Genetic Control And QTL Mapping Of The Branched Spike In Wheat

Wheat (Triticum aestivum L.) is one of the most important crops in China.Wheat production directly affects the development of national economy. Branchedhead is a variation type of spike in common wheat, which has a number of spike onthe main rachis. Branched head wheat produces increased number of kernels by themultiple spikelets on the rachilla. Study on branched head not only facilitatesunderstanding the development of wheat spike, but also has potential in yield increaseof wheat. In this study, a DH population derived from the cross between Linzhangmaiwith branched head and Thatcher with normal head was used to conduct geneticanalysis on plant height, spike length, spikelet number per spike, number of rachis,kernel numbers per spike, and thousand-kernel-weight and map QTLs for branchedhead trait in Linzhangmai by SSR markers.Genetics analysis of quantitative traits was carried out using the results obtainedin Beijing and Handan, Hebei Province. Analysis the variance demonstrated thatsignificant difference was observed in the plant height, spike length, number ofspikelet per spike, number of nodes on rachis, kernel number per spike, andthousand-kernel weight. Analysis the frequency distribution of each phenotype trait inDH population by SAS indicated that all the traits fit a normal distribution except forspikelet number per spike, demonstrating that plant height, spike length, number ofnodes on rachis, kernel number per spike, and thousand-kernel weight were inheritedin a quantitative mode and spikelet number per spike was inherited as a qualitativetrait. Results of correlation analysis showed that the branching index wassignificantly correlated with spikelet number per spike and kernel number per spike.This result provides evidence that branched head has an significant impact on theyield component traits in wheat.In this study,97pairs of SSR microsatellite primer on chromosome2A wereused in detection of QTLs that are responsible for the branched head trait in Linzhangmai. Fifty-five primer pairs exhibited polymorphism between the twoparents Linzhangmai and Thatcher. Twenty of them displayed polymorphism betweenthe DNA bulks from branched head plants and normal head plants, which were usedto genotype the223DH lines. We found two QTLs controlling the branch index inchromosome2A, QBi1and QBi2. The additive effect of these two points were fromlinzhang wheat and were stable expressed in the two years in Handan and Beijing.QBi1was a stable QTL, could explain the19.4-23.0%of the Phenotypic variation.Howereve QBi2with small effect with the Phenotypic variation. QBi1and QBi2contrled the spikelet number per spike and stable expressed in all four environmentalconditions. The confidence interval of QBi1was approximately10cM. Themolecular markers wmc296and wms122on the side of QBi1could be used ascandidate markers for marker-assisted selection for the branch index and the spikeletnumber per spike. The confidence interval of QBi2was big, the flanking markers ofQBi2may be less effectivse for marker-assisted selection. Given the relatively smalldensity of molecular markers, the greater QTL confidence interval, we need encryptmarkers on the two sites, especially QBi1.