Relationship of black-tip disorder in jujube fruits to sugar transportation and accumulation

Abstract

Black-tip disorder, an ailment in the fruits of the Hupingzao cultivar of jujube trees (Ziziphus jujuba Mill. ‘Hupingzao’), seriously affects the edible quality of the fruits. To characterize the relationship between the disorder and sugar transport capacity, transportation of soluble sugar in the vascular bundles of Hupingzao fruits was analyzed using UPLC and the fluorescence tracing method. Phloem cell viability of the vascular bundles was also analyzed by staining. Results showed that black-tip disorder mainly occurred from the white-ripe period onwards during the development of Hupingzao fruits, and disease spots only appeared in the blossom end of the fruits. There was a significantly higher rate of large disorder fruits than small disorder fruits. The accumulation and transportation rate of soluble sugar in the blossom end of the fruits was significantly lower than that in the shoulder regions from the white-ripe period onwards. At the same developmental stage, the soluble sugar content in the blossom end of disorder fruits was significantly lower than that in the blossom end of healthy fruits. In disorder fruits, the soluble sugar content of large fruits was lower than that of small fruits. In disorder fruits, phloem activity was weaker in large fruits than small fruits. In summary, the ability of the vascular bundles to transport soluble sugar weakened and sugar supply in the blossom end of the fruits was insufficient to sustain health, and this was likely to cause black-tip disorder from the white-ripe period onwards during the development of Hupingzao fruits.