Evaluation To The Utility Of Molecular Markers For Important Genes In Wheat

In recent years, a large number of genes and QTLs related to disease resistance, quality, development and other traits have been mapped in wheat genome. Despite the widespread use of molecular markers in wheat improvement has been report; we have not yet seen their impact on wheat breeding through varieties release for several reasons. Firstly, the molecular markers for MAS in wheat are effective or not? Secondly. How to improve the efficiency of MAS in wheat breeding? Accordingly, the objective of the current study was to evaluate the utility of101molecular markers in MAS, and identify the genetic and phenotypic characteristics of136Chinese wheat varieties, then compare the correlation of some genes and phenotypes. At last, we investigated the different selection strategies and consideration of when to screen, what proportion to retain and the impacts of domaint vs.codominant marker. The mainly progresses were showed as follows:1. There are significance differences in the utility of101molecular markers for MAS. According to the utility, the101markers can be classified into three types:51markers, accounting for50.5%of the total markers, can be directly used in MAS, such as Pm21D/Pm21E and WE173F/WE173R.22markers, accounting for27.2%, can be used as reference marker in MAS, such as Xcfd81-5DF/Xcfd81-5DR and Pm4a/bF/Pm4a/bR. The effects of such markers can be further evaluated through hybridization between the control carrying target gene and other varieties with different genetic backgrounds.28markers, accounting for21.8%, can not be used in MAS, such as Whs3501F/Whs350R and Whs3501F/Whs350. More closely linked markers to the target gene or QTL should be identified in future.2. Some excellent genes should be transferred into Chinese major varieties as soon as possible. The Results indicated that lB/lR and Pm8is still high portion; dominate with frequencies of73.5%and47.8%, respectively. Some excellent genes and QTLs, which have a positive effect on quality and disease resistance, have not yet been fully utilized in wheat breeding. These genes include14+15,17+18, QPhs.ocs.3A-l, Wx-Alb, Wx-Dlb, Pm4, Pm6, Pm12, Pm13, Pm17, Pm21, Pm24, Yr26, Lr34/Yrl8, Lr24-Sr24, and so on. Four alleles related to development traits, including Vrn-Dl.Rht-Blb, Rht-Dlb and Rht8, are widely distributed, accounting for34.6%,36.8%,44.1%and22.8%. Interestingly, the dwarfing allele Rht-Blb was not detected in Northern China Plain Winter Wheat Region. The photoperiod sensitive allele Ppd-Dlb was only detected in the spring varieties Kehan16and Kehan21, all other genotypes carried the photoperiod insensitive allele Ppd-Dla. It is very important to transfer above disease resistance, high-quality genes into Chinese major varieties as soon as possible.3. The phenotypes of varieties are controlled by not only gene function but also gene composition and gene interaction. The results indicated that the composition of vernalization genes is closely related to cold tolerance of varieties. Varieties with Vrn-Al and Vrn-Bl alleles are always poor low-temperature tolerance. Only few varieties with excellent abiotic stress tolerance, although with Vrn-Al or Vrn-Dl alleles, are still good cold-tolerance. The wheat varieties mainly contain four types of semi-dwarfing alleles:Rht-Blb, Rht-Dlb, and Rht-Blb+Rht8, and Rht-Dlb+Rht8genes. The effect of RhtDlb and RhtBlb on plant height reduction is obviously higher than Rht8. Additionally, plant height reduction improves kernel weight, while resulting in reduce number of grains per spike. Under the background of RhtBlb or RhtDlb, the plant height of varieties was not significantly affected by Rht8. Varieties carry with RhtDlb and RhtBlb, lead to reduce not only kernel weight but also number of grains per spike.The quality attributes is mainly determined by the composition and proportion of quality-related genes, not few "excellent" genes. To varieties with special glutein attributes, the high molecular mass glutenin subunits5+10had no obvious effect on the quality improvement. While the1BL/1RS translocation caused a significant decrease in technological properties of bread wheat. Elimination of the high molecular mass glutenin subunits and Pinb-Dlb alleles can be used as selection criterion for soft wheat breeding. In addition to Pm21, no certain rules can be found between other resistance genes and phenotypes. Therefore, the susceptible parents, both identified by phenotypic and genotypic selection, should not be used in disease resistance breeding.4. A reasonable strategy of MAS selection in gene transfer and gene pyramiding was proposed. The results indicated that the probability of F2generation containing the target gene about20%to60%, when dormant gene was detected by dominant marker, or recessive gene was detected by codominant marker. Using dominant markers to detect recessive genes, the probability of F2generation containing the target gene about10%to30%. Therefore, Co-dominant markers can be more efficiency than dominant markers for the detection of recessive genes. The probability of selection to the target gene in F3generation was significantly lower than the F2generation. The choice of the target gene should be carried out in the early generation as soon as possible. The efficiency of marker assisted gene pyramiding is closely related to the types of target gene and molecular marker. The probability of pyramiding three genes was significantly lower than that of two genes. As a result, pyramiding two genes should be preferred in wheat molecular breeding.