Construction Of Chromosome Segment Substitution Lines And Primary Qtlmapping In Early-maturing Upland Cotton

The performance of the fiber quality and the resistance to verticillium of G. bardadense cultivars is superior to G. hirsutum. It is important for cotton genetic improvement to introgress excellent traits genes from G. bardadense to early-maturing and high-yield G. hirsutum cultivars . In this research, a BC5 population with genetic background of G.hirsutum cultivars and a little of chromosome segments of G. barbadense cultivars were developed through crossing and backcrossing between early maturity Upland CCRI36 as the recipicent parent and island Hai1 as the donor parent by SSR microsatellite marker-assisted selection (MAS). The genetic background of 133 BC5F1 lines and 303 BC5F2 individuals were detected using 391 pairs of polymorphic marker which were selected from the BC1F1 genetic linkage map formerly constructed in our Lab based on one marker about 5-10cM, then the results of phenotypic identification and molecular detection of lines and individuals were used to detect and analyze the QTL for the fiber yield,quality and resistance to verticillium. These research results will play the importance in molecular breeding.Plenty of lines and individuals superior to the recipicent parent CCRI36, especially in fiber quality were acquired through the fiber yield and quality analysis. The transgressive rate of BC5F1 and BC5F2 lines over the recurrent parent CCRI36 is above 30% in fiber length,strength and micronaire, and the rate of BC5F2 individuals is above 40% generally. There were large number of high fiber quality individuals, 65 and 55 individuals is above 32 cN/tex of fiber strength in BC5F2 lines and BC5F2 excellent lines , the highest fiber strength reached to 37.8 cN/tex.Through advanced backcrosses, the BC5F1 lines retained plentiful chromosome segments of Hai1. There were 12 to 52 donor segments in the lines with the average of 30.6 , which covered from 191.8cM to 843.3 cM of cotton genome with the average size of 440.9cM, covered 13.3% of cotton genome detected. The holistic genotype analysis showed that the chromosome segments of G. barbadense in the introgressive lines covered the whole genome of G. barbadense and the lines contained abundant genetic informations of G. barbadense.The detection of genetic background of 303 individuals in BC5F2 excellent lines indicated that the genetic background of the BC5F2 individuals was almostly returned to the background of recurrent parent CCRI36. The average substitution rate of chromosome of the recurrent parent in the BC5F2 individuals was 98.1%, near to theoretical value 98.4%. The genetic background of 10 individuals (3.3%) was completely returned to that of CCRI36. The number of remained G. barbadense chromosome segments was mainly about 3-10, there were 11 individuals (3.6%) with only one chromosome segment of G. barbadense, 22 individuals (7.3%) with two chromosome segments of G. barbadense. Through advanced backcrosses, the length of chromosome segment of G. barbadense in the BC5F2 individuals was very small and the length was focused on 6-15 cM, the average length of chromosome segment of G. barbadense of 144 individuals (47.5%) was less than 10cM.Through the analysis above, it could be known the remained chromosome segment of G. barbadense is enough to be small in number and length through 5 backcrosses.A total of 48 QTLs in BC5F1 lines and 56 QTLs in BC5F2 individuals for the fiber yield,quality and resistance to verticillium were detected separately by CIM and one-way analysis of variance with trait and marker. The most of QTLs were minor genes, which could explain 2.75%-16.44% of phenotypic variation. The synergistic effect of fiber quality QTL mainly come from G. barbadense, only one from G. hirsutum in 17 QTLs of fiber strength. Therefore, It was important for cotton fiber quality improvement to introgress chromosome segment from G. bardadense Hai1 to G. hirsutum CCRI36 .There were 31 QTLs detected by the other researchers, which showed the stability of these QTLs in different genetic populations and environments .The stability of high fiber quality individuals were verified in 2009. The fiber strength for 3 materials were above 32cN/tex for two years, which provided fine quality materials for basic research. The fiber quality QTLs linkaged tightly with marker NAU3813b,NAU4928,HAU746,NAU2026,NAU1127,BNL3995,CIR175,NAU2651,BNL1079 and NAU859 were widely distributed in the chromosome segment of G. barbadense in the introgressive individuals with high fiber quality and the synergistic effect of these QTLs was from Hai1. These substitution materials with excellent fiber quality genes will play important effect for the study of functional genomics and molecular breeding in cotton.