Autotetraploidization Alters Morphology, Photosynthesis, Cytological Characteristics and Fruit Quality in Sour Jujube (Ziziphus acidojujuba Cheng et Liu)

Artificially induced polyploidization is one of the most effective techniques for improving the biological properties and creating new cultivars of fruit trees. Up to now, systematic research on the autotetraploid of sour jujube (Ziziphus acidojujuba Cheng et Liu) has not been reported. 'Zhuguang' is the first released autotetraploid sour jujube induced with colchicine. The objective of this study was to compare the differences in the morphological, cytological characteristics, and fruit quality between diploid and autotetraploid. Compared with the original diploid, 'Zhuguang' showed dwarf phenotypes and decreased tree vigor. The sizes of the flowers, pollen, stomata, and leaves of 'Zhuguang' were larger. Perceptible darker green leaves were observed in 'Zhuguang' trees owing to increased chlorophyll contents, which led to higher photosynthesis efficiency and bigger fruit. The pollen activities and the contents of ascorbic acid, titratable acid, and soluble sugar in the autotetraploid were lower than those in diploids. However, the cyclic adenosine monophosphate content in autotetraploid fruit was significantly higher. The sugar/acid ratio of autotetraploid fruit was higher than that of diploid fruit, which made the autotetraploid fruit taste different and better. The results indicated that the autotetraploid we generated in sour jujube could greatly meet the goals of our multi-objective optimized breeding strategies for improving sour jujube, which includes tree dwarfing, increased photosynthesis efficiency, and better nutrient values and flavors as well as more bioactive compounds. Needless to say, the autotetraploid can also serve as material for generating valuable triploids or other types of polyploids and are also instrumental in studying the evolution of both sour jujube and Chinese jujube (Ziziphus jujuba Mill.).