| Cotton is an important cash crop in the world. A long-term challenge facing cotton breeder is the simultaneous improvement of yield and fiber quality to meet the demands of the cotton producer as well as the textile industry. In the recent years, improvement of cotton fiber quality has been extremely important because of changes in spinning technology. However, a negative association between lint yield and fiber quality are still presented after over dozens years of exhausting breeding for improved fiber properties due to the genetic complexity of fiber quality properties. Conventional breeding procedures exist difficulty in further improving fiber quality because of its high costs, long duration, and low selective efficiency. The development of DNA markers linked to the fiber quality QTL would allow cotton breeders to trace this very important trait in early plant-growing stage or early segregating generations. The use of these DNA markers is increasing the prospect for streamlining the cotton breeding programs for improving fiber quality while maintaining fiber yield.However, QTL analysis for fiber properties is problematic for several reasons: (1) RFLP with complicated procedure and high cost were used in majority of previous reports. It is very hard to use it directly in MAS programm; (2) QTLs obtained from interspecies population of Sealand cotton and Upland cotton showed less valuable in improving fiber quality of Upland cotton; (3) In previous reports, population constructed were all F2 population. Replicated experiment couldn't be carried out. Analysis of epistasis and QE interaction effect remains to be difficulty. Considering of these problems above, the objective of this research is to determine the presence of common QTL associated with a given trait across different background; to develop a RIL population and identify stable QTL over environments; to analysis AA and AE interaction effect; to preliminary study on MAS on fiber strength.1. QTLs mapping for fiber properties under different back groundingUsing three elite fiber strains of upland cotton (Gossypium hirsutum L.) as parents, three F2 linkage maps were constructed. They covered 666.7cM, 557.8cM and 588cM, approximately 14.82%, 12.4% and 13.07% of the total recombinational length of the cotton genome, respectively. There are 38 QTLs for fiber traits in which 11 QTLs were for fiber length, 10 for fiber strength, 9 for micronaire, and 8 for fiber elongation detected by composite interval mapping. Among them, 15 stable QTLs (39.47%) could be found in F2 and F2:3 simultaneously. At least 3 QTLs could be identified at two populations. Characterization of identical QTL at different populations indicates exiting elite fiber gene have possibly the same origin. In addition, we found three pairs of putative homoeologousQTLs, qFL-7-1c and qFL-16-lc, qFS-D03-la and qFS-A02-lb, qFS-A02-lc, and qFE-D03-la and qFE-A02-lc. It was assumed recombinational event occurred randomly in A or D subgenome homoeologous region during the process of introgression.2. Development a RIL population and QTLs mapping for fiber quality and yield traits under different environmentsBy means of bulk-selfing method, a RIL population was developed from individuals of (7235 TM-1) F2 in Upland cotton. Repeated experiment was conducted at two locations in 2002 and 2003. Wide variation occurred among RI lines and transgressive segregation was observed across all environments for all traits. The total of 110 SSR loci was grouped into 27 linkage group and covered 810.07 cM, approximately 18.02% of the total recombinational length of the cotton genome.A total of 35 QTLs for fiber quality and 25 QTLs for yield traits were detected in two or four environments independently. Thirty QTLs were found in the joint analysis based on means over two or four environments. QTLs obtained based on means over several environments seems to provide the best strategy for obtaining stable QTL.Most QTLs for fiber quality and yield traits were located at the same interval or neighbor interval, especially at LGD03. |
PDF Full Text Request