Analysis Of Genetic Effects And QTL Mapping Of Chromosome Segment Substitution Lines With Excellent Fiber Quality Of Cotton

Cotton fiber has an important role in the national economy and people's livelihood.With the improvement of people's living standards,with the update of industrial technology,along with the development of modern agriculture and the implementation of market supply side reform,the requirements of excellent-quality cotton fiber become more urgent.In this study,the CCRI45 is a popular cultivar of upland with high yield,and the MBI7561 with moderate yield and excellent quality is a chromosome fragment substitution lines constructed from CCRI45 and island cotton.Then F₂ and F_2:3 populations were constructed by CCRI45 and MBI7561.SSR were used to identify genotypes and detecte QTL for main yield traits and fiber quality traits.We also carried out a variety of analysis,including clustering and meta-analysis,interaction analysis,trying to find out regions with important genetic effects on fiber quality.The performance of LP,FL,FS and FM of the MBI7561 were significantly superior than those of CCRI45 in many years.All of the FL were above 31.52mm,all of the FS were above 32.5 cN/tex,and all of the FM were at the A level.In F₂ and F_2:3 populations,the averages of the yield are not significantly lower than those of CCRI45,and the averages of fiber quality traits were significantly superior than those of CCRI45.Except BW,the values of transgressive rate over the recurrent parent about other traits in multi-environments are 53.62%-94.6%,while the values about BW are only17.52%-32.83%.The coefficient of variation of all trait are 0.94%-16.93%.The same traits are very significantly positively correlated in different environments.A total of 81 pairs of markers in 31 fragments of 18 chromosomes were screened out by using 2292pairs of markers in the whole genome high density map.The length of homozygous fragments is 138.11cM,which accounts for the total length of the whole genome is 2.70%;the length of hybrid fragments is86.96 cM,which accounts for the total length of the whole genome is 1.70%;and the background recovery rate is 95.6%.The background recovery rate of F₂ population is 97.30%-99.20%;the length of homozygous fragments in the proportion accounts for the total length of the whole genome is0.94%-2.00%;and the rate of heterogeneous fragments is 0.30%-2.40%.The relevant fragments on Chr01,Chr02,Chr07,Chr16,Chr17,Chr19 and Chr25 are prevalent in the fiber quality outstanding individuals.In the three environments,129 QTL were detected,45 of which were stable in multiple environments.26 were related to the yield traits,and the contribution rates to phenotypic variation were3.39%-30.35%,among which 14 were related to BW,12 were related to LP,and 5 of each traits were detected in more than one environment.A total of 103 QTL were related to fiber quality,the contribution rates to phenotypic variation were 0.28%-13.19%,of which 21 were FL-related,27 were FS-related,18 were FM-related,16 were FU-related,21 were FE-related.The numbers of QTL that were stable in multiple environments corresponding to each trait are followed by 4,11,9,5,6.The hotspots regions of QTL are distributed in the relevant segments of Chr02,Chr07,Chr09,Chr15,Chr16and Chr25,and the QTL in these segments are more effective.In addition,most of the synergistic genes associated with BW came from CCRI45,and most of the synergistic genes associated with LP and fiber quality were from Hai1.A total of 118 QTL were clustered and distributed in 25 QTL-Clusters of 14 chromosomes.The number of QTL-Cluster on each chromosome is 1-5,and the number of QTL in each QTL-Clusteris2-10,mostly 3-5.Each of Chr07,Chr15,Chr16,Chr17,Chr19 and Chr25 contains two or more QTL-Clusters.After meta analysis,a total of 92 related QTL were clustered in 21 Meta-QTL and the remaining 37 QTL were present independently.The numbers of QTL included in each of the Meta-QTL is 1-16.The results of meta-analysis showed that the relevant fragments on Chr07,Chr15,Chr16,Chr17,Chr19 and Chr25 were the hotspot regions.Meta-02-1,Meta-08-1 and Meta-22-3 were the new Meta-QTL detected in this study.And 43 QTL have not been reported in other studies,of which 16 QTL were stable in multiple environments.A total of 380 interactions were detected and distributed on 12 chromosomes.Chr01,Chr09,Chr15,Chr16,Chr19 and Chr25 were the main chromosomes.They show a concentrated distribution in several major fragments,and distributed in the form of bundles between each main segments.The relevant segments on Chr01 is the main effect segments of interaction,which has a wide impact on traits.Interaction effects had the greatest impact on FS,who's number was 68,the average contribution rate was 27.54%,the additive-additive effect values were between-1.51-2.19,the dominant-additive effect values were between-3.27-8.01.The effect of interactions on FM was minimal,although there were a certain amount,the effect values were very small,the average contribution rate was 17.17%,additive-additive effect values were between-0.53-0.34,dominant-additive effect values were between-0.55-0.81.Based on the above results,the genetic effects of the segments were analyzed.The relevant chromosome substitution segments of Chr07,Chr15,Chr16,Chr19 and Chr25 were selected as the important effect sites.This indicates the direction for QTL fine mapping and lays the foundation for post-gene cloning...