Genetic Analysis Of Diversity And Root Drought Traits At Germination Stage In Derivative Offspring Of Mazhamai And Xiaobaimai Wheat (Triticum Aestivum L.)

In recent years,with the global warming,the drought has become more and more serious,which has seriously restricted the development of wheat production.Breeding drought-resistant and water-saving wheat varieties is one of the effective approaches to cope with the climate change.As the initial stage of wheat life cycle,the drought resistance at germination stage is one of the decisive factors for ensuring emergence,seedling quality,and grain yield.The root system is the primary organ in response to soil drought stress,and a good root architecture can improve the drought resistance of wheat.Therefore,the identification of drought resistance and root-related traits of wheat germplasm at germination stage can provide a theoretical basis for wheat improvement.In this study,Mazhamai,a landrace from the Huanghuai Winter Wheat Zone,and Xiaobaimai,a landrace from the Northern Winter Wheat Zone and their derivatives were used as the plant maerials.The genetic diversity and root traits were analyzed,and the drought resistance index and evaluation method were screened.A genome-wide association analysis between the 660 K SNP markers and phenotypic traits was carried out to explore significant SNP loci in root-related traits.The main findings are as follows:1.Genetic diversity analysis showed that the number of polymorphic SNP markers in three wheat genomes was B>A>D.The number of polymorphic markers in the fourth homoeologous group was the least.The genetic diversity of 149 tested materials(H)was ranged from 0.095 to 0.500,with an average of 0.336.The nucleotide diversity index(?)was ranged from 0.272 to 0.435,with an average of 0.340;and the genetic similarity coefficient(GS)varied from 0.335 to 0.997 with an average of 0.619.Cluster analysis indicated that the Mazhamai and Xiaobaimai were closely clustered in subgroup I,and their derived varieties(lines)were divided into five subgroups,of which the single derivative varieties(lines)of Mazhamai or Xiaobaimai before 2000 were mainly clustered in the subgroups I,II and III,and the most varieties(lines)with both Mazhamai and Xiaobaimai consanguinity released after 2000 were divided into subgroups IV and V.2.Under drought and well-watered conditions,except for the root number which did not reach a significant difference level,the all other traits reached a highly significant difference level.Correlation analysis showed that there were different degrees of correlation between the drought resistance coefficients of each root indicator.The comprehensive evaluation indicators were all significantly correlated with total root length,root surface area,root volume,shoot fresh weight,root fresh weight and total biomass,and all correlation coefficients were more than 0.64.Using comprehensive drought resistance coefficient,comprehensive drought resistance index and comprehensive membership function drought resistance evaluation method,11 strong drought resistant germplasm and 17 sensitive germplasm were screened out from the 146 accessions.3.SNP markers were used to analyze the genome-wide association of root traits at germination stage.A total of 34 peak SNP loci were detected with pleiotropic effects.Functional annotation results showed that the homologous gene MED12 of the Traes CS5A02G532500 candidate gene can activate primary root cell division and elongation,as well as auxin response,thereby regulating the root architecture.The expression paterns showed that Traes CS2A02G577600,Traes CS3A02G507600 and Traes CS5A02G532000 candidate genes had different degree expression under PEG-6000 stress,indicating that these three kinds of candidate genes may be related to drought resistance,providing information for mining related genes.