High Density Genetic Linkage Map Construction And QTLs Analysis Of Important Trains In Leymus Chinensis

Leymus chinensis is an important constructive species and dominant species in arid grasslands in eastern Eurasia.L.chinensis has high protein content,good palatability and is called'fine grain in forage'.The developed underground rhizomes of L.chinensis have strong penetration ability,forming a strong root network,which can consolidate soil and maintain water and soil.It is an excellent forage for improving water resources and air quality,curbing the“three modernizations”of grassland ecosystem and modulating hay.Many important traits of forage are quantitative traits.If conventional breeding methods are used to breed new varieties of L.chinensis with high quality,high yield and high resistance,the cycle is long and the efficiency is low.It is very difficult to carry out genetic improvement,and it is vulnerable to the interference of external environment and crop growth cycle,which is far from meeting the needs of social and economic development.For L.chinensis with large genome and complex genetic background,there is still no literature related to genetic map.In this study,eight new strains from different sources with significant differences in morphological traits,nutritional quality and chlorophyll fluorescence coefficient were used for a large number of hybridization.Due to the need of flowering meeting and mapping population,the F₁ population obtained from the hybridization of two materials was used as the material.The SNP marker development was completed by dd-RAD simplified genome sequencing technology,and the true and false species were identified.The genetic map of Leymus chinensis was constructed by the“preudo-testcross”strategy.At the same time,the QTLs related to morphological traits,nutritional quality and chloroplast fluorescence coefficient were located and analyzed.The main results of this study are as follows:1.The hybrid experiment was carried out for two years,143 hybrids were harvested in the first year,seed setting rate was 18.6%,109 hybrids were harvested in the second year,seed setting rate was 15.8%,a total of 252hybrids were harvested in two years.The seed setting rate was 17.3%,and a total of 201 hybrids developed into healthy seedlings after germination.2.A total of 1240194 SNPs were detected in male parent,of which873910 were transition type(Ts),366284 were transversion type(Tv)and Ts/Tv was 2.39;there were 1041019 heterozygous SNPs and 199175homozygous SNPs,with a ratio of 11.71.There were 7805224 SNPs with genotype deletion and 3231461 SNPs with reference.In the maternal genome,a total of 983448 SNPs were detected,including 692099 transition-type SNPs,291349 transversion-type SNPs,and Ts/Tv 2.38;there were 811023heterozygous SNPs and 172425 homozygous SNPs,the ratio was 7.9.There were 7805224 SNPs with genotype deletion and 3231461 SNPs with reference.3.The SNP data of 201 offsprings and 2 parents were processed to count the number of loci with the same genotype as P1 and P2 in the offspring samples.After hybrid authenticity identification,9 false hybrids were removed,and 192 offspring groups were finally obtained.4.After the analysis of population horizontal variation information,a total of 63150 markers in 4 types were obtained by filtering,including 192aa×bb markers,49986 hk×hk markers,6178 lm×ll markers,6790 nn×np markers.5.In the genetic linkage map based on the“preudo-testcross”strategy,the maternal genetic map contains 14 linkage groups,3558 SNP markers,covering 2385.058 c M genome length,and the average distance between markers is 0.67 c M.The male parent contained 14 linkage groups and 3131SNP markers,with the genome length of 2380.56 c M and the average distance between markers of 0.76 c M.By integrating the two-parent linkage map,the two-parent linkage map contained 4065 markers on 14 linkage groups,covering 2303.404 c M genome length,and the average distance between markers was 0.57 c M.6.The morphological characteristics,nutritional quality and chlorophyll fluorescence parameters 101 of 192 parents and their offsprings were analyzed.After independent sample t test,only 12 traits consist of leaf length,leaf shape index,dry-fresh ratio,ash,Cl,crude fatty,total fatty acid,Fm,ABS/RC,DIo/RC,TRo/CSm and REo/CSm were significantly different among parents.The R/qtl scanone function was used to study the 12 traits based on the constructed parents integration map.A total of 36 QTLs were detected in 8 linkage groups.In this study,based on the simplified genome dd-RAD sequencing technology,SNP molecular markers were developed in large quantities at the whole genome level,and the first high-density genetic linkage map of L.chinensis was constructed.QTL analysis was carried out for the first time,and QTLs for some important traits were obtained.The results will provide powerful molecular tools and information support for genetic improvement of L.chinensis.