Study Of Population Structure And Diversity In Carya Cathayensis Sarg

With AFLP and SSR markers, the population structure and genetic diversity of hickory (Carya cathayensis), an important non-timber species in Zhejiang Province, have been studied. The main achievements are as follows:An AFLP analysis system suitable for hickory has been established, the key points of which are: (1) the improved CTAB method was suited to DNA extraction from hickory leaves and extracted DNA was qualified for AFLP analysis; (2) an enzyme-cut combination of EcoR I/Mse I and a one-step method for enzyme cutting and adaptor ligation were adopted; and (3) the primer pairs screened from 256 pairs of primers for AFLP analysis in hickory were E-ACG+M-CTG, E-AAT+M-CCC, E-AGT+M-CCC, E-AGT+M-CGT, E-AAT+M-CGA, E-AGA+M-CCA, E-AGT+M8CCA and E-AGA+M-CGC. The amplified products were electrophoresized in 6% denatured PAGE gel and silver stained then, with clearly identified bands obtained.With 8 pairs of primers, 32 polymorphic markers were generated in 100 samples collected from the natural hickory polulation, which indicated a low polymorphic level. There were 499 marker combinations for two-point analysis, 60 of which showed significant in LD and accounted for 12.10% of the total combinations and there were 4952 marker combinations for three-point analysis, 779 of which showed significant in LD and accounted for 15.70% of the total.The study has shown that there exists significant LD in natural population of hickory and there are close linkage among alleles, a low recombination rate, a low heterozygosity and a low genetic diversity. The regional distribution of hickory is limited and separated from other species of the same genus with no gene flow, from which it can be inferred that hickory population has experienced bottleneck during development and evolution, accompanied by significant genetic drift. This evolutionary process can create a significant LD. Semi-sib offspring similar to their maternal parent at the molecular level indicates that most of the pairs of loci in LD are derived from maternal parent reflecting the phenomenon of homeologus pairing and there might exist the phenomenon of apomixes.LD analysis based on AFLP analysis of natural population in hickory, a woody non-timber species, has supported the model developed by Wu's group for LD estimation and testing with dominant markers used in underrepresented tree species and is the application of this model to tree species. Meanwhile, the result also confirms the idea that three-locus analysis has more chances to detect the significance of linkage disequilibria for the same marker pair than two-locus analysis.AFLP analysis of both maternal parents and their semi-sib offspring has also shown a low lever of DNA polymorphism and there is little difference between maternal parent and its semi-sib offspring.19 pairs of SSR primers developed by Americans from pecan are not suitable for hickory although both pecan and hickory are two species of one genus.