| The cotton production and the derived industrial chain have been playing a very important role in the economic development of China and the development of modern textile industry sets a higher request on cotton fiber quality. Wide cross breeding had made great contributions on improving fiber quality. However, substantial increase in fiber quality must rely on molecular breeding. Molecular maker assisted selection with the DNA makers linked with QTLs of fiber quality and yield related traits would increase the effeciency of cotton breeding.The genetic diversity of cultivated upland cotton (Gossypium. hirsutum L.) was limited due to long-term artificial selection in breeding. The crop yield, adaptability and further improvement of quality traits are facing great challenges. There are absent or less of alleles for fiber quality improvement in the germplasm of cultivated upland cotton. However, another cultivated allotetraploid cotton, Sea Island cotton (G. barbadense L.), whose lint yield is obviously lower than upland cotton (G. hirsutum L.), but with remarkable high fiber quality. Luyuan 343 is an introgression line with excellent quality fiber genetic components from Sea Island cotton, while Lumianyan 22 is a fine cotton variety characterized by higher fiber quality. In this study, genetic linkage map was constructed with the polymorphic SSR markers using a mapping population constructed by 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.A total of 8150 pairs of SSR primer were used to screen polymorphism between Lumianyan 22 and Luyuan343, which resulted in 150 pairs of polymorphic primer, and the polymorphism primer accounted for 1.84 percent of the screened pairs. Because of more recent genetic relationship between the parents, their polymorphism was relatively low. There were 140 co-dominant markers, which accounted for 93.33 percent of the polymorphic markers, while there were 10 dominant markers. Based on the previous data in our lab, 230 of them were applied to screen the F2 population containing 209 individuals. Linkage test (LOD=6.5) indicated that 196 polymorphic loci derived from 230 primer pairs could be mapped into 33 linkage groups and covered a total genetic distance of 1071.449 cM, approximately 20.60 percent of cotton genome.To determine the introgression fragments from Sea Island in luyuan343, all of the 196 polymorphic primer pairs in 33 linkage groups were served to compare their PCR bands among the two parents, TM-1, which is widely used as the standard genetic line of upland cotton and Ashimouni, which is the donor Sea Island cotton parent of the introgression line, Luyuan343. Total of 120 introgression marker loci were detected, which were distributed in 25 linkage groups and covered a total genetic distance of 358.131 cM, approximately 6.89 percent of cotton genome. Most of introgression fragments and introgression loci were proved to be distributed in chromosome 16, chromosome 2, chromosome 3 and chromosome 18, and there was only one introgression locus in some chromosomes or linkage groups, such as Chr5, Chr7, Chr13, LG18, and so on.53 QTLs associated with fiber quality were detected with software WinQTLCartographer2.5 by Compose Interval Mapping (CIM) method in three data sets, F2, F2:3HN and F2:3LQ. 7 QTLs were associated with fiber length, 8 QTLs were related to fiber uniformity, 13 of the QTLs were for fiber micronaire and 12 were for fiber elongation. The numbers of QTL for lint fiber strength percentage and lint percentage were 5 and 8 respectively. The QTLs were anchored in chromosome 2, chromosome 7, chromosome 16, chromosome 17, and chromosome 23, which tended to be clustered in a special chromosomal region. qFL-7-1, which explains 14.36%, 7.71% and 10.07% of phenotype variation and the efficiency genotype comes from Luyuan 343, can be detected in three data sets, and qFS-7-1, whose efficiency genotype comes from Luyuan 343 as well, explains 27.25%, 10.86% and 28.16% of phenotype variation in three data sets respectively. The results indicated that both the loci which were in DC40182 and CGR6773 interval on chromosome 7 were quite reliable and therefore has very high potential application value. Meanwhile, QTLs associated with fiber uniformity, fiber micronaire, fiber strength and lint percentage were clustered between DC40182 and CGR6773 interval, which indicates that the chromosomal segment in chromosome 7 might play key role on fiber traits.44 QTLs were detected to be associated with introgression fragments and introgression loci, accounted for 83.02 percent of total QTLs in this study, including 5 for fiber length, 8 for fiber uniformity, 9 for Micronaire value, 12 for fiber elongation, 4 for fiber strength and 6 for lint percentage.Therefore, we were concluded that the majority of genetic components conferred favorable contributions on excellent fiber quality in the genome of introgression line of upland cotton were the introgression chromosomal fragments or intrgression loci from Sea Island cotton. Further identify the introgression genomoic components and consequently evaluate their genetic effects on fiber quality related traits by molecular markers will be great benefit on MAS in upland cotton breeding. |
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