| Chestnut (Castanea mollissima Blume) is an ancient deciduous fruit tree crop in the temperate zones, which originates in China. Because of diversity of ecological inhabits and differences and selections of adaptability between chestnut for ecological environments, and a long selection by natural factors, chestnut trees evolutes and forms different geo-ecological groups under different geo-ecological conditions: the Yangtze group, the Northern China Group, the Northwest Group, the Southwest Group and the Southeast group. The diversity of 3 wild chestnut intraspecific populations was analyzed using morphological traits, the genetic diversity and population genetic structure for five geo-ecological groups using principles of molecular systematics and fluorescent-AFLP marker techniques, and the methods of constructing core collection were studied by morphology traits and molecular markers, respectively, in order to provide science evidence for conservation and utilization, to construct core collection of C. mollissima Bl. and breed the cultivated chestnut. The main results are as follows:1. The diversity of leaf, petiole and nut in 3 wild intraspecific populations (the Qinling Mountains ecotype, the Taiyi Mountains ecotype, and the Yanshan Mountains ecotype) of C. mollissima Bl. were investigated. The results indicated: There were significant differences among and within population. The morphological traits, such as leaf length, width, leaf shape index, length of petiole and nut shape, size, color, have great morphological diversity with variation coefficient (CV) of more than 10%. The range of nut weight varied from 1.69g to 3.89g in the Qinling Mountains population with CV 18.3%. The range and CV of leaf area and nut weight were the largest, and those of leaf shape index were the smallest; The content of main nutrition composition (water, total sugar, starch, protein, fat, ash and Vc) in ripe nuts determined in obtained 118 seedlings at the Qinling Mountains, the Taiyi Mountains and the Yanshan Mountains was analyzed and presented considerable genetic variations with CV of 6.2% - 28.3%, and the range and CV of the protein were the largest. There were the same trends in the 3 wild intraspecific populations;2. Compared with the diversity of the same trait in the different conditions, the result showed that, there was significant difference between site conditions with smallest CV in leaf area and nut weight and highest CV of Vitamin C contents in the Qinling Mountains; Correlation analysis revealed that mean weight of a single nut with annual rainfall and the longitude of each ecotype, in contrast, they were negatively correlated with the altitude. Vitamin C contents in the nuts from different ecotype were negatively regulated by annul rainfall. These relationships indicated that environmental conditions had impact on genetic diversity in Chinese wild chestnut.3. Population genetic structure was studied using fluorescent-AFLP markers on 120 Chinese Chesnut (Castanea mollisima Blume) accessions collected from the Yangtze River group, the Northern China group, the Northwest group, the Southeast group, and the Southwest group of fluorescent-AFLP markers. The purpose of this study was to determine the genetic structure and genotypic diversity amongst the different eco-geographical populations of Chinese chestnut. The results showed that the average number of polymorphic loci (A) was 180.88, the percentage of polymorphic loci (P) was 83.31% by 8 pairs of EcoR I /MseI (Mse I - a FAM fluorescent marked primer) primers in Chinese chestnut of five groups. Analysis for the average number of polymorphic loci (A) and the percentage of polymorphic loci (P) in five Chinese chesnut groups indicated that the Yangtze River group (A = 150.38; P = 73.80%)> the Northern China group (A = 147.75; P = 71.93%)> the Northwest group (A = 137.88; P = 68.00%)> the Southeast group (A = 90.50; P = 50.32%)> the Southwest China group (A = 86.00; P = 48.29%); Nei's gene diversity (H = 0.206) and Shannon information index (I = 0.326) at species level was significant or high significant higher than at group level. At group level, Nei's gene diversity and Shannon information index (H = 0.191; I = 0.302) in the Yangtze River group was higher than those in the Northern China group (H = 0.185; I = 0.295)and in the Northwest group(H = 0.182; I = 0.289), there were no significant differences; but they were significant higer than those in the Southeast group(H = 0.142; I = 0.229)and the Southwest group(H = 0.139; I = 0.218).The analysis of five population diversity and genetic structure from five geo-ecological groups showed that genetic diversity of wild chestnut population in the Yangtze Group was most abundant. This suggested that chestnut originated in the Yangtze geo-ecological group, then diffused to the northern China and the southern China by natural factors.4. The parameters--genetic differentiation coefficient and gene flow of population genetic structure in wild chestnut were analyzed in this study. Genetic differentiation coefficient (Gst = 0.0952) for five wild chestnut groups showed that wild chestnut genetic variation was mainly within the groups and accounted for 90.48% of total variations. The genetic variation between groups accounted for 9.52% of total variations. The gene flow Nm was 4.752 according to the genetic differentiation coefficient between groups (Gst = 0.0952). This indicated that there are partly gene exchanges among five wild chestnut groups. It is suggested that the main way of gene exchanges could be main factors of the long distance gene flow, natural climate, geographical barriers geography distance et al.5. Nei's genetic identities in five wild chestnut groups were between 0.8876 - 0.9665. Genetic distances were between 0.0341 - 0.1193. It was suggested that there were higher similarity between various geo-ecological groups in wild chestnut and lower genetic distance. The similarity between the Southwest group and the Southeast group was highest (99.06%), which showed that genetic differentiation was lowest between both groups in wild chestnut. The results from UPGMA cluster analysis for five groups showed that the Southeast and Southwest wild chestnut in the southern China was clustered together firstly and the Northern China and Northwest wild chestnut in northern China, then the Yangtze Group and the Northern China and Northwest group were clustered together. This indicated further that the similarity between the Southeast group and the Southwest group wild chestnut was highest and genetic relationship was closest.6. The diversity of 7 leaf traits and 12 nut traits from 297 accessions of C. mollissima Bl. was used to study method for constructing C. mollissima Bl. core collection using morphology. The results showed that Mahalanobis distance was the much better than Euclidean distance; UPGMA, Ward's method and Complete linkage was better than Single linkage and Median method, and deviation sampling was more suitable than random sampling and preferred sampling for constructing core collection. When 20% accessions were selected, Mahalanobis distance and Ward's method using stepwise clustering combining with Deviation sampling can construct a most reprehensive core collection and was the most suitable method for constructing C. mollissima Bl. core collection.7. The method for constructing core collection of C. mollissima Bl. based on molecular markers data was proposed, according to fluorescent AFLP marker, using 120 accessions of C. mollissima Bl. Compared with the random sampling strategy, allele preferred sampling could construct more representative core collections. When 25 accessions of C. mollissima Bl. was selected, allele preferred sampling strategy combined with SM, Jaccard or Nei & Li genetic distances using stepwise clustering was the suitable method for constructing C. mollissima Bl. core collection.
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