Development Of Chromosome Segment Introgression Lines From Gossypium Australe Into Gossypium Hirsutum

The long-term artificial domestication and selection have led to a narrowing of the genetic basis of Gossypium hirsutum cultivars.Wild species contain beneficial characteristics such as resistance to diseases and insects and tolerance to environmental stress.In order to broaden the genetic basis of Gossypium hirsutum,we introduced favorable genes from wild species into cultivars and created new Gossypium hirsutum germplasms with excellent genes of wild species,which are of great significance for enriching cotton germplasm resources.Gossypium australe(2n=2x=26,G2),a wild species,belongs to Malvaceae,Gossypium.G.australe distributes in the western part of Oceania,the perennial shrub has slender stems and dense white pubescence on the stems and leaves.The leaves are broadly oval,margin entire,and the nectaries are dark red.The outer glands of the bract are sunken,bright red,and the bracts are needle-shaped.The petals are lilac,the anthers are red,and the petals are closure and the flowers belong to cleistogamie type flowers.Cotton fiber belongs to brown fiber.Due to the distant genetic relationships between Gossypium australe and Gossypium hirsutum,it is generally difficult to exchange chromosomes between them.Therefore,the chromosome exchange between Gossypium australe and Gossypium hirsutum is promoted by radiation mutagenesis,and the transfer of Gossypium australe genes to Gossypium hirsutum is realized.Based on previous research,using molecular marker-assisted selection,a set of chromosome segment introgression lines from Gossypium australe into Gossypium hirsutum was constructed through multiple generations of continuous selfing.The specific results are as follows:1.Development of Gossypium australe specific molecular markerMISA software was used to search 106352 SSR loci in Gossypium australe genome,and 6099 pairs of SSR primers were developed through electronic PCR screening.A total of 166 pairs of primers were selected and synthesized according to chromosome marker distribution.PCR verification showed that 45 of them could be used for molecular marker identification of Gossypium hirsutum-Gossypium australe introgression lines,accounting for 27.11%.2.Distribution of molecular markers in Gossypium australeThe study showed that among all 217 polymorphic molecular markers specific to Gossypium australe,the number of molecular markers distributed on each chromosome was different,and the number of molecular markers distributed on Gau_chr01 chromosome was the largest,with 31 pairs.Gau_chr09 chromosome has the least distribution,with 9 pairs.The molecular markers used have different distribution densities on chromosomes.The chromosome with the highest distribution density is Gau_chr01 with an average distance of 4.44 Mb.The chromosome with the lowest distribution density is Gau_chr08,with an average distance of 13.05 Mb.Among them,79 molecular marker chromosome segments were introgressed,accounting for 36.41%of the total marker number.3.Identification of chromosome segments markers in Gossypium hirsutum-Gossypium australe introgression line libraryIn this study,217 Gossypium austral-specific molecular markers were used to identify 201 families of BC1F5.A total of 197 families had introgression of alien chromosome segments.The total length of introgressive segment accounts for 32.92%of the Gossypium australe genome,of which the Gau_chr06 chromosome with the highest coverage is 72.74%,and the Gau_chr07 chromosome with the lowest coverage is 0.30%.Chromosomes with coverage between 40%and 60%are(from large to small):Gau_chr09,Gau_chr08,Gau_chr01,Gau_chr04,Gau_chr11,58.99%,51.07%,49.91%,49.32%,and 43.83%respectively.The introgression lines population contains 676 introgression segments of chromosomes from donor parent Gossypium australe,with a total length of 6808.91 Mb,which is about 3.96 times of the genome of Gossypium australe.The length of introgressive segments is the shortest 0.10 Mb and the longest 37.08 Mb.Each family contains an average of 3.43 alien chromosome introgression segments.At the chromosome level,Gau_chr08 chromosome contains the longest introgressive segments with a total length of 2435.11 Mb and 107 segments,involving 102 introgressive lines with a length of 10.30-37.08 Mb.Each introgressive line contains an average of 1.05 segments and 1-2 introgressive segments.Gau_chr10 chromosome contains introgressive alien segments with a total length of 37.51 Mb and 6 introgressive segments,involving 4 introgressive lines,with introgressive segments of 2.67-8.04 Mb in length,and each introgressive lines contains 1-2 introgressive alien chromosome segments.What is special is Gau_chr07 chromosome,which has only one introgression lines and contains two introgression segments of alien chromosome,with the total length of introgression segments being 0.34 Mb.We analyzed the number of alien chromosome segments in introgression lines,ranging from 1 to 12,of which most introgression lines contain less than 5 segments,26 lines with single introgression,accounting for 13.20%;There were 43 lines with double segments introgression,accounting for 21.83%.Thirty-seven lines(18.78%)were introgressed by the three segments.The number of segments with the most introgression is 12,with 1 line.4.Phenotypic variation of introgression linesPhenotypic identification showed that there were obvious differences between some introgression lines and their parents Gossypium hirsutum.For example,introgression lines HR039-1 has long and narrow bracts,which are obviously different from Gossypium hirsutum.The introgression lines S1966 has a longer pedicel.The introgression lines S2034 showed virescent,yellowish leaves and short plants.There are very few organ pigment glands such as leaves,bolls,bracts and sepals in the introgression lines S1938.5.Correlation analysis of phenotypic traits of introgression linesThe correlation analysis of botanical characters of cultivated Gossypium hirsutumGossypium australe introgression lines was carried out.The results showed that there was a very significant positive correlation between seed index and single boll weight,Pearson correlation coefficient was 0.417;The seed index was negatively correlated with lint percentage,Pearson correlation coefficient was 0.566;There was a significant positive correlation between lint percentage and boll number,Pearson correlation coefficient was 0.488.There was a very significant positive correlation between the number of fruit branches and the number of bolls,and Pearson correlation coefficient was 0.458.Single boll weight was positively correlated with plant height,lint percentage and fruit branch number,plant height and fruit branch number.There was a negative correlation between seed index and fruit branch number,seed index and boll number,single boll weight and lint percentage.6.Evaluation of excellent materials of introgression linesGossypium australe,a wild species,has the characteristic of improving lint percentage.In this study,19 high-lint-percentage introgression lines were screened from the introgression line library,with the lint percentage ranging from 39.53%to 44.85%,higher than that of the recipient parent Gossypium hirsutum(31.20%).