Germination Requirements of Lotebush (Ziziphus obtusifolia var. obtusifolia)

Abstract

Optimum average temperatures for germination of lotebush (Ziziphus obtusifolia var. obtusifolia) seeds in the laboratory were 20? to 30?C. Although some germination occurred without light and without a cold treatment, both of these factors tripled germination when they were present. Aging was unnecessary to obtain optimum germination. Best emergence in the field occurred when average soil temperatures ranged from 22.4? to 27.1? C. These field temperatures are most common in early spring and early fall. Litter enhanced germination in late spring and summer. Timing of precipitation is a limiting factor during the warmest months. Lotebush (Ziziphus obtusifolia var. obtusifolia), a spiny shrub in the Rhamnaceae family, occurs in Texas, Arizona, New Mexico, and northern Mexico. Because of its ability to resprout from both crown and roots, along with its resistance to herbicides (Scifres and Kothmann 1976), lotebush has the potential to increase its cover on Texas rangeland after the release of competition from other woody vegetation by brush control treatments (Carter 1958, Box and White 1969). Moreover, since lotebush spreads by movement of seeds and requirements for germination are unknown, its ecological potential may be seriously underestimated. Temperature is not only a general environmental factor which affects the germination process, but may be a method for breaking the dormancy of some seeds. Seeds of many plants are shed in autumn and are exposed to cold temperatures during the winter while they may also be exposed to moist conditions in the soil or under leaf litter. Schopmeyer (1974) reported that Ziziphusjujuba seeds needed to be stratified for 60 to 90 days at 50 C in moist sand for maximum germination to occur. Light, important for breaking the dormancy of some seeds, is usually most abundant only on the soil surface. Seeds can be characterized by their light requirements as those which: (1) germinate after a brief illumination; (2) germinate only in continuous light; (3) germinate only in darkness; or (4) are indifferent to light during germination (Crocker 1948, Schopmeyer 1974, Mayer and Poljakoff-Mayber 1975). Percentage of creosotebush (Larrea tridentata) seeds which germinate is greater in darkness than in light (Barbour 1968), whereas, germination of big sagebrush (Artemisia tridentata) seeds exposed to full light was greater than when seeds were in the dark (Weldon et al. 1959). The indurante stone in each lotebush fruit has two cells, and each contains a seed resembling an apple (Malus pumila) seed (Lundell 1969). Common methods used to scarify seeds are mechanical abrasion (Schopmeyer 1974, Mayer and Poljakoff-Mayber 1975), passage through the digestive tracts of birds and herbivores (Mayer and Poljakoff-Mayber 1975), and fire (Cushwa et al. 1968). Other methods include acid, boiling water (Quick and Quick 1961, The authors are research assistant and chairman Horn professor, Department of Range and Wildlife Management, Texas Tech University, Lubbock 79409. This research is published as Texas Tech University, College of Agricultural Sciences Publication No. T-9-228. We thank J. W. Chapman and Sons Realtors for allowing us to conduct this study on their property. Manuscript received December 14, 1980. Schopmeyer 1974, Mayer and Poljakoff-Mayber 1975), and exposure to alternating low and high temperatures which cause the seedcoat to contract and expand (Mayer and Poljakoff-Mayber