Genetic Mapping Of QTLs Related To Heading Date On Wild Emmer Chromosome 7BS In Common Wheat Background

Wheat is one of the main food crops.Wheat heading date?HD?is an important agronomic trait,and closely related to the quality,yield,stress resistance and disease resistance.In some areas,it also affects the ecological and regional adaptability.Therefore,it is of great significance to study the regulatory mechanism of the genes associated with the HD at the molecular level for selecting fine wheat varieties with improved yield and quality.Chromosome arm substitution line?CASL?of wild emmer chromosome 7BS in the genetic background of the hexaploid common wheat variety Chinese Spring?CS?was used in this study and previous studies showed that the HD of CASL7BS was 6-8 days earlier than CS under normal sowing season?November?.In this study,CASL7BS and CS were used to study their response to photoperiod and verilization and to map the possible QTL loci on the chromosome arm 7BS of wild emmer using the F₂ separate population derived from the cross between them.The results were as follows:1.Under different sowing condition?in the greenhouse,field and growth chamber?,CASL7BS always had earlier HD than CS especially when they were planted under abnormal conditions such as greenhouse and growth chamber.2.The two parental materials?CASL7BS and CS?were planted under different temperature and light to test their reaction to vernalization and photoperiod.Consistent with the results of the above-mentioned field and growth chamber,when CASL7BS were treated for vernalization under long or short day conditions and then growing under short or long day conditions in the growth chamber,it also showed much earlier HD than CS.Epecially growing under short day?SD,8h light/16h dark?,its HD was about 49 days earlier than CS.When CASL7BS and CS were treated for vernalization under long day conditions and then growing under LD conditions?16h light/8h dark?,they were all earlier than the SD vernalization and growth in the SD conditions.For CS,a certain period of vernalization could promote the developmental process.But for CASL7BS,it was more important to grow in LD conditions,and the effect of vernalization on the HD is not very obvious.Especially without vernalization,CASL7BS was about 22 days earlier than CS.3.The observation of the differentiation process of immature inflorescence in CASL7BS and CS showed that CASL7BS is faster than CS in long or short photoperiod.All wheat materials under LD conditions were growing faster than those in SD conditions,indicating that LD can promote immature inflorescence differentiation.Under LD conditions,the immature inflorescence differentiation rate of CASL7BS and CS began to differ during single ridge stage,and they stayed for the longest time during double ridge stage.After the floret primordium,they could quickly complete differentiation.In SD conditions,they stayed longer time during elongating stage and single ridge stage,but shorter time during the double ridge stage than under the LD conditions.It revealed that vernalization can promote the emergence and reduction of the double ridge stage.4.F₂ plants derived from cross between CASL7BS and CS were planted in the field?November 12,2016,normal autumn sowing?and the growth chamber?February 13,2017,spring sowing?,forming two mapping populations?named as P1 and P2,respectively?to map the possible HD QTL loci on wild emmer chromosome 7BS.According to the HD distribution of P1,the early HD of CASL7BS was a quantitative trait controlled by multiple genes.The 26 pairs of polymorphic SSR markers were used to construct high-density genetic linkage map.The genetic maps of P1 and P2 populations span 85.18 cM and 58.69 cM,respectively,and the average distance between adjacent markers was 3.28 cM and 2.26cM.Using these two mapping populations,a QTL was detected consistently in a region of about 4.92cM flanked by C272 and C309 with LOD score of 5-8,explaining 10.14%and 12.35%of phenotype variation.According to above results,we concluded that the QTL loci on wild emmer chromosome 7BS is a new earliness per se?Eps?gene and designated as QEps-7BS.This study showed that CASL7BS was earlier than CS for many days under different sowing condition and light temperature conditions.The experiment of immature inflorescence differentiation also indicated that CASL7BS was faster than CS,and the double ridge stage was a critical period for immature inflorescence development.On these foundations,we map the HD QTL loci on chromosome7BS is a earliness per se?Eps?gene and designated as QEps-7BS,which laid the foundation for further fine mapping of the HD-related genes on the 7BS chromosome and revealing the molecular mechanism regulating the HD of wheat.