Mapping QTLs For Polyphenol Oxidase Activity In Common Wheat Grain

Common wheat (Triticum aestivum L.) is one of the most important and the oldest crops in the world. Steamed bread, noodle and dumplings are traditional basic food in our country, which are the production of wheat flour. The polyphenol oxidase (PPO) activity is a major factor to cause an undesirable brown discoloration of wheat based end products durning processing or storage. Hence, studing the activity of PPO in wheat and the location of its moleculer markers intensively is of great importance to the inhencement of the whiteness of wheat flour. In the present study, we report a new genetic linkage map developed from an F1-derived doubled haploid (DH) population of 168 lines, which was generated from the cross between two elite Chinese common wheat varieties Huapei 3 and Yumai57. The DH and parents were evaluated for PPO activity in three environments. QTL analyses were performed using the software of Icimapping 2.2 based on the mixed linear model approach. The primary goal of the study described here was to detect QTLs with additive effects for PPO activity. The results were as the following:1. A population of 168 DH lines was produced by anther culture from the cross between two Chinese common wheat varieties Huapei 3 (female parent)×Yumai 57 (male parent).Genetics analysis of quantitative traits were carried out by using the investigated results in three environments: normal irrigated and topdressed urea in 2009 (environment I), normal irrigated but no topdressed urea in 2009 (environment II), no irrigated but topdressed urea in 2009 (environment III). Analysis the variance of difference between the parental groups on PPO in the experiments showed significant difference among the PPO in DH population by SPSS, the test showed the trait approximately fit normal distributions. It was shown that the DH population can be used for the construction of the genetic map and QTL mapping.2. A genetic linkage map containing 324 SSR markers, using MAPMAKER/Expversion 3.0 software, was finally developed. The map covered a total length of 2141.7 cM with an average distance of 7.02 cM between adjacent markers in the map, which resulted in 24 linkage groups comprising 3 to 24 loci. Each of the linkage groups could be assigned to one of the 21 chromosomes based on the micro-satellite consensus map. This work found some large bins of cosegregating markers near the centromeric regions, which are known to have suppressed recombination. These unresolved regions may provide access to a high density of markers and thereby increase the chance of finding polymorphism among different germplasm materials. It will be interesting to see if the markers in the centromeric regions found in our study would be useful in detecting and tagging QTLs in further research. A further agreement between our work and similar studies is the observation of segregation distortion of certain markers.3. Based on the genetic map established from the DH population, the QTLs were detected using the software Icimapping 2.2 with the composite interval mapping of the mixture linear model. QTLs for PPO was analyzed in 1 croping seasons and 3 environments. A total of 13 QTLs were detected and distributed on 10 chromosomes 2A, 2D, 3D, 5A, 5B, 6A, 6B and 6D. Among them, 7 QTLs were major genes, while 6 additive QTLs were minor genes. The contribution rate of main effect gene qPPO-2D-2 is 65.84%, whose genetic distance from Xcfd168 is 0cM. The contribution rate of qPPO-2D-5 is 22.73%, whose genetic distance from Xcfd168 is 0cM. The contribution rate of qPPO-6D is 19.17%, whose genetic distance from Xgwm681 is 2cM. The contribution rate of main effect gene qPPO-2D-1 is 17.24%, whose genetic distance from Xcfd168 is 0cM. The contribution rate of qPPO-2D-2 is 65.84%, whose genetic distance from Xwmc170.2 is 0cM. The contribution rate of qPPO-5B is 13.47%, whose genetic distance from Xwmc160 is 0cM. The contribution rate of qPPO-2D-3 is 11.12%, whose genetic distance from Xwmc170.2 is 3cM.