Development Of Chromosome Segment Introgression Lines From Gossypium Turneri Fryx Into Gossypium Hirsutum

Wild cotton has been in a poorly natural environment for a long time and contains a large number of excellent genes.The transfer of excellent genes from wild cotton to cultivated cotton is an effective way to broaden the genetic basis of Upland cotton（Gossypium hirsutum）and increase the genetic diversity of Upland cotton.Gossypium turneri Fryx(2n=2x=26,D₁₂ D₁₂)is a diploid wild species,which originated in Baja California,Mexico with the plant height of about 70 cm and grows in a poorly malnutritional soil.It has the excellent characteristics such as early bracts falling,insect resistance,salt and drought tolerance.Through hybridization and multiple backcrossing,the excellent characteristics of Gossypium turneri Fryx can be transferred into Upland cotton,which will greatly broaden the genetic basis of Upland cotton and develop new cotton germplasm.In this study,based on the previous research,combined with molecular marker-assisted selection,we developed a set of chromosome segment introgression lines from Gossypium turneri into Gossypium hirsutum.The main results are as follows:1.Screening and development of polymorphic molecular markers between recipient and donor parentsA total of 1378 molecular markers were screened using G.australe-,G.raimondii-and G.arboreum-specific markers,74 polymorphic markers were obtained.A total of 7569 pairs of SSR primers were designed based on the genomic sequence of Upland cotton and G.turneri Fryx.352 pairs of primers were selected and synthesized for polymorphism according to the distribution of primers on the chromosome.A total of 177 polymorphic markers were obtained.The number of markers on each chromosome is not the same among the 251 molecular markers.D02,D05 and D13 each have the largest number of markers with 22;D12 has the least number of markers with 12.The marker density on each chromosome is different with the maximum marker density of 2.70 Mb/marker on D03 chromosome and the minimum marker density of 4.51 Mb/marker on D11 chromosome.Only 77 markers were found on introgression fragments.2.Chromosome segment introgression analysis from G.turneriA total of 251 polymorphic molecular markers were employed to identify alien chromosome segments in 857 BC₃F_2-4,BC₄F₁ and BC₄F_2-3 individuals.The result showed that 693 individual plants had chromosome segments from G.turneri Fryx.The total length of introgression fragments accounted for 32.72%of the D subgenome of Upland cotton.D08 chromosome coverage is the highest with 90.19%.There were 3405 introgression fragments distributed in 693 lines.The total length of the introgression fragments was 14996.08 Mb,18.07 times of the total length of the chromosome of the Upland cotton D subgenome.The shortest introgression fragment is 0.22 Mb and the longest length is 30.23 Mb.Each line contains 4.91 introgression fragments on average.The number of introgression fragments of each line arranged from 1 to 17,most lines have less than 7 introgression fragments.And 143 lines with single introgression fragment,accounting for 20.63%;130 with two introgression fragments,accounting for 18.76%.Among them,one line was found with up to 17introgression fragments.3.Phenotypic variation of introgression linesField observations showed that the introgression lines were obviously different from Upland cotton TM-1 in stem diameter,plant height,leaf size,boll shape,plant type,and pedicel.Line D2324 is with large leaf,and Line D2453 is dwarf;Line D2571 has a long pedicel.Line D2277 has long fruit branches with big angle between fruit branches and main stem.Line D2282 shows sharp bolls and Line D2321 shows open-bud.The fiber quality collected from Shangqiu in 2020 was examined.Line D2433 showed its elite fiber quality with 33.44 mm of fiber length,33.80 cN/tex of fiber strength,and 4.15of fiber micronaire value;Line D2498 exhibited 32.99 mm of fiber length,32.70 cN/tex of fiber strength,4.99 of fiber micronaire value is;While the Upland cotton TM-1 was 31.00mm of fiber length,26.75 cN/tex of fiber strength,and 4.77 of fiber micronaire value.4.Correlation analysis of phenotypic traits of introgression linesCorrelation analysis showed that seed index and single boll weight,plant height and fruit branche number or boll number,fruit branch number and boll number,fiber length and fiber strength all have extremely significant positive correlations,but fiber length,fiber strength and fiber micronaire value all have extremely negative correlations.5.QTL mapping analysis of introgression linesThe QTL Ici Mapping software was used to perform QTL analysis on 282 introgression lines in Shangqiu 2020.Preliminary analysis found that 6 traits are associated with 9 markers.Plant height,seed index,boll weight,fiber length,and fiber strength each are associated with one marker.fiber micronaire values are associated with four markers.