HORTSCIENCE 46(12):1672–1676. 2011. after submergence in sulfuric acid, a substan- tial improvement compared with the control (0%). Similarly, submergence of Sphaeralcea Overcoming Dormancy and seedsin18Msulfuricacidfor10minim- proved germination of S. coccinea and two Enhancing Germination of accessions of S. grossulariifolia (77%, 69%, and 62%) relative to the controls (5%, 14%, Sphaeralcea munroana Seeds and 32%), but failed to do so for S. munroana (8%) compared with the control (2%) (Roth Olga A. Kildisheva et al., 1987). Organic solvents have also been Center for Forest Nursery and Seedling Research, College of Natural used to promote germination of physically Resources, University of Idaho, P.O. Box 441133, Moscow, ID 83843 dormant seeds. Page et al. (1966) reported 67% germination of treated S. grossulariifolia R. Kasten Dumroese seeds after a 4-h submergence in diethyl USDA Forest Service Rocky Mountain Research Station, 1221 South Main dioxide vs. 0% germination of untreated seeds. Roth et al. (1987) found a 3-h sub- Street, Moscow, ID 83843 mergence of S. coccinea, S. munroana,and Anthony S. Davis1 two accessions of S. grossulariifolia in diethyl dioxide to significantly enhance ger- Center for Forest Nursery and Seedling Research, College of Natural mination (36%, 53%, 89%, and 68%) com- Resources, University of Idaho, P.O. Box 441133, Moscow, ID 83843 pared with the control (5%, 2%, 14%, and Additional index words. Munro’s globemallow, Malvaceae, germination, imbibition, water 32%). Despite the effectiveness of chemical scarification, chemicals can be hazardous, gap, gibberellic acid difficult to obtain, and present serious health Abstract. The results of a series of experiments involving a variety of dormancy-breaking risks (Mallinckrodt Baker, 2008a, 2008b). treatments indicate that Munro’s globemallow [Sphaeralcea munroana (Douglas) Spach] Mechanical scarification has also been seeds are physically dormant, possess a cap-like structure in the occlusion of the water reported to boost germination rates of phys- gap, which inhibits imbibition, and can be artificially dislodged through boiling water ically dormant seeds of Malvaceae species. scarification. The highest germination capacity (93%) was achieved by mechanical The International Seed Testing Association scarification of previously stored seeds. Exogenous application of a gibberellin solution recommends scarification (pierce, chip, or file and cold stratification failed to enhance germination compared with scarification alone, off seedcoat) for Althaea hybrids (Malvaceae) indicating an absence of additional dormancy types. These results should improve the (ISTA, 2011). In addition, Baskin and Baskin usefulness of this drought-tolerant perennial for landscaping and restoration given its (1997) observed 100% germination after abra- effectiveness in soil stabilization, tolerance to a variety of soil types, extreme tempera- sion of Iliamna corei (Malvaceae) seeds. tures, and ecological importance. Despite evidence for the presence of physical dormancy, reported germination of S. munroana has failed to exceed 53%, even Munro’s globemallow [Sphaeralcea dormancy limits its use in restoration. Few when dormancy was presumably broken munroana (Douglas) Spach] (Malvaceae), a sources explore the dormancy mechanisms (Roth et al., 1987; Smith and Kratsch, herbaceous perennial endemic to the Great and methods that induce germination in 2009). Thus, it is unclear whether these seeds Basin of western North America, is an im- Sphaeralcea spp. (Page et al., 1966; Roth possess additional dormancy types. Phys- portant candidate for use in horticulture and et al., 1987). iological dormancy, characterized by the restoration. This species is able to tolerate Vleeshouwers et al. (1995) describe seed presence of chemical inhibitors that prevent drought, extreme temperatures, and establish dormancy as a state ‘‘the degree of which embryonic growth, is commonly found in on a variety of soil types. It serves as an defines what conditions should be met to make cold desert herbaceous perennials and can be important host for native pollinators, provides the seed germinate.’’These conditions are char- relieved by stratification (Baskin and Baskin, soil stabilization, and is a source of food for acterized based on the mechanisms that pre- 1998). In addition, gibberellic acid (GA3) has myriad mammals (Beale and Smith, 1970; vent germination. Physically dormant seeds been successful in alleviating the chemical Pendery and Rumbaugh, 1986; Rumbaugh have a palisade layer of lignified cells that constraints that prevent radical emergence et al., 1993). Currently, the lack of successful prevents water imbibition (Corner, 1951; and increasing embryonic growth in a number in and ex situ germination