Fine Mapping Of Drought Resistance Analysis Of Main Effect QTL Controlling Seedling Lateral Root Number On The D Genome Of Wheat(Triticum Aestivum L.)

Wheat(Triticum aestivum L.,AABBDD)is a typical allohexaploid crop,which is most widely cultivated in the world.During the formation and domestication of allohexaploid wheat,many excellent genes in the ancestral species of Aegilops tauschii.have not been discovered due to the limited number of genotypes involved in the origin of hexaploid wheat D genome.Drought is the main stress factor limiting crop productivity,improving root water absorption capacity is an effective way to improve crop drought resistance,and lateral roots,as an important part of wheat root water absorption,play an important role in adapting to drought stress environment.A major QTL(QLrn.qau-5D)was detected on chromosome 5D using a recombinant inbred line derived from a common hexaploid wheat variety with similar A and B genomes but significantly different D genomes(TAA10)and the resynthesis of hexaploid wheat(XX329),it could explain8.4% variation of lateral root number.On this basis,fine mapping of dominant QLrn.qau-5D and its relationship with drought resistance was studied by using residual heterozygous lines and near isogenic lines(NILs),which laid a foundation for analyzing the regulation of D genome on lateral root traits and the biological function of map-based cloning related genes.The main results are as follows:1.In order to precisely locate QLrn.qau-5D,polymorphic molecular markers were designed and screened using genome resequencing information of parents TAA10 and XX329,and then the QLrn.qau-5D loci interval is marked and encrypted.A genetic map containing nine polymorphic molecular markers was constructed with a genetic distance of 135.5 c M.On the basis,QLrn.qau-5D was further confirmed by relocalization of the QLrn.qau-5D locus using the encrypted genetic map,explained 8.4% variation of lateral root number,and the enhanced allele of QTL for lateral root number at seedling stage was derived from TAA10.From the backcross population and the secondary isolation population derived from the remaining heterozygous lines(1 006 plants),52 exchange plants were screened.Shrinking the QLrn.qau-5D interval to a physical distance of 3.1 Mb between the markers QAU-8 and QAU-10,and its interval contained 47 high confidence genes.On the basis of fine mapping,the In Del molecular marker 5D48 closely linked to QLrn.qau-5D was used for genotyping of Aegilops tauschii and common wheat.The results showed that 1086 samples of common hexaploid wheat and 35 samples of Aegilops tauschii had the same allele type with TAA10 genotype,and only 38 samples of Aegilops tauschii had the same allele type with XX329 genotype,suggesting that 5D48 in XX329 was a specific allele type from Aegilops tauschii.2.In order to investigate the relationship between QLrn.qau-5D locus and drought resistance,a group of near isogenic lines(5D+/5D-)containing the QLrn.qau-5D interval with the smallest physical distance were used as materials for drought stress.With the extension of drought stress time,near isogenic line(5D+/5D-)showed wilting from booting stage to anthesis stage,but the degree of wilting in near isogenic line 5D+was less than that in near isogenic line 5D-.After drought stress,physiological and biochemical indexes of near isogenic line at anthesis stage were measured.Under drought stress,the water loss rate of near isogenic line 5D+ was lower than that of near-isogenic line 5D-,and its antioxidant enzyme activity,osmotic regulatory substance accumulation and chlorophyll content were higher than near isogenic line 5D-,MDA content and relative electrical conductivity were lower than near isogenic line 5D-.Agronomic traits of near-isogenic lines under drought stress were measured at the later grain filling stage and after harvest,compared with near isogenic line 5D-,near isogenic line 5D+ had thousand grain weight,tiller number,yield per plant.These datas suggest that near isogenic line 5D+ was more drought resistance than near isogenic lines QLrn.qau-5D,which controls the number of lateral roots at seedling stage,is associated with drought resistance of wheat,and could improve the yield and drought resistance of wheat.