Construction Of High-Density Genetic Linkage Map And Identification Of Flowering-Related QTLs In Erect Milkvetch

Erect milkvetch is a perennial legume forage crop.Due to its high nutritional value and strong stress resistance,it has become an important leguminous forage in arid and semi-arid regions.But seed yield and harvesting efficiency in erect milkvetch was decreased seriously due to inconsistent flowering-time and many florets.To solve this problem,we conducted QTL mapping of flowering-related traits by high-density genetic map,identification and control the flowering-related genes for directional improvement.In this study,an F₁ erect milkvetch population consisting of 250 individuals was derived from the cross of male and female parent with great difference in morphological characteristics.SLAF-seq was used for construction of the first high-density genetic linkage map in erect milkvetch and QTL mapping for flowering-time,floret number,and inflorescence length.Our main results are as follows.?1?The SLAF-seq was used to develop SLAF markers for the erect milkvetch parents and 250 F₁ progeny individuals,198,621 polymorphism SLAFs were obtained with a polymorphism rate of 41.19%.The average coverage of each SLAF marker was 20.69-fold for the parents and 5.64-fold for the F₁ progeny.For the F₁ population,other than aa×bb segregation patterns were defined as valid polymorphism SLAFs,the valid polymorphic SLAFs number was 57,256.A total of 4,821 SLAFs were used to construct the genetic linkage map after calculating the MLOD value and quality filtering.?2?The final genetic linkage map consists of 8 linkage groups?LGs?and spans 1,395.35cM,with an average distance of 0.29 cM.There were 4,821 SLAFs in the integrated map with10,322 SNP loci.Among 8 LGs,LG7 had a longest distance of 187.03cM and included 547SLAFs.The shortest distance is 151.18cM in LG6,including 771 SLAFs.LG3 and LG6 were the most saturated with an average marker density of 0.20 cM,and the smallest LG was LG8,with an average inter-marker distance of 0.69 cM.The male genetic map contains a total of3,006 markers with total and average map distance 1189.70 cM and 0.40 cM,respectively.The maximum and minimum linkage groups were LG8?map distance 190.56 cM?and LG4?98.21 cM?.The female genetic map contains a total of 2,667 SLAFs with a total and average map distance 1,525.37 cM and 0.57 cM,respectively.The maximum and minimum linkage groups were LG3?map distance 235.5 cM?and LG8?135.65 cM?.?3?Comparative genomics analysis of erect milkvetch with four relative species was conducted with all the SLAFs used in the genetic map.Medicago truncatula?8.71%similarity?was the most similar to erect milkvetch,followed by soybean?7.65%?,chickpea ?7.53 %?,and lupinus?5.21 %?.Erect milkvetch had closer relationship with medicago truncatula.?4?The QTL mapping was conducted based on the flowering-related traits information and genetic linkage map of erect milkvetch.A total of 64 significant flowering-related QTLs were detected,which located on the linkage groups of LG1,LG2,LG4,LG5,LG7,and LG8.Among the 64 flowering-related QTLs,seven were related to flowering-time,19 for floret number,and 38 for inflorescence length.The phenotypic variation of all significant QTLs varied from 9.38%to 19.1%,with the LOD values ranging from 5.01 to 9.71.