SNP-Based Association Analysis For Seedling Traits And Genetic Variation In Durum Wheat Accessions(Triticum Turgidum L.ssp.durum Desf)

Wheat(Triticum spp.)is one of the major cereal crops grown throughout the world.Durum wheat(Triticum durum Desf.)is extensively cultivated in the medium to low-precipitation areas of the Mediterranean.Seedling characteristics and best stand establishment are essential in the production of cultivated wheat.The sustainable development of wheat cultivars could be through the conventional breeding and with relevant biotechnology.Association mapping tool has been used to study the genetic basis of complex traits in several plants to identify candidate genes.Single nucleotide polymorphisms(SNPs)perform polymorphisms between wheat cultivars could provide an unprecedented resource for wheat diversity analysis and hence are very valuable.The aim of this study was to discover chromosome regions and the anchoring SNP markers associated with seedling traits in durum wheat and to assess,evaluates genetic variability and characters associations of durum wheat genotypes based on phenotypic morphological seedling and agronomic traits.The main results were summarized as follows:1.SNP-based association analysis for seedling traits in durum wheat(Triticum turgidum L.durum(Desf.))Association analysis is an effective approach to understanding the relationship between phenotypic variation and genetic polymorphisms.In the present study,150 accessions of worldwide originated durum wheat germplasm(Triticum turgidum spp.durum)were observed for major seedling traits and their growth.Root length,number of main roots,seedling height,number of leaf,leaf area,fresh weight,growth rate of the traits,and growth gain of the traits were evaluated under controlled conditions of hydroponics at the 13 th,20th,27 th and 34 th day after germination.The chlorophyll content and biomass traits,including root dry weight,shoot dry weight,and total seedling dry weight were measured at the 34 th day after germination.ANOVA analysis was performed for each of the seedling traits.Correlation analysis was conducted among the seedling traits and three field traits at maturity,plant height,grain weight and 1000-grain weight observed in four consecutive years.Associations of the measured seedling traits and SNP markers were analyzed based on the mixed linear model(MLM).The results indicated that highly significant genetic variation and robust heritability were found for each seedling trait.Many significant correlations existed among the seedling traits,and between the seedling and field mature traits.In total,763 significant associations were detected for all the traits and four growth stages.Some(140)SNP markers associated with multiple traits,indicating non-neglectable pleiotropy in the seedling stage of durum wheat.The associations nonrandomly distributed across the durum wheat genome,with the higher number in the B than the A genome,and in the 6,1 and 7 chromosomes.The associated SNP markers could be helpful for genetic analysis of seedling traits,and breeding of new wheat varieties with strong seedling vigor.2.Genetic Variability and Heritability Estimates for Yield and Yield Components in Durum Wheat Accessions(Triticum turgidum L.ssp.durum Desf)A field experiment was conducted to evaluate 150 accessions of worldwide originated durum wheat(Triticum turgidum L.spp.durum)grown for four consecutive cropping seasons.The objective of the study was to assess the genetic variability in genotypes of durum wheat using phenotypic agronomic traits.The genotypes were grown in a randomized complete block design with three replications and evaluated for ten traits.The highest genotypic coefficients of variation and genetic gain were observed for rachis internode length of main spike(cm)in four seasons.Plant height,rachis internode length of main spike,length of main spike,panicle neck length of the main spike followed by the number of spikelets on main spike had the highest heritability estimate(above 87%)during these seasons.High genetic advance was reported for the grain number per plant and plant height in four years.Highly significant differences among genotypes were revealed for all traits.Grain yield per plant showed a high degree of positive association with the grain number per plant(r = 0.86),number of effective spikes(r = 0.59),panicle neck length of main spike(r = 0.59),number of spikelets per plant(r = 0.53),1000-grain weight(r = 0.51),rachis internode length of main spike(r = 0.35)and number of spikelets on main spike(r = 0.27).1000-grain weight showed significant negative association with the number of spikelets per plant(r =-0.22).Phenotypic path analysis revealed that grain number per plant(0.868)and 1000-grain weight(0.495)had direct contribution as regards grain yield.Therefore,these traits would be considered as selection criteria for yield improvement in wheat.The study revealed that there is an abundant genetic variability that can be exploited for use in breeding activities in wheat crop.