Chemical Scarification, Moist Prechilling, and Thiourea Effects on Germination of 18 Shrub Species

Abstract

Establishment is a major problem of increasing palatable shrubs on rangeland; therefore the objective of this study was to determine the effects of chemical scarification, moist prechilling, and thiourea on seed germination in 18 different shrub species. Scarification for various periods in concentrated sulfuric acid, 10%S hydrogen peroxide, and 5.25% sodium hypochlorite (clorox) produced unchanged or reduced germination, except for one hydrogen peroxide treatment of bitterbrush. Moist prechilling prior to germination was conducted on vermiculite moistened with distilled water or 0.2% potassium nitrate for periods up to 16 weeks. In general, prechilling yielded maximum germination, without respect to moistening agent. Seeds treated with thiourea were soaked for periods up to 1 hr in a 0.3% solution. Thiourea treatments were ineffective in increasing germination. On the basis of their germination response to prechilling treatments, bitterbrush, shadscale, big sagebrush, cliffrose, curileaf mountain mahogany, and golden currant are recommended for fall planting. Apache plume, shrubby cinquefoil and Morman tea could be planted in spring or fall, and winterfat, fourwing saitbush, and Jersey tea should be planted in spring. Constraints other than seed germination, not studied here, must also be considered in planting shrubs for range improvement. The importance of seasonal availability of palatable range shrubs and their adaptation and establishment on selected range sites has received little attention in other than the western range states. This area of range improvement is recognized in the western states (Cable 1972; Stevens et al. 1977) but direct seeding of desirable native shrubs has met with limited success. Poor stands are often attributed to poor seed germination. Seeds which do not germinate under favorable conditions, but may be induced to germinate, are considered dormant (Mayer and Poljakoff-Mayber 1975). Immature embryos, impermeability of seed coat to water or gases, mechanical causes, light and temperature requirements, or the presence of germination inhibitors are factors which may cause seed dormancy. Chemical and mechanical scarification, stratification, subjecting seeds to temperature extremes, soaking seeds in various concentrations of thiourea solutions, gibberellic acid, and combinations of one or more treatments have been used to break seed dormancy (Carlson 1974; Everett and Meeuwing 1975; Liacos and Nord 1961; McConnell 1960; McHemy and Authors are graduate research assistant; research agronomist, SEA-USDA: associate professor of range science; and associate professor of statistics, Oklahoma State Univ., Stillwater 74074. This research is a contribution of the Oklahoma Agricultural Experiment Station as Journal Article No. 3587. At present Stidham is environmental specialist, Shell Oil Company, Houston, Texas. Manuscript received January 5, 1979. Jensen 1967; Pearson 1957; Walters 1970). A hard seed-coat may be imperneable to water, gases, or may constrain the embryo. Scarification (seed coat abrasion/ erosion) treatments are used to erode the seed-coat to improve permeability (Amen 1963). Stratification (moist chilling) is believed to limit the effects of inhibitors while promoting growth stimulators such as gibberellic acid. Dilute solutions of potassium nitrate and gibberellic acid are growth stimulators and different concentrations have been used to promote gennination of certain species (Mayer and Paljakoff-Mayber 1975; Young et al. 1978). Mirov (1936) observed that stratification treatments increased germination of seeds from plants growing at elevations greater than 1,200 m, while scarification treatments, in some instances, increased germination for species growing at elevations less than 300 m. Considerable difficulty has been encountered by others in establishing palatable shrub species by direct seeding. With this in mind, the objective of our study was to deternine the effects of different pre-gennination treatments on germination of 18 shrub species, from diverse origins.