One of the most important attributes of a genome is genome size, which can to a large extent reflect the evolutionary history and diversity of a plant species. However, studies on genome size diversity within a species are still very limited. This study aims to clarify the variation in genome sizes of Chinese jujube and sour jujube, and to characterize if there exists an association between genome sizes and geographical variation. We measured the genome sizes of 301 cultivars of Chinese jujube and 81 genotypes of sour jujube by flow cytometry. Ten fruit traits, including weight, vertical diameter, horizontal diameter, size, total acids, total sugar, monosaccharide, disaccharide, soluble solids, and ascorbic acid were measured in 243 cultivars of Chinese jujube. The estimated genome sizes of Chinese jujube cultivars ranged from 300.77 Mb to 640.94 Mb, with an average of 408.54 Mb, with the highest number of cultivars (20.93%) falling in the range of 334.787 to 368.804 Mb. The genome size is somewhat different with geographical distribution. The results showed weakly significant positive correlation (p
< 0.05) between genome size and fruit size, vertical diameter, horizontal diameter, and weight in the Chinese jujube. The estimated sour jujube genome sizes ranged from 346.93 Mb to 489.44 Mb, with the highest number of genotypes (24.69%) falling in the range of 418.185 to 432.436 Mb. The average genome size of sour jujube genotypes is 423.55 Mb, 15 Mb larger than that of Chinese jujube. There exists a high level of variation in genome sizes within both Chinese jujube cultivars and sour jujube genotypes. Genome contraction may have been occurred during the domestication of Chinese jujube. This study is the first large-scale investigation of genome size variation in both Chinese jujube and sour jujube, which has provided useful resources and data for the characterization of genome evolution within a species and during domestication in plants.
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