pairs of SSR primers are screened in between the two mapping parents. Total 82 pairs of polymorphic primers were obtained, which accounted for 2.0 percent of all screened primer pairs. There were 78 co-dominant markers, which accounted for 95.1 percent of the polymorphic markers. Among the 82 polymorphic marker loci, 57 loci were assigned in 17 linkage groups with a total genetic distance of 411.6 cM by JoinMap3.0, covering 7.9 percent of total cotton genome. By comparison of PCR bands of the 57 markers in 17 linkage groups among the parents, F1, TM-1, ashimouni(the donor variety of sea-island cotton), total 4 introgression fragments were confirmed in the introgression germplasm. They are chromosomal fragments of chromosome 2, chromosome 9, chromosome 16 and chromosome 18, respectively.32 QTLs associated with fiber quality were detected with software WinQTL2.5 and composite interval mapping in the F2 and F2: 3 generations. 6 QTLs were related to fiber length, 5 QTLs were related to fiber uniformity, 12 QTLs were related to fiber fineness, 5 QTLs were related to fiber elongation and 4 QTLs were related to fiber strength. The effect of most QTLs was confirmed to be the dominant effect or the overdominance effect. The QTLs were anchored in chromosome 2, chromosome 9, chromosome 16 and chromosome 25, which tended to be clustered in a special chromosomal region. qFL-16-1 can be detected in two environments and in both F2 and F2: 3 as well, suggested that this locus should be quite reliable, and it can explain 5.19%～6.51% of phenotype variation. qFL-25-1 is located at chromosome 25, and it can also be detected in two environments of F2: 3. Its efficiency gene comes from Luyuan343 and can explain 7.58% and 8.10% of phenotype variation, respectively. qFM-11-1 can be detected in two environments and in both F2 and F2: 3, it can explain 6.54%～8.54% of phenotype variation and the efficiency gene comes from the Luyuan 343, as well. qFM-2-1 can be detected in two environments of F2: 3, which can explain 5.58%～7.65% of phenotype variation. qFM-23-3 may explain 13.21% of phenotype variation,which is the highest contribution rate among all the loci. qFU-2-1 and qFU-2-2 can be detected in two generations and have very high stability. The contribution rate of qFU-15-1 is 18.82%, and thus has very high potential application value.Single marker analysis of these loci using an advanced generation (F8) breeding population were performed to validate the QTLs identified by the mapping population. The results showed that 30 loci among the total 32 QTLs can be detected in F8 populations. It suggested that quite a few of the QTLs detected in this study have potential value in MAS to improve fiber quality in upland cotton using introgression germplasms. |
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