Analysis Of QTLs For Grain Size And Yield Traits Using A Mutant Line Of High Grain Weight In Wheat

The traditional method of chemical mutagenesis can produce high-density induced mutations with similar genetic background. This can not only solve the problem of poor germplasm in wheat breeding, but also provides a research platform for the fine positioning, cloning, and functional analysis of related genes. A high grain weight mutant line M8008 with increased plant height was identified from a library of mutants of the common wheat cultivar YN15 induced by ethylmethane sulphonate (EMS). In this study, F2 populations and the derived F2:3 progeny were produced from crosses of'M8008×YN15'(MY population) and'M8008×Shijiazhuang 54 (SJZ54)'(MS population). These were used for construction of genetic linkage map and QTL detection.(1) Compared to the wild type YN15, variances of M8008 were significant with a 10 g increase of TGW and 9 cm increase of PH. Variances of the yield trait such as SL and FSS and grain size trait such as GL and GW were significant at the same time. Transgressive segregations were observed for all investigated traits. All traits exhibited continuous distribution, indicating a quantitative nature of inheritance.(2) Most simple correlation coefficients (r) were significant. All r-values were significant between yield traits (PH, SN, SL, FSS, and GN) except for r-values of PH-GN in the F2:3 of MY and SL-GN in F2:3 of MS. All r-values were significant between grain size traits (GL, GW, GLW, FFD, and TGW), except for r-values of FFD-GL/GW/GLW in the F2:3 of MY and GLW-GL in the F2 of MY and MS. Most r-values between yield traits and grain size traits were significant.(3) A total of 1069 SSR and EST-SSR markers were used to detect polymorphisms between M8008 and YN15. Of these, 222 markers (20.8%) showed polymorphisms. The polymorphic markers were distributed on all 21 wheat chromosomes. The polymorphic SSR fragments between M8008 and YN15 were of two types: presence or absence of the band (Type 1), 14 polymorphic markers (41.2%) on chromosome 2D belong to this type; different length of the band (Type 2), the other 20 polymorphic markers (58.8%) on 2D belong to this type. The polymorphism of type 2 suggested that other mechanisms of EMS mutagenesis (non-transition of G/C-to-A/T) are very important.(4) Twenty-four markers were detected as the same polymorphism between the parents and the PSG, and these markers were used to scanning the F2 of MY population. Of which, the marker wmc41 on chromosome 2D was related to TGW, GW and FFD, while markers of wmc426 and wmc76 on 7B were related to PH by correlation analysis. Thus, we used the markers on chromosome 2D to detect polymorphisms in the F2 generation. After screening the two F2 populations using the polymorphic markers, linkage maps of 2D were constructed with a total genetic distance of 115.2 cM for MY and 250.4 cM for MS. The map derived from the MY population was generally in keeping with that from MS population. 6 polymophic markers on 7B were were used for map construction of 7B.(5) Seven QTLs for grain size traits were identified in F2:3 of MY on chromosome 2D and 7B, while 4 QTLs for grain size traits were identified in F2 and F2:3 of MS on chromosome 2D. QTLs for grain size (QGw,QGlw,QFfd and QTgw) in MY and MS formed one QTL cluster in each population on chromosome 2D, which in MY covered the marker wmc41 and in MS was near wmc41. There was also a QTL cluster for yield trait (PH, SL and SN) detected in MS on 2D. A QTL for plant height in the F2:3 of MY was detected between Xwmc76 and Xwmc426 on chromosome 7B, with a contribution of 9.33%. There was a QTL cluster for grain size trait (TGW, GW and FFD) on 7B.(6) Surprisingly, the addictive effects of QTLs for GW and TGW were negative, indicating that the effects of the QTLs were decreased in M8008, though the phenotypes of GW and TGW of M8008 were higher than of either parent (YN15 or SJZ54). In other words, the QTLs had increased effects in smaller size cultivars YN15 and SJZ54.