Development Of Chromosome Segment Introgression Lines From Gossypium Raimondii Into Gossypium Hirstutum Acc.TM-1

Cotton is one of the most important cash crops in the world,and its fiber is a dominating raw material in textile industry.Upland cotton is the main cultivated variety because of its high yield,good adaptability and excellent fiber quality,and Upland cotton fiber accounts for about 95%of the world’s total production.However,the genetic background of upland cotton has became narrow due to the long-term selection of one or several traits,resulting in the difficulty of simultaneous improvement of multiple traits in modern molecular breeding.Gossypium raimondii is a diploid wild cotton species with low fiber yield,but good fiber quality and stress resistance.If the elite traits of Gossypium raimondii were introduced into upland cotton cultivars,the genetic background of upland cotton could be broadened,which would lay a foundation for biological genetic research and breeding of new varieties.Based on previous studies,a set of chromosome segment introgression lines from Gossypium raimondii into Gossypium hirsutum was constructed by combining modern molecular biotechnology with traditional breeding techniques.The results are as follows:1.Development of polymorphic primers between parents.Using the sequencing data of G.hirsutum TM-1 and G.raimondii,11710 pairs of InDel polymorphic primers were developed.Based on the distribution of these primers on chromosomes,we selected 401 pairs of InDel primers for synthesis.After SDS-PAGE electrophoresis,all 401 pairs of primers showed clear bands difference among two parents.These primers were evenly distributed on the D sub-genome of TM-1,with average distribution density of 2.02 Mb.Of them,D02 and D04 had the highest distribution density,with the average distance of 1.77 Mb,and D01 had the lowest distribution density with the average distance of 2.35 Mb.2.Introgression analysis of G.raimondii chromosome segmentWe used 401 pairs of specific primers to identify alien chromosome segments of 441 BC3F2,BC4F2,and BC5F2 individuals.The result showed that 369 individual plants were found to have chromosome segments of G.raimondii.The introgressed segments involved all chromosomes of D subgenome of TM-1.72 individual plants were not found introgressed segments.The total coverage rate of introgression segment from G.raimondii is 42.78%.The coverage on each chromosome is different.The coverage rate of Chr.D1 was the highest(84.27%)and that of Chr.D7 was the lowest(4.65%).The coverage rate of Chrs.D4,D5,D6,D8 and D12 was higher than 50%,which was 67.44%,53.17%,79.11%,54.04%and 66.67%respectively.The coverage rate of the remaining 6 chromosomes,D2,D3,D9,D10,D11 and D13,were 13.10%,34.32%,45.43%,20.87%,18.17%and 16.63%respectively,indicating that it is difficult for these six chromosomes to recombinate between parents.A total of 1221 introgressed segments were identified from 369 out of 441 individual plants.The average number of introgressed segments per line was 3.31.The total length of all introgressed segments was 2652.08 Mb,ranging from 0.004 to 12.78 Mb,with the average length of 2.17 Mb.3.Number analysis of introgressed segmentsAmong 369 individuals of intrigression lines,number of introgressed segments was different.The number of introgressed segments per plant ranged from 1 to 14.Segment number of 233 individuals was 3 or less,accounting for 63.14%of the total introgressed individual plants.There were 90 single-segment introgression plants,and the other 80 plants with two introgression segments and 63 plants with three introgression segments.4.Morphological variation of BC3F2,BC4F2,and BC5F2 generationsThough field phenotypic traits survey,we found that many introgressed plants had significant differences in phenotypic traits relative to the recurrent parent TM-1.They displayed some of the unique phenotypes of G.raimondii,such as petal red hearts,yellow anthers,dense trichome on leaf and stems,large fruit bells,andhigh plants,or intermediate phenotypes of parental traits,such as the degree of petal red hearts,the degree of the bell,the size of the bell,and the like.5.Statistical and correlation analysis of yield and fiber quality related traits.The yield and fiber quality related traits of i were investigated in Dangtu,Anhui Province,in 2017 and 2018,respectively.The investigated traits included boll weight,seed index,lint percentage,fiber length,fiber strength,micronaire value,fiber uniformity,fiber elongation,plant height,number of fruit branches and bolls.The mean values of all traits in both environments were close to recurrent parents TM-1.The correlation analysis showed that,in both environments,boll weight and seed index were significantly positively correlated;seed index and lint percentage were significantly negatively correlated;fiber length was positively correlated with fiber strength,fiber uniformity and elongation;fiber length was negatively correlated with micronaire value,fiber strength and micronaire value;fiber strength was positively correlated with uniformity and elongation;There was a very significant positive correlation between uniformity and elongation.In the second environment,the number of fruit bolls was positively correlated with the number of fruit branches,and the plant height was positively correlated with the number of fruit branches and the number of fruit bolls.6.Preliminary identification of agronomic traitsAccording to the investigation of field phenotypic data,22 introgression lines(ILs),named IL-G.r-1 to IL-G.r-22,respectively,with improved phenotypic traits,were selected.Among them,there are 6 ILs with high lint percent,ranging from 38.25%to 39.67%;5 ILs with high boll weight,ranging from 31.67 to 38.83 bolls;3 ILs with long fiber length,ranging from 31.04 to 31.28 mm;4 ILs with strong fiber strength,ranging from 33.27 to 36.6 Cn/tex;and 7 ILs with good micronaire value,ranging from 4.00 to 4.14.Three of these ILs were improved in two characters at the same time.The lint percentage and micronaire value of IL-G.r-5 were 38.25%and 4.08,respectively;the fiber length and micronaire value of IL-G.r-9 were 31.04 mm and 4.05;and the lint percent and fiber length of IL-G.r-22 were 39.67%and 31.05 mm,respectively.