Genetic Diversity Of 10 Walnut Populations In China

Genetic resource is the foundamental substance for plant breeding and geneticimprovement. China is one of the original places of walnut with abundant genetic resources.However, as the development of walnut industry and the extension of new varieties or lines,walnut genetic resource disappears gradually. So, it is necessary to investigate the geneticdiversity and genetic structure of walnut resource in existence by genetic marker and providesome theoretical information for further conservation and utilization.In this study, the genetic diversity and genetic structure of 10 walnut populations (4 for J.sigillata and 6 for J. regia) distributed in Yunnan, Sichuan, Henan, Shanxi, Xinjiang provinceswere investigated with SSR and morphological markers. Eight pair of SSR primers selectedfrom 32 pairs primers which were designed for J. nigra were employed in our research, and anoptimized PCR reaction system was adopted.The main results are the below:A moderate level of genetic diversity was observed at population levels with the totalnumber of alleles 73 and average 9.25 for per locus. The expected heterozygosity (H_e) withinpopulation changed from 0.271 to 0.687 and the total value was 0.663. The percentage ofpolymorphic loci(P) was 100%. Among the detected alleles, 58 alleles were shared by J. regiaand J. sigillata, while 7 and 8 alleles were private for J. regia and J. sigillata respectively. Thesequence of genetic diversity of the 10 populations was QZ＞LJ＞SJC＞YB＞MN＞ML＞LC＞FY＞HS＞GL.The population distributed in the southwest of China had a higher genetic diversity than thepopulations in other places.The proportion of genetic differentiation presented among populations accounted for26.1% of the whole diversity, and the F_ST value in J. regia populations(0.273) was apparentlyhigher than that in J. sigillata populations(0.073). Such extensive inter-populationdifferentiation detected in Juglans could be resulted from two main factors, restricted geneflow (N_m=0.708) between populations caused by habitat fragmentation and habitat diversity.The result of UPGMA clustering indicated that the 10 populations congregated according totheir geographic distribution rather than the definition of traditional taxonomy, supporting theviewpoint that the two species probably are different ecological types of the same species. In addition, the result of genetic diversity revealed by morphological marker in populationMN and HS suggested that the index of top leaf, thickness of hull and weight of fruit had alarger range of variation and the index of fruit shape was the smallest. All variation indexes of8 quantitive characters in population MN were higher than that of population HS. It suggestedthat the genetic diversity in population MN is higher than population HS, white was consistentwith the result revealed by SSR marker.