| Wheat genetic resources are the foundational materials for wheat breeding. They are also the basic materials for study the origin, evolution and classification, ecology, physiology and biochemistry of wheat.Studies on wheat genetic diversity can provide theoretical foundation for some research, including the sampling of genetic resources, classifying between species and varieties, evolution, and establishment of core collection. Establishment of core collection is helpful for research, exchange, utilization and management of wheat genetic resources. Therefore, genetic diversity and core collection are the key and core contents for study wheat genetic resource. Genetic diversity of all modern varieties in Chinese wheat candidate core collection and core collection in Northwestern Spring Wheat Region were studied by fluorescence detection system of Microsatellite markers in this paper. Through these research, genetic diversity level and distribution characteristic, genetic diversity tendency in modern varieties during the past five decades for Chinese wheat genetic resources would be more clear. At the same time, a good quality core collection that representing more than 70% genetic diversity with 3% accessions was finished successfully, all which will provide important academic bases and material foundations to genetic research and breeding practice of wheat. Major results are described as the following:1. 451 wheat varieties from Northern Winter Wheat Region were analyzed by fluorescence and silver-staining detection systems of microsatellite markers. After amplifying with 24 pairs of SSR primers, total 235 alleles were obtained and average of 9.8 alleles ranging from 3 to 20 were detected at each locus with silver-staining detection system. However, with fluorescence detection system total 312 alleles were obtained and average of 13 alleles ranging from 4 to 24 were detected at each locus. There are average of 3 more alleles detected by fluorescent system than silver-staining at one locus. In addition, With almost equal cost, the efficiency of fluorescent system is 7.8 times than that of silver staining system without consideration of instrument investment. Therefore, low use cost, high throughput and robotization in fluorescence detection system of microsatellite markers make large-scale genome scanning and genotype analysis possible.2. From different genomes, homoeologous, chromosomes, and different regions, genetic diversity of 1586 modern varieties in Chinese candidate core collection was analyzed by fluorescence detection system of microsatellite markers. In the molecular level, genetic diversity change tendency in Chinese modern varieties during the past five decades was evaluated further.2.1 All accessions were amplified by 74 SSR primers, total 1336 alleles were detected, among which 1253 alleles could be located into 71 loci. For these 71 loci, the range of allelic variation was 4 to 44 with average of 17.6, and its PIC value was 0.19 to 0.89 with average of 0.69.2.2 In the three genomes of wheat, the average genetic richness was B＞A＞D, and the genetic diversity indexes was B＞D＞A. Combining these results, selection pressure of wheat breeding to A genome was the largest in China, so its diversity decreased obviously.2.3 Comparing of genetic diversity among 7 homoeologous, the average genetic richness was 2=7＞3＞4＞6＞5＞1, and the genetic diversity indexes was 7＞3＞2＞4＞6＞5＞1. In total, the homoeologous group 7 possessed the highest genetic diversity, while the homoeologous group 1 was the lowest. For all homoeologous, the homoeologous group 5 took great change in genetic diversity.2.4 Studies on genetic diversity of 21 wheat chromosomes, the average genetic richness was 3B＞2D＞5B＞7A＞7B＞2B=1A＞6B＞4B＞7D＞5A＞6A＞4A＞3A＞1B＞3D＞2A＞1D＞6D＞5D＞4D, and the genetic diversity indexes was 2D＞6D=3B＞7D＞7B＞3A＞7A＞3D＞4A＞2B＞5B＞4B＞2A＞5A＞1A＞1B＞6A＞4D＞6B＞1D＞5D. Obviously, 7A, 3B and 2D possessed much higher genetic diversity, while 2A, 1B and 4D were the low...
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