resulting from seed Vazquez-Yanes and Perez-Garcia, 1976). Al- of physically dormant species (Bewley, 1997; though a number of species in the Sphaeralcea Hilhorst, 1995; Koornneef et al., 2002; genus have been observed to benefit from Leubner-Metzger, 2003). scarification, the cause of dormancy has not Although less common, the coupling of Received for publication 5 June 2011. Accepted for been examined directly (Page et al., 1966; physical and physiological dormancy (i.e., publication 24 Oct. 2011. Roth et al., 1987; Sabo et al., 1979; Smith and combined dormancy) requires both types Funding for this research was provided by the Kratsch, 2009). In these species, imbibition to be broken before germination can occur Idaho Transportation Department, the Great Basin Native Plant Selection and Increase Project, the (critical for germination) is regulated by a (Baskin and Baskin, 1998; Emery, 1987). University of Idaho Seed Grant Program, and the water gap structure located within the seed- Dunn (2011) reports increased germination University of Idaho Center for Nursery and Seedling coat. The water gap can become permeable of Sphaeralcea ambigua and S. coccinea Research. after exposure to temperature flux, drying, or (45% and 85%) compared with the control We thank Timothy R. Johnson for statistical support scarification, thus allowing imbibition into an (18% and 5%) after a 30-d stratification of and Nalin Suranjith Gama-Arachchige for assis- otherwise impermeable seed (Baskin, 2003; scarified seeds. Similarly, Smith and Kratsch tance in electron microscopy. We extend our Baskin and Baskin, 1998; Baskin et al., 2000). (2009) report that pairing mechanical scar- thanks to Sabry Elias, Nancy Shaw, Matthew M. Ex situ, chemical and mechanical scarifi- ification (nicking of the seedcoat) with a Aghai, Robert F. Keefe, Emily C. Overton, Matt cation has been used to improve germination 6-week stratification at 4 °C resulted in Fisk, and Erin Denney who provided technical support. of physically dormant seeds (Baskin and higher germination of the bulked seeds This article is a portion of a thesis submitted by Olga Baskin, 1998; Hoffman et al., 1989; Page of S. grossulariifolia, S. parvifolia,andS. A. Kildisheva in fulfilling a degree requirement. et al., 1966; Roth et al., 1987). For example, munroana than either treatment alone, sug- 1To whom reprint requests should be addressed; Page et al. (1966) reported an up to 40% gesting that seeds of S. munroana may exhibit e-mail [email protected]. increase in germination of S. grossulariifolia combined dormancy. 1672 HORTSCIENCE VOL. 46(12) DECEMBER 2011 The process of seed imbibition and the Expt. 2: scarification and stratification. to one of two mathematical models, the site of water entry are critical to our compre- This experiment assessed the presence of parameters of which give a detailed descrip- hension of the germination dynamics and physical, physiological, and combined dor- tion of seed behavior. This approach also treatment effects. To address these questions, mancy by comparing germination behavior alleviated the need for data transformation. three experiments were initiated. The first after exposure to a 1) control (dry, unaltered In Expt. 2, a three-parameter model was experiment 1) compared water uptake of non- seeds); 2) mechanical scarification (previ- used [Eq. (1)] in which G (t) is the cumulative treated, mechanically scarified, and boiling ously described); 3) 6-week stratification at germination percentage at time (t) expressed water scarified seeds; and 2) identified the 4.6 ± 0.02 °C on moistened blotter inside in days (d), Gc is germination capacity or the primary site of water uptake. The second sealed petri dishes; and 4) combined scarifi- germination asymptote at the end of the experiment investigated the germination cation + stratification treatment. The blotters testing period (%), GC50 is the time in days response of fresh S. munroana seeds to were remoistened with 5 mL of DI water required to reach 50% germination, and Gd is mechanical scarification with a sharp blade, every 3 d to avoid a potential reduction in the germination rate (% /day). As a result of 6-week stratification, and their combination. dormancy break resulting from substrate differences in germination behavior in Expt. The third experiment evaluated the germi- desiccation, which can result in lower oxygen 3, an alternative model that better fit this set nation behavior of stored seeds after mechan- availability (Flemion, 1931; Stokes, 1965). of data was used [Eq. (2)] in which Gd was ical scarification, submergence duration in Seeds in the combination treatment were replaced with Gl, defined as the time in days gibberellic acid solution or deionized (DI) scarified first (Smith and Kratsch, 2009). All to