Genetic Mapping Of QTLs Related To Heading Date On Wheat Chromosome2BS And Identification Of Their Candidate Gene

Heading date is an important agronomic trait regulated by several genetic factors. A set ofcommon wheat (Chinese Spring, CS)-wild emmer [Triticum turgidum L. subsp. dicoccoides (TDIC)]chromosome arm substitution lines (CASLs) was used to examine the heading date and locate therelative QTLs conferring later or earlier earing.The genetic loci accelerating earing were located on TDIC chromosome arms3A and7BSrespectively, those for delaying heading were located on4AL and2BS. To map the QTLs conferringto later earing on2BS, F2segregation populations derived from two cross combinations involvingCASL2BS as one parent were developed, including CASL2BS×CS (later heading x parent) andCASL3AL x CASL2BS (earlier heading x later heading), and all of them were planted in twodifferent times. The heading date varied considerably among individuals of these four conditions. Agenetic map on2BS consisting of12SSR markers and one SSCP marker was constructed by usingthese F2populations, spanning a genetic length of58.9cM with an average marker density of4.5cM,on the genetic map Ppd-B1in21.5cM. Ppd-B1, a photoperiod-sensitive gene, was mapped onchromosome arm2BS as a SSCP molecular marker and validated to be tightly linked to the majorQTL associated with later earing of CASL2BS, explainning high ratio of phenotype variation in thesefour conditions (i.e.57.24,76.72,23.64and29.31%respectively) at the significance (P<0.05) LODthreshold of3.0. Ppd-B1gene were mapped among the Xwmc25-Xgwm410, and have the greatestsatisfaction to QTL mapping. That means Ppd-B1may be the key gene leading to the heading-later ofCASL2BS, and may be the candidate gene of later heading.Additionally, an interaction of the Ppd-B1gene with QTLs on3AL was also validated. Analysisof the amino acid sequences of Ppd-B1gene between CS and TDIC, one amino acid mutations in thedomain of Ppd-B1gene were detected, implying that the mutations of amino acid in the domain ofPpd-B1gene might be the reason for the variation of heading date between CASL2BS and CS.