Genetic Diversity Of Chinese Jujube Based On Nuclear SSR And Chloroplast SSR Markers

Chinese jujube belonged to genus Ziziphus in family Rhamnaceae and it is an important nonwood forest tree native to China. There are rich germplasm resources in cultivated jujube(Z. jujuba var. jujuba) and wild jujube(Ziziphus jujuba var spinosa). And abundant genetic diversity generated in the long-term process of artificial selection and natural selection. In this study, 298 representative accessions were selected(213 cultivated jujubes and 85 wild jujubes), with 10 pairs of nSSR and 7 pairs of cpSSR markers. We studied the genetic diversity, genetic structure, chlorotype median network, and the domestication relationship of Chinese jujube. Mainly got the following research conclusions:(1) According to the genetic diversity index(Na, Ne, Ho, He, h, F and I), the genetic diversity was more abundant in wild jujube population. In the nuclear genome level, He(wild jujube) was 0.750, greater than cultivated jujube’s(0.736), I(wild jujube) was 1.797, greater than cultivated jujube’s(1.604); In the chloroplast genome level, h(wild jujube) was 0.462, greater than cultivated jujube’s(0.418), I(wild jujube) was 0.809, greater than cultivated jujube’s(0.738). And it was certified by Nei’s genetic distance, the analysis of molecular variance(AMOVA) and the special allelic variations in populations, that cultivated jujube and wild jujube were closely related(Nei’s genetic distance was 0.191), and differentiated in a low degree(respectively 10% and 1% in cytoplasmic and nuclear level).(2) Through population structure analysis by nSSR, Chinese jujube were best divided into 2 groups(K=2). One was distributed in the middle and lower reaches of the Yellow River, presenting to be a wild jujube group(WJP). And the other was a cultivated jujube group(CJP), widely distributed in China. When K value increased to 7, WJP was classified into 2 subgroups, wild jujube and small-fruit cultivated jujube; CJP was classified into 5 subgroups with different phenotypic and geographic characteristics.(3) An primal wild jujube cluster(CH-2, 4 trees in it), 3 of which were old wild jujubes(Heshui old wild jujube in Gansu, Pingdingshan old wild jujube in Henan and Jimo old wild jujube in Shandong), was found through the chlorotype median network. Two independent clusters(CH-1 and CH-3), were evolved based on CH-2. And the evolution paths from wild jujube to cultivated jujube were revealed. Based on nSSR and cpSSR, the phylogenetic tree showed that gene exchange and introgression happened frequently, and further proved the low degree of genetic differentiation among cultivated jujube and wild jujube.In summary, abundant genetic diversity was detected in Chinese jujube, and genetic diversity of wild jujube was richer than that of cultivated jujube. They had close genetic relationship and low genetic differentiation. Gene exchange and introgression happened frequently in the process of evolution and domestication of cultivated jujube, which originated from wild jujube, and the evolutionary routes were multiple. Chinese jujube can be divided into two independent mixed groups based on nSSR and cpSSR, and they were evolved from a primitive wild jujube group. The study provides molecular evidence for the origin and domestication of Chinese jujube.