Munro's globemallow [Sphaeralcea munroana (Douglas) Spach] (Malvaceae), a herbaceous perennial endemic to the Great Basin of western North America, is an important candidate for use in horticulture and restoration. This species is able to tolerate drought, extreme temperatures, and establish on a variety of soil types. It serves as an important host for native pollinators, provides soil stabilization, and is a source of food for myriad mammals (Beale and Smith, 1970; Pendery and Rumbaugh, 1986; Rumbaugh et al., 1993). Currently, the lack of successful in and ex situ germination resulting from seed dormancy limits its use in restoration. Few sources explore the dormancy mechanisms and methods that induce germination in Sphaeralcea spp. (Page et al., 1966; Roth et al., 1987).
Vleeshouwers et al. (1995) describe seed dormancy as a state “the degree of which defines what conditions should be met to make the seed germinate.” These conditions are characterized based on the mechanisms that prevent germination. Physically dormant seeds have a palisade layer of lignified cells that prevents water imbibition (Corner, 1951; Vazquez-Yanes and Perez-Garcia, 1976). Although a number of species in the Sphaeralcea genus have been observed to benefit from scarification, the cause of dormancy has not been examined directly (Page et al., 1966; Roth et al., 1987; Sabo et al., 1979; Smith and Kratsch, 2009). In these species, imbibition (critical for germination) is regulated by a water gap structure located within the seedcoat. The water gap can become permeable after exposure to temperature flux, drying, or scarification, thus allowing imbibition into an otherwise impermeable seed (Baskin, 2003; Baskin and Baskin, 1998; Baskin et al., 2000).
Ex situ, chemical and mechanical scarification has been used to improve germination of physically dormant seeds (Baskin and Baskin, 1998; Hoffman et al., 1989; Page et al., 1966; Roth et al., 1987). For example, Page et al. (1966) reported an up to 40% increase in germination of S. grossulariifolia after submergence in sulfuric acid, a substantial improvement compared with the control (0%). Similarly, submergence of Sphaeralcea seeds in 18 M sulfuric acid for 10 min improved germination of S. coccinea and two accessions of S. grossulariifolia (77%, 69%, and 62%) relative to the controls (5%, 14%, and 32%), but failed to do so for S. munroana (8%) compared with the control (2%) (Roth et al., 1987). Organic solvents have also been used to promote germination of physically dormant seeds. Page et al. (1966) reported 67% germination of treated S. grossulariifolia seeds after a 4-h submergence in diethyl dioxide vs. 0% germination of untreated seeds. Roth et al. (1987) found a 3-h submergence of S. coccinea, S. munroana, and two accessions of S. grossulariifolia in diethyl dioxide to significantly enhance germination (36%, 53%, 89%, and 68%) compared with the control (5%, 2%, 14%, and 32%). Despite the effectiveness of chemical scarification, chemicals can be hazardous, difficult to obtain, and present serious health risks (Mallinckrodt Baker, 2008a, 2008b).
Mechanical scarification has also been reported to boost germination rates of physically dormant seeds of Malvaceae species. The International Seed Testing Association recommends scarification (pierce, chip, or file off seedcoat) for Althaea hybrids (Malvaceae) (ISTA, 2011). In addition, Baskin and Baskin (1997) observed 100% germination after abrasion of Iliamna corei (Malvaceae) seeds.
Despite evidence for the presence of physical dormancy, reported germination of S. munroana has failed to exceed 53%, even when dormancy was presumably broken (Roth et al., 1987; Smith and Kratsch, 2009). Thus, it is unclear whether these seeds possess additional dormancy types. Physiological dormancy, characterized by the presence of chemical inhibitors that prevent embryonic growth, is commonly found in cold desert herbaceous perennials and can be relieved by stratification (Baskin and Baskin, 1998). In addition, gibberellic acid (GA3) has been successful in alleviating the chemical constraints that prevent radical emergence and increasing embryonic growth in a number of physically dormant species (Bewley, 1997; Hilhorst, 1995; Koornneef et al., 2002; Leubner-Metzger, 2003).
Although less common, the coupling of physical and physiological dormancy (i.e., combined dormancy) requires both types to be broken before germination can occur (Baskin and Baskin, 1998; Emery, 1987). Dunn (2011) reports increased germination of Sphaeralcea ambigua and S. coccinea (45% and 85%) compared with the control (18% and 5%) after a 30-d stratification of scarified seeds. Similarly, Smith and Kratsch (2009) report that pairing mechanical scarification (nicking of the seedcoat) with a 6-week stratification at 4 °C resulted in higher germination of the bulked seeds of S. grossulariifolia, S. parvifolia, and S. munroana than either treatment alone, suggesting that seeds of S. munroana may exhibit combined dormancy.
The process of seed imbibition and the site of water entry are critical to our comprehension of the germination dynamics and treatment effects. To address these questions, three experiments were initiated. The first experiment 1) compared water uptake of non-treated, mechanically scarified, and boiling water scarified seeds; and 2) identified the primary site of water uptake. The second experiment investigated the germination response of fresh S. munroana seeds to mechanical scarification with a sharp blade, 6-week stratification, and their combination. The third experiment evaluated the germination behavior of stored seeds after mechanical scarification, submergence duration in gibberellic acid solution or deionized (DI) water, and several combinations of these treatments.
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