Abstract
Ziziphus is an important genus within the family Rhamnaceae. This genus includes several important fruit tree species that are widely planted in China and India, such as the Chinese jujube (Ziziphus jujuba Mill.), the wild jujube (Z. acidojujuba), and the Indian jujube (Z. mauritiana). However, information about their domestication based on the chlorotype diversity of Chinese jujube population is lacking. In this study, chloroplast microsatellite (cpSSR) markers were developed and used to investigate the genetic relationships between and domestication of jujube cultivars and wild jujube populations. Primer sets flanking each of the 46 cpSSR loci in non-coding regions of the chloroplast genome sequence of Z. jujuba Mill. cv. ‘Junzao’ were designed. In total, 10 markers showed polymorphisms from 15 samples (9 jujube cultivars and 6 wild jujube individuals), of which 8 loci were due to variations in the number of mononucleotide (A/T) repeats and 2 were due to indels. Six cpSSR markers were used in further analyses of 81 additional samples (63 jujube cultivars, 17 wild jujube samples, and 1 Indian jujube). Using these cpSSR markers, the number of alleles per locus ranged from two to four. In general, the Shannon Index (I) for each cpSSR ranged from 0.159 to 0.1747, and the diversity indices (h) and uh were 0.061 to 0.435 and 0.062 to 0.439, respectively. Seven chlorotypes were found; the Indian jujube showed distinct chlorotypes, and both the Chinese and wild jujube had four chlorotypes and shared two chlorotypes. A dominant chlorotype (G) accounted for 53 of 72 jujube cultivars and 13 of 23 wild jujube individuals. All chlorotypes were highly localized along the Yellow River, from the mid- to the lower reaches, suggesting a wide origin of jujube. These cpSSR markers can be applied to population and evolution studies of Chinese jujube and wild jujube.
Highlights
Ziziphus is an important genus in the family Rhamnaceae [1]
Six chloroplast SSRs (cpSSR) markers showed a total of 14 alleles in jujube and wild jujube, which suggested a high level of sequence conservation between closely related species; i.e., jujube and wild jujube
The polymorphic simple sequence repeats (SSR) markers could be amplified in Z. mauritiana, indicating that they could be used as cross-species markers within Ziziphus
Summary
Three economically important species in this genus are widely cultivated: the Chinese jujube (Z. jujuba), the wild (or sour) jujube (Z. acidojujuba), and the Indian jujube (Z. mauritiana). Chinese jujube (hereafter referred to as jujube) is believed to be native to China and is often considered as the generic species of the genus Ziziphus [2]. Jujubes are among the most popular native fruit trees in China and have been cultivated for dietary and medical uses for more than 3000 years; they are widely embedded in traditional Chinese culture [3]. Jujube plantations cover more than 1.53 million ha according to the China Forestry Yearbook 2013, and jujube is the fourth highest-ranking fruit produced in terms of economic importance after the apple, pear, and grape in the temperate regions of China. Jujube and wild jujube have been treated as two independent species [1]; the taxonomic delineation between them is still debated, and the history of the domestication of jujube remains unresolved
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