| Wheat (Triticum aestivum L. em. Thell.) is one of the most important crops in the world. Due to repeated use of the same parental genotypes in modern breeding programs, genetic diversity in wheat cultivars has been increasingly narrowed, which limits further improvement of wheat against biotic and abiotic stresses. It is thus important to assess the genetic diversity in wheat germplasm for collection, conservation, and effective application of genetic resources and ultimately broadening genetic bases in wheat cultivar development. Landrace cultivars are promising sources of genetic variation. In China, 13,976 accessions of wheat landraces are currently maintained. However, the genetic diversity in Chinese wheat landraces is not well evaluated. Only a small proportion of the landraces were assessed for their morphological and agronomic traits. Modern molecular biological techniques are powerful to study genetic diversity of Chinese wheat landraces.In the present study, genetic diversity and heterogeneity among and within wheat landrace cultivars that originated from various wheat producing regions of China were assessed using microsatellite markers and high molecular weight glutenin subunits (HMW-GS). The genetic variations within the landrace cultivar Jiuquanjinbaoyin were evaluated for agronomic performance, gliadin composition and HMW-GS. This study was also conducted to determine genetic diversity and relationship among different accessions of Mazhamai and Daqingmang from various regions by means of A-PAGE, SDS-PAGE, and microsatelitte analyses. The following achievements were obtained.1. A set of 42 wheat microsatellite markers that were previously mapped onto each wheat chromosome arm were used for assessing genetic diversity of 81 wheat landraces from different wheat producing regions. Among the SSR markers analyzed, 95.2% were polymorphic, and two SSR markers were monomorphic. A total of 316 alleles were detected with an average of 7.5 alleles per locus. Polymorphic information content (PIC) for all accessions ranged from 0 to 0.90 with an average of 0.63. The average number of alleles of the SSR markers for the A genome (8.4) was greater than D genome (7.3) and B genome (6.5). The PIC value for the three genomes of wheat was comparable. The homoeologous group 7 chromosomes had the highest and the group 4 chromosomes had the lowest genetic diversity, respectively. The landrace cultivars from the Yellow and Huai River Valleys Facultative Wheat Zone and the Southwestern Autumn-Sown Spring Wheat Zone had the greatest genetic diversity, followed by Northern Winter Wheat Zone and Xinjiang Winter-Spring Wheat Zone. The landrace cultivars from Southern Autumn-Sown Spring Wheat Zone and Northeastern Spring Wheat Zone had the lowest genetic diversity. The genetic diversity of winter wheat landraces was higher than that of the spring wheat landraces. Clustering analysis generated by SSR analysis indicated that the genetic diversity of the landrace cultivars was not closely associated with their geographic regions of origin. However, the winter wheat or facultative wheat landrace cultivars were significantly different with the spring wheat landrace cultivars.2. The analysis of HMW-GS composition of 77 wheat landrace cultivars indicated that 26.0% of the landraces were heterogeneous within each cultivar, which had 2 to 6 glutenin phenotypes. A total of 16 glutenin alleles and 19 glutenin banding patterns were detected in Glu-A1, Glu-B1, and Glu-D1 loci, among which Glu-B1 and Glu-D1 loci had 7 alleles and Glu-A1 locus had only 2 alleles. New alleles, i.e., 7.1*+8, 7+8.1*, 1.5*+10, and 2+12*, and certain rare alleles, such as 7, 8, 5+12, 2+10, and 12, were detected. The highest frequency of heterogeneity was 80.0%, which was detected in the Northern Spring Wheat Zone. New alleles two at Glu-B1 and Glu-D1 were found. The composition of HMW-GS between different landrace cultivars showed different levels of heterogeneity, and the highest frequency of heterogeneity was 80.0%, which was detected in the Northern Spring Wheat Zone. The most variation was found in cultivars from the Yellow and Huai River Valleys Facultative Wheat Zone, the Middle and Low Yangtze Valleys Autumn-Sown Spring Wheat Zone, the Southwestern Autumn-Sown Spring Wheat Zone, and the Northern Spring Wheat Zone.3. Genetic heterogeneity within the landrace cultivar Jiuquanjinbaoyin was demonstrated by HMW-GS and gliadin composition. Identical glutenin and gliadin composition was observed in 10 seeds from a plant, but variation was detected among different plants. Totally, 6 HMW-GS patterns, which were formed by 7 glutenin subunits, were observed. The most variable locus occurred in Glu-D1 with 4 variants, and new subunits, i.e., 1.5*+10 and 2+12.2*, were detected at this locus. Gliadin analysis of 30 plants revealed 21 gliadin patterns, of which 8 belong toω-gliadin, 6 toγ-gliadin, 4 toβ-gliadin, and 3 toα-gliadin. The accession Jiuquqnjinbaoy examined in this study exhibited 10 gliadin genotypes.4. Mazhamai is one of the most distinctive landrace cultivar, which was used as a foundation parent in developing many outstanding improved cultivars. Genetic relationship of 8 Mazhamai accessions from various geographical regions were analyzed using 10 morphological and agronomical traits, composition of gliadins and HMW-GS, and 84 microsatellite markers. These homonymous accessions had high level of similarity in HMW-GS and 61.9% SSR loci analyzed. Heterogeneity within accession was detected in agronomic performance, gliadin composition, and certain SSR loci. The genetic variation of different accessions was associated with geographic regions of origin. Microsatellite analysis indicated that the highest variable was detected in chromosome 2A. However, chromosome 1A, 1D, 2D, 5B, and 7A did not show any variation in SSR alleles analyzed. The B genome was more variable than the A and the D genomes in terms of PIC value. Chromosomes in homoeologous group 2, 3, and 6 exhibited more genetic variation than other chromosomes.5. Genetic relationship among five accessions of the landrace cultivar Daqingmang that were collected from different sites of northeastern China was determined by analyses of agronomic performance, seed storage proteins, and 84 SSR markers. Identical agronomic traits were observed in these Daqingmang accessions. However, high level of variation was detected in gliadin composition, HMW-GS and 57.1% of the SSR markers. Heterogeneity in gliadin banding patterns, HMW-GS and some SSR loci was observed within each accession. Microsatellite analysis revealed that the highest variation was detected in chromosome 6A. Chromosome 1D did not show any variation in SSR alleles analyzed. The A genome was more variable than the B and D genomes. The highest variation was detected in homoeologous groups 4 and the lowest variation was detected in homoeologous group 1 and 7 as revealed by SSR analysis.
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