Analysis Of Genetic Characteristics Of Melon Seed Trait

Seed-related traits are significant agronomic traits,which are one of the critical factors impact crop output and a considerable part of seed quality trial.It is of great meaning to illustrate the genetic amelioration machinery of melon seed traits in the cause of breeding tough seedlings,crop genetics and breeding,variety selection and improvement of economic benefits.In this study,12 melon lines were used as parents,of which 2 were female parents（P5 and No.416）and 10 were male parents（BL-1,NO.1496,P10,ZL001,BH-5,YL020,GL-5,ZQ002,DM-68 and YH-7）.According to the NC-Ⅱincomplete diallel crossing method,20 combinations were allocated,and the combining ability and heritability of three seed traits in melon were analyzed by using the DPS data processing system.The best female parent P5,best male parent P10 and best combination P5×P10 was selected by combining ability and heritability analysis,which was used to construct the F₂segregated population and F_2:3families.A total of 450 F₂generation plants were used for genetic analysis of seed-related traits.127 F₂generation plants were sequenced for SLAF-seq and construct a highly saturated melon genetic map.QTL analysis of seed-related characters was carried out.The results are as follows:1.The results of GCA analysis of 12 parents are as follows:GCA effect of female parents.P5 was higher than that of female parent No.416 in 100-grain weight,so P5was the best female parent in 100-grain weight,and the effect value of No.416 in seed length was greater than that of P5 in seed length and No.416 in seed width.In terms of the size of GCA effect,the advantage and disadvantages of 3 characters of 10 male parents were ranked as follows:P10>BH-5>GL-5>BL-1=NO.1496>YL020>ZL001=ZQ002=YH-7>147.It shows that P10 is the best male parent.2.The results of SCA analysis of 20 cross combinations showed that 10,8 and 12combinations had positive effects on 100-seed weight,seed length and seed width,respectively,among which the combination P5×No.416 had the highest effect on seed length,followed by P5×P10,and the combination P5×P10 had the highest effect on100-seed weight and seed width,indicating that the combination had the best performance in 100-seed weight and width.Based on the above performance,the P5×P10 combination was selected as the best combination for seed size selection.3.The results of heritability analysis of 20 hybrid combinations showed that the broad and narrow heritability of 100-seed weight of melon seeds were 93%.The results indicate that genetic variation mainly prompted the discrepancies in the midst of F₁combinations,and the environment had little effect on the difference.100-seed weight can be used as an index for the pick of parents,which is fit in with the analysis of its combining ability.4.A high density genetic linkage map of melon was constructed by SLAF-seq,which contained 12 linkage groups with a total length of 1356.49 c M and an average genetic distance between markers of 0.37 c M.Genetic analysis of seed-related traits was carried out in the F₂segregation population of P5×P10 and F_2:3families.The results indicate that seed length,seed width and 100-seed weight showed normal distribution,which were quantitative traits.Using F₂population and F_2:3families to map QTL controlling seed related traits,10 QTL were obtained,of which 5 QTL were related to 100 seed weight.2020-hsw6.1 was located between 1,082,887 and 1,206,028 on melon chromosome 6,LOD value was 2.65,which explained 13.97%phenotypic variation.2020-hsw7.1 is located between 458 518 and 1 212 963 on chromosome 7 of melon,LOD is 2.81,which explains 9.76%of phenotypic variation.2021-hsw3.1 is located between 31 447562 and 31 470 545 on chromosome 3 of melon,LOD is 12.69,which explains 36.55%of phenotypic variation.2021-hsw5.1 is located between 3 355 789 and 3 537 407 on chromosome 5 of melon,LOD value is 7.15,which explains 8.70%phenotypic variation;2021-hsw7.1 is located between 412 326 and 2 601 463 on chromosome 7 of melon,LOD value is 2.90,explaining 1.63%phenotypic variation.Two QTL were related to seed length,2020-sl3.1 was located between 31 430 517 and 31 553 644 on chromosome 3 of melon,LOD value was 8.31,which explained 27.43%phenotypic variation;2021-sl3.1 located between 31 430 517 and 31 659 961 on melon chromosome 3,LOD value was 13.82,explained 43.73%phenotypic variation.Three QTL were correlated with seed width（2020-sw3.1,2020-sw12.1 and 2021-sw3.1）.2020-sw3.1 was located between 31 447 562 and 31 470 545 on chromosome 3 of melon,and the LOD value was 3.37,which explained 16.03%phenotypic variation.2020-sw12.1 was located between 1 254 239 and 1 313 909 on melon chromosome 12,LOD value was 3.38,which explained 12.88%phenotypic variation.2021-sw3.1 is located between 31 430 517 and 31 659 961 on chromosome 3 of melon,and the LOD value is 10.00,which explains 41.25%phenotypic variation.5.According to the preliminary consequence of SLAF-QTL analysis,a total of 10QTL associated with 100 seed weight,seed length and seed width were identified,of which 5 QTL were located in the same interval of chromosome 3 from 31 430 517 to31 659 961,which contained 0.23Mb and 34 candidate genes.CAPS markers were used to further map melon seed related traits in 92 F_2:3families in the candidate interval.Three QTL,sl3.2,sw3.2 and hsw3.2 related to seed length,seed width and 100seed weight were all located between chromosome 3 and chromosome 31 458 160 to 31463 441,respectively.The interval contained 5.28 kb.There are two candidate genes with LOD values of 46.04,37.85 and 28.77,additive effects of-1.69,-0.72 and-0.62,and contribution rates of 88.53%,83.71%and 75.37%,respectively.