| Common wheat is one of the most important staple food crops cultivated globally.The improvement of yield and quality,which includes industry and nutrition quality,are the most important breeding objectives.Yield and quality are severely affected by many factors,including heading date(HD)and preharvest sprouting(PHS),with seed dormancy as the major influencing factor.HD is an important trait determining crop adaptation to diverse environments and plays a vital role in wheat stability and yield potential.PHS is the precocious germination of grain before harvest leading to decreased grain yield and significant loss in the quality of grain and end-use product.The annual economic loss caused by PHS on wheat production has been estimated to be 1.2 billion US dollars worldwide.Ferulic acid(FA)is the most abundant bioactive compound in bread wheat and has demonstrated health-promoting effects.Producers and breeders have given wheat grains special attention due to their nutritional properties,antioxidant activities,free-radical scavenging abilities,skin care,antimicrobial and other therapeutic functions.A recombinant inbred line(RIL)population derived from a cross of Zhongmai 578(ZM578)/Jimai22(JM22),including 262 lines sown in multiple locations in three years,and a linkage map constructed by a wheat 50 K single nucleotide polymorphism(SNP)array,were used in this study,with the following objectives: 1)to identify quantitative trait loci(QTL)for HD,PHS resistance related seed dormancy(SD)and ferulic acid concentration(FAC),2)to develop breeder-friendly efficient kompetitive allele-specific PCR(KASP)markers for marker assisted-selection in breeding,3)to validate the KASP markers using a panel of the natural population,4)to identify putative genes of HD and FAC,and to discover their functions in other model plants.The main results are as follows:1.A high-density genetic linkage map of the ZM578/JM22 population was constructed from 1,507 bin markers on all 21 wheat chromosomes,spanning 2417.01 c M with an average distance of 1.59 c M per bin marker.The maximum number of markers was recorded in the A genome(562),followed by B(551)and D(394)genomes,respectively.In addition,SNPs were unevenly distributed among chromosomes,with 7B(155)and 7A(136)having the highest number,while chromosome 3D(7)and 6B(6)having the lowest number of SNP.2.The frequency distribution showed a normal distribution and continuous variation in the population for HD,germination index(GI),and FAC across environments,indicating transgressive segregation and the existence of polygenic inheritance of the traits.All the parameters were significantly influenced by the effects of genotype,environment,and genotype by environment interaction,with genotype contributing the largest.Significant and positive correlations were recorded for all traits among environments,with the value ranging from 0.38 to 0.89 for HD,0.52 to 0.76 for GI,and 0.54 to 0.75 for FAC,respectively.The broad-sense heritability among environments ranged from 0.60 to 0.93 for HD,0.91 to 0.98 for GI,and 0.87 to 0.95 for FAC.3.Nine QTL were identified for HD,explaining 2.0 to 28.6% of the phenotypic variations with LOD values ranging from 2.6-30.6.Five QTL were stable,including QHd.caas-3A,QHd.caas-4A,QHd.caas-5B,QHd.caas-7A,and QHd.caas-7D,with the positive allele of the former four contributed from JM22,whereas the last one coming from ZM578,respectively;The QTL located on chromosomes 4A and 7D did not correspond to any previously reported study,hence could be new.Six QTL for GI were detected for PHS resistance,explaining 3.0 – 8.02% of the phenotypic variance,with LOD values being of 2.5-7.1;QGI.caas-3A and QGI.caas-5A were stably detected in more than half of the environments tested with the resistant effect of QGI.caas-3A contributing by JM22,while the resistant effect of QGI.caas-3A contributing by ZM578.These two QTL did not correspond to any previously identified genetic loci for PHS-related traits,according to their locations in the Chinese Spring reference genome,indicating that they are likely to be new loci for PHS.Three stable QTL,including QFAC.caas-2D,QFAC.caas-3B,and QFAC.caas-4D were detected for FAC,explaining 3.2 – 8.0 of the phenotypic variance with LOD and additive effect values being of 2.1 – 4.1,with the positive allele coming from JM22,respectively.QFAC.caas-2D detected in all the five environments and BLUE,was likely to be a new QTL.4.Two KASP markers,K-AX-89466814 and K-AX-110766722,closely linked with the stable QTLs of QHd.caas-5B and QHd.caas-7D,were successfully developed and validated in a panel of 166 varieties.Four KASP markers,including K＿AX-109605367 and K＿AX-179559687 for QGI.caas-3A,and K＿AX-111258240 and K＿AX-109402944 for QGI.caas-5A,were developed and validated in a natural population of 100 varieties.The resistance alleles distribution was recorded as 82.7% at Qphs.caas-3A locus and57.1% at Qphs.caas-5A locus in the natural population.Three SNPs closely linked to QFAC.caas-2D,QFAC.caas-3B,and QFAC.caas-4D were successfully converted to KASP markers,and their effects were validated in a natural population of 110 varieties.All the above markers are useful to clear the way for marker-assisted selection(MAS)in wheat breeding.5.Candidate gene analysis revealed three putative genes involved in regulating flowering and other plant physiological processes,including Traes CS4A02G018800,Traes CS5B02G381200,and Traes CS7A02G111300 on chromosomes 4A,5B,and 7A,respectively.In addition,five putative genes relating to ferulic acid metabolism were detected on chromosomes 3B and 4D,including Traes CS3B02G1052800 LC,Traes CS3B02G041000,and Traes CS3B02G050300,Traes CS4D02G073600 and Traes CS4D02G074600.The result delivers valuable information for FAC-related gene identification involved in FA metabolism.It is necessary to validate the function of the candidate in the near future.These findings provide new QTL,genetic background,and tightly linked KASP markers for wheat improvement in HD,PHS resistance,and FAC for MAS. |
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