Evaluation Of Triticum Durum L. Germplasms And Its Utilization In Wheat Improvement

It is well known that the genetic diversity of cultivated wheat has been greatly eroded by modem breeding and planting modes. Narrow genetic basic not only limits the further improvement of yield and quality but also makes wheat increasingly vulnerable to biological and environmental stress. Therefore it is necessary to find and utilize the beneficial gene resource from the relative of cultivated wheat. Triticum durum L., with many useful genes for wheat improvement, is the secondary gene pool of bread wheat and easy to be utilized by hybridizing. Thus, it is important to evaluate the germplasm of durum wheat. In this paper, the population genetic diversity was estimated based on agronomic traits, SDS-/A-PAGE and EST-SSRs markers. In addition, threeα-gliadin genes from durum wheat were isolated and characterized. Furthermore, the durum wheat accession with high protein content was hybridized with cultivated wheat variety, and the cytological and agronomic characteristics of the F₂ and F₃ population were analyzed. The main results were described as following:1. The eight agronomic traits and grain protein content of 101 Triticum durum L. collected from eight countries and areas, were investigated based on analysis of variance, correlation, principal component and cluster. Higher variations of the eight agronomic traits were observed. The durum wheat investigated in this study have the beneficial traits of more tillers and spikelet per spike, and disadvantage of higher plant height, lower 1000-grain weight and longer growing periods. By clustering analysis, all the materials were divided into four groups, indicating that genetic distances based on agronomic traits were not associated with their geographic distribution. According to these main characters, tweenty-two accessions with one or some elite agronomic performances were screen out.2. The diversity of the storage proteins of 142 durum wheat accessions from 22 countries and areas was characterized by A-PAGE and SDS-PAGE. The higher gliadin genetic variation was observed by A-PAGE in the durum wheat. Furthermore, 142 accessions were divided into three major groups using the clustering analysis, indicating that the gliadin variations among durum wheat were associated with their geographic origin. A total of 14 HMW glutenin subunits alleles and 15 subunits combinations in T. durum L. studied. Tweenty accessions with subunits combinations being positive for quality were identified, which could be utilized in common wheat quality improvement. Meanwhile, two accessions were found to containing null subunits on Glu-A1 and Glu-B1, which was useful to characterize that how other endosperm protein than HMW-glutenin subunits effect the wheat quality.3. Using wheat EST-SSR markers, 60 durum wheat (Triticum durum L.) accessions from seven countries were investigated. Twenty-five primer pairs could amplify successfully in the 60 durum wheat accessions, of which tri-nucleotides repeats was dominant type. Higher numbers of alleles and PIC were identified on B genome than those on A genome. Mantel-test showed the genetic similarity coefficient matrix obtained from A genome markers was significant linear relative to that from B genome (P＜0.001), which suggested that the genetic differentiation among accessions reflected by two genomes was resemblant. Both Shannon's index and Gst (genotype/accession differentiation) indicated that the most significant differentiation had occurred in the durum wheat accessions from China. The analysis of molecular variations (AMOVA) showed that the significant eSSR differences existed both among the accessions within country and among countries, while the major proportion of variation was contributed by the differentiation among accessions within country. Compared to the other groups, the group of landraces from Ethiopia and Canada displayed the evident genetic uniqueness.4. Three coding sequences of gliadins genes, designed as Gli2_Dul, Gli2_Du2 and Gli2_Du3 with accession numbers in Genbank DQ296195, DQ296196 and DQ296197, respectively, were isolated from the genomic DNA of Triticum durum L. accessions CItr5083. Gli2_Dul and Gli2_Du2 encode the mature proteins with 314 and 287 amino acid residues, respectively. Gli2_Du3 is recognized as a pseudogene due to the stop codon occurring in the coding region. The amino acid sequences deduced from these gene sequences were characterized with the typical structure ofα-gliadin proteins, including the toxic sequences (PSQQQP). The peptide fraction PF(Y)PP(Q) is thought to be an extra unit of repetitive domain, slightly diverging from the previous report. Six cysteine residues were observed within two unique domains. Phylogenetic analysis showed Gli2_Du2 and Gli2_Du3 were closely related to the genes on chromosome 6A, whereas Gli2 Dul seems to be more homologous with the genes on chromosome 6B.5. The cytological and agronomic characteristics of the F₂ and F₃ population from Triticum aestivum×T. durum L. hybrids were analyzed. The mean of morphologic traits in F₂ population were adjacent to that of the low value parent. On average, F₂ hybrids had 36.54 chromosomes per plant. Based the chromosome number distribution, the male gametes with 19-21 chromosomes seemed to be superior to the rest, indicating the many individuals with all 42 chromosomes would appeare in F₃. The analysis for cytological and agronomic characteristics of F₃ plant line showed it was inadvisable to take the strategy of self-pollinated or backcrossing with hexaploid parent. Therefore the desirable individuals of hybrids population were backcrossed to other excellent bread wheat, which is very useful and efficient for the improvement of bread wheat by exploiting desirable genes in durum wheat.