Influences of environmental factors on leaf morphology of Chinese jujubes.

Rainfall and temperature are the primary limiting factors for optimum quality and yield of cultivated jujube (Ziziphus jujuba Mill.). Adaptation to arid and cool environments has been and remains an important goal of many jujube improvement programs. This study summarized the survey results of 116 Chinese jujube varieties grown at 33 sites in China. The objective was to identify the environmental factors that influence leaf morphology, and the implications for breeding and introduction of new jujube varieties. Jujube leaf morphological traits were evaluated for their potential relationships with mean annual temperature (MAT) and mean annual precipitation (MAP). The results showed that many leaf morphological traits had a strong linear relationship with local precipitation and temperature. Longer veins per unit area (VLA) and reduced leaf area and leaf perimeter were typical of arid areas. VLA was inversely related to MAT and MAP at the centers of origin of jujube. There was a positive relationship between leaf shape (perimeter2/area) and both MAT and MAP. These results indicated that leaf vein traits of Chinese jujubes might have resulted from their adaptation to environmental factors in the course of long-term evolution. Principal component analysis allocated the 116 jujube varieties to three different groups, differentiated on the basis of morphological and physiological leaf characteristics. Jujube varieties from the Hebei, Shandong, Henan, southern Shanxi and central Shaanxi provinces were closely related, as were varieties from northwest Shanxi and northeast Shaanxi provinces, and varieties from the Gansu and Ningxia provinces. These close relationships were partially attributed to the frequent exchanges of varieties within each group. Leaf venation characteristics might be used as reference indices for jujube variety introduction between different locations.

In vitro induction of tetraploid plants from diploid Zizyphus jujuba Mill. cv. Zhanhua.

Tetraploid plants of Zizyphus jujuba Mill. cv. Zhanhua were obtained with in vitro colchicine treatment. Shoot tips from in vitro-grown plants were treated with five different concentrations of colchicine (0.01, 0.03, 0.05, 0.1, 0.3%) in liquid MS medium (Murashige and Skoog 1962), and shaken (100 rpm) at 25 degrees C in darkness for 24, 48, 72 or 96 h, respectively. Tetraploids were obtained at a frequency of over 3% by using 0.05% colchicine (48 h, 72 h) and 0.1% colchicine (24 h, 48 h) treatment as determined by flow cytometry. Cytological and morphological evidence confirmed the results of flow cytometric analysis. The chromosome number of diploid plants was 24 and that of tetraploid plants was 48. The stomata sizes of tetraploid plants were significantly larger than those of diploid plants, while the frequency of stomata were reduced significantly. Similarly, the chloroplast number of guard cells of tetraploid plants increased significantly. The selected tetraploid plants were grafted onto mature trees of Z. jujuba Mill. cv. Zhanhua in the field, resulted in thicker stems, rounder and succulent leaves, larger flowers and a delay in florescence time (3-4 days later) than diploid plants.