| Apricot (Armeniaca Mill.) is an ancient deciduous fruit tree crop in the temperate zones, which originates in central Asia and China. Cultivated apricots in the world almost belong to this common apricot (A. vulgaris Lam.) species. But because of diversity of ecological inhabits and differences and selections of adaptability between apricot cultivars for ecological environments, and a long term domestication cultivation and selection by human being, apricot trees evolutes and forms different geo-ecological groups and sub-groups under different geo-ecological conditions. The Central Asian group (including Liguang apricot and Xinjiang cultivated apricot in China), the Dzhungar-Zailij group, the European group, and the Northern China group are most important distribution areas. The Central Asian group occupies an important position in the origination and evolution of apricot. Kuche, Kashi and Hetian sub-groups located in oasis zones around the Tarim basin in Southern Xinjiang, China are three dominant sub-groups within the Central Asian group. Using principles of molecular systematics and fluorescent-AFLP marker techniques, the genetic diversity and population genetic structure for four geo-ecological groups and three sub-groups in central Asian geo-ecological group were analyzed in order to exploring its evolutional processes and origin of apricot cultivars, and to provide molecular basis for further cultivar selection and breeding of cultivated apricots. The main results are as follows:1. Using fluorescent-AFLP marker techniques, we have analyzed population genetic diversity by 7 pair of fluorescent-AFLP (MseI—a FAM fluorescent marked primer) primers on 45 apricot (Armeniaca Mill.) types in the Dzhungar-Zailij group, the European group, and the Northern China group, Xinjiang cultivated apricot sub-group and Liguang apricot sub-group in the Central Asian group. The average number of polymorphic loci (A) in common apricot of four groups was 130.86, the percentage of polymorphic loci (P) was 60.58%. These indicated that genetic diversity in common apricot populations was abundant. Analysis for the average number of polymorphic loci (A) and the percentage of polymorphic loci (P) in four apricot groups indicated that the genetic diversity in the Dzhungar-Zailij group was most abundant (A = 94.14;P = 43.59%), then Xinjiang cultivated apricot sub-group in the Central Asian group (A = 89.14;P = 41.27%),the Northern China group (A = 85.71;P = 39.68%), the European group(A = 85.14;P = 39.42%)in order, the genetic diversity in Liguang apricot sub-group in the Central Asian group was lowest (A = 81.14;P = 37.57%).2.Nei's gene diversity and Shannon information index of four common apricot groups indicated that Nei's gene diversity(H = 0.143) and Shannon information index (I = 0.226)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 = 0.131;I = 0.202) in the Dzhungar-Zailij group was higher than that in the Xinjiang cultivated apricot sub-group in the Central Asian group(H = 0.127;I = 0.195), in the European group(H = 0.124;I = 0.189), in the Northern China group (H = 0.116;I = 0.180),but there was no significant differences, was significant higher than that in the Liguang apricot sub-group in the Central Asian group (H = 0.113;I = 0.173). At the same time there were no significant differences of Nei's gene diversity and Shannon information index among Xinjiang cultivated apricot sub-group in the Central Asian group, the Northern China group, the European group and Liguang apricot sub-group in the Central Asian group3. The parameters--genetic differentiation coefficient and gene flow of population genetic structure in common apricot were analyzed in this study. Genetic differentiation coefficient (Gst = 0.147) for four apricot groups showed that apricot genetic variation was mainly within the groups and accounted for 85.3% of total variations. The genetic variation between groups accounted for 14.7% of total variations. The gene flow Nm was 2.901 according to the genetic differentiation coefficient between groups (Gst = 0.147). this indicated that there are partly gene exchanges among four apricot groups. It is suggested that the main way of gene exchanges could be human introduction of occasional seedling and geographical barriers could be main factor of hindering gene exchanges.4. Nei's genetic identities in four common apricot groups were between 0.9662-0.9906. Genetic distances were between 0.0095-0.0345. It was suggested that there were higher similarity between various geo-ecological groups in common apricot and lower genetic distance. The similarity between the Dzhungar-Zailij group and Xinjiang cultivated apricot sub-group in the Central Asian group was highest (99.06%). It indicated that Xinjiang cultivated apricot sub-group in the Central Asian group could be evoluted directly from the Dzhungar-Zailij group. Otherwise the similarity between the Dzhungar-Zailij group and the European group was lowest, which showed that genetic differentiation was highest between both groups in common apricot.5. The results from UPGMA cluster analysis for four groups showed that the Dzhungar-Zailij group and Xinjiang cultivated apricot sub-group in the Central Asian group was clustered together firstly and Liguang apricot sub-group in the Central Asian group, the Northern China group and the European group were clustered together. This indicated further that the similarity between the Dzhungar-Zailij group and Xinjiang cultivated apricot sub-group in the Central Asian group was highest and genetic relationship was closest.6. The analysis of four population diversity and genetic structure from four geo-ecological groups suggested that common apricot originated in the Dzhungar-Zailij geo-ecological group, then diffused to central Asia and formed cultivated apricot center in central Asia by domestication. It was further disseminated by human introduction to the East and formed the Northern China group, and to the West and formed the European group.7. UPGMA cluster analysis for 45 types of common apricot and 3 species in outgroup (A. mume, A. sibirica, A. mandshurica) combined with research results by other scientists were considered tentatively that evolution trend of apricot genus was: A. vulgaris→A. mandshurica→A. sibirica→A. mume.8. The genomic DNA of eighty-five cultivar samples from three sub-groups (Kuche sub-group, Kashi sub-group, and Hetian sub-group) in the central Asia group were tested for genetic diversity using AFLP analysis with 8 selected primer pairs. The results indicated that the genetic diversity in Kuche sub-group (A = 965;P = 60.01%;H = 0.1492;I = 0.2343)was most abundant, then Hetian sub-group (A = 879;P = 54.66%;H = 0.1465;I = 0.2273), the genetic diversity in Kashi sub-group(A = 867;P = 53.92%;H = 0.1283;I = 0.2030)was lowest. This indicated that Kuche sub-group has a more wide foreground in common apricot cultivar selection and breeding.9.The genetic differentiation coefficient Gst between three sub-groups in the central Asia group was 0.0882. The genetic variation was mainly within the sub-groups and accounted for 91.18% of total variations. The genetic variation between sub-groups accounted for 8.82% of total variations. According to the genetic differentiation coefficient, Gene flow Nm between the sub-groups was 5.1689. It could be main way of gene exchanges by human occasional seedling introduction.10. Population Nei's genetic identity IN and genetic distance D for three sub-groups in the central Asia group showed that the similarity between Kuche sub-group and Kashi sub-group was the highest (98.11%) and genetic distance was closest. The similarity between Kashi sub-group and Hetian sub-group was lowest (97.72%) and genetic distance was the largest, the genetic differentiation was larger.11. The results from UPGMA cluster analysis for 85 cultivars in three sub-groups showed that most cultivars in Kuche sub-group, Kashi sub-group and Hetian sub-group could be clustered together and only a few of cultivars were mixed together. It suggested that Kuche sub-group, Kashi sub-group and Hetian sub-group in the central Asia group were a relatively independent Mendelian populations. But at the same time, there were partly gene exchanges.12. Combined with the analysis of population genetic diversity and genetic structure in four geo-ecological groups and three sub-groups in the central Asia group, it was suggested that the apricot cultivars of Southside of Tianshan Mountain, Xinjiang were, geographically, evolved probably from the Ily wild apricots located in the North side of Tianshan Mountain. It was first introduced to Kuche from the primitive origin center, then, was further disseminated along the Silk Road to the East and the West.
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