| Heterosis utilization is the main approach to crop improvement.The genetic basis of heterosis has been studied widely and deeply in maize,rice,rape and other crops.In recent years,although the great progress has been made in the heterosis utilization of flax(Linum usitatissimum L.),which the technology system of two-line flax heterosis utilization has been developed for the first time and the production and application of flax hybrid have been realized,the studies on genetic basis of two-line flax heterosis are still relatively weak.Therefore,this study was conducted to focus on the relationship between combining ability and flax heterosis,the genetic effects of yield-related traits and QTL mapping of heterosis-related traits in two-line flax hybrid.The objective was to reveal the genetic basis of two-line flax heterosis and to provide theoretical basis for further improving the utilization efficiency of two-line flax heterosis.The main results are as follows:1?A incomplete diallel cross using eighteen flax genotypes including seven thermo-sensitive male sterile lines and eleven restorer lines with 77(7×11)hybrids was carried out to estimate effects of the general combining ability(GCA),special combining ability(SCA)and heterosis for fourteen main agronomic and quality traits in two-line flax hybrid.The results indicated that the variances for studied traits were significantly differences among the genotypes.GCA effects was significant rather than SCA effects for most traits,including plant height,technical length,branches per plant,stems per plant,seeds per capsule,1000-seed weight,oil content,oleic acid,linoleic acid,stearic acid and palmitic acid.The heredity of these traits was mainly controlled by additive genes.Both GCA and SCA effects were significant for some traits,including capsules per plant,yield per plant,and linolenic acid.The heredity of these three traits was controlled by additive and non-additive genes,of which the additive genes played a dominant role.The heterosis over male parent and over control cultivar were widely observed in seventy-seven hybrid combinations.The correlation analysis revealed that heterosis of main agronomic and quality traits in two-line flax hybrid was significantly related to general combining ability(GCA)and specific combining ability(SCA).Both or one of parents has high GCA or have high SCA in strong heterosis combinations.Meanwhile,the parental GCA was significantly greater than SCA,and the GCA in restorer lines was significantly greater than in male sterile lines.Hence,the heterosis in two-line flax hybrid was closely related to the general combining ability(GCA)and special combining ability(SCA).Selection for parental general combining ability(GCA)was the key of parent selection in two-line flax cross breeding program.2?The four basic populations(P1,P2,F1 and F2)derived from two crosses respectively were made for genetic analysis of yield-related traits in two-line flax hybrid using major gene plus polygene mixed inheritance model.The results indicated that yield per plant,capsules per plant and 1000-seed weight were all controlled by two major genes with additive-dominance-epistatic effects plus poly-genes with additive-dominance effects,and seeds per capsule were controlled by two major genes with additive-dominance effects plus poly-genes with additive-dominance effects in two crosses.In the F2 populations,the major gene heritability of yield per plant,capsules per plant and seeds per capsule in two crosses were 43.50%-73.28%,those of 1000-seed weight was 10.55%-34.40%.A conclusion could be made that additive,dominance and epistatic effects of major gene and ploygene could play important role in inheritance of yield-related traits in two-line flax hybrid.For utilization of two-line heterosis in flax,not only additive effect,but alse dominance effect could be used more efficiently to increase hybrid flax production in the future.3?Based on a F2 mapping population derived from the two-line hybrid combination "1S×Longya10",the specific-locus amplified fragment sequencing(SLAF-seq)was used to construct the SNP high density genetic linkage map and QTL mapping of two-line flax heterosis.The results show that there are 23,170 SLAF tags with polymorphism in a total of 286,776 SLAF tags developed in this study.The ratio of polymorphic SLAF tags was 8.08%.After strict screening and filtering,811 SLAF tags were finally obtained for construction of flax molecular genetic map.A high density genetic linkage map of flax with 15 linkage groups and a total length of 1495.89 c M was successfully constructed by using High Map software.The average distance among the markers was 1.84 c M,and the number of polymorphic SNP loci was 1344.Based on that,QTL mapping of thirteen heterosis-related traits and male sterility traits in two-line flax hybrid were analyzed by using composite interval mapping(CIM).As a result,a total of seven QTLs related to plant height,branches per plant,yield per plant,linoleic acid and male sterility traits were detected in this study. |
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