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Tanglehead (Heteropogon contortus) is a native Hawaiian grass that has been used in restoration and has potential for expanded re-vegetation use. Although interest and demand for tanglehead re-vegetation has increased, the supply of tanglehead seeds has remained limited as a result of a lack of seed production protocols addressing seed dormancy. Smoke water from burning vegetation may provide an economical and practical seed treatment because aerosol smoke has been reported to stimulate tanglehead seed germination. Dose rate and side-by-side comparison studies were conducted to evaluate the germination stimulation efficacy of food-grade liquid smoke, xylose smokeinfused water, tanglehead smoke-infused water, karrikinolide (KAR1), and cyanide (i.e., mandelonitrile and potassium cyanide). Optimum smoke water dilutions were 1% v/v for food-grade liquid smoke and undiluted for xylose smoke-infused water and tanglehead smoke-infused water. KAR1 was not stimulatory at concentrations between 0.0067 and 66.7 mM. Potassium cyanide stimulated tanglehead seed germination at concentrations between 50 to 500 mM. Germination was promoted to even greater levels with the cyanohydrin, mandelonitrile, indicating a role for benzaldehyde (a byproduct of mandelonitrile decomposition) in stimulating tanglehead seed germination. Benzaldehyde was confirmed to be stimulatory at concentrations between 50 to 100 mM. The presence of cyanide at stimulatory levels was confirmed in tanglehead smoke-infused water (i.e., ’100 mM), but not in food-grade liquid smoke or xylose smoke-infused water. Germination with non-cyanide-containing smoke waters indicates the presence of other compounds in smoke that can stimulate tanglehead germination. In the side-by-side comparison study, food-grade liquid smoke (1% v/v) and undiluted tanglehead smokeinfused water provided consistent germination stimulation comparable to 500 mM potassium cyanide. Undiluted xylose smoke-infused water did not provide significant germination stimulation in the comparison studies. This may be the result of differences in seed batch sensitivity to the germination stimulant, seed storage duration as well as subtle differences in the preparation of xylose smoke-infused water. Tanglehead (Heteropogon contortus, Poaceae) or Pili grass (in Hawaiian) is a perennial C4 bunchgrass found on all main islands of the Hawaiian Archipelago and throughout the tropics (Wagner et al., 1999). In Hawaii, it is an important re-vegetation and restoration species as a result of its cultural and ecological significance (Daehler and Goergen, 2005) and ability to grow in low-resource conditions (i.e., low rainfall and low fertility soils) (USDA-NRCS, 2007). Over the past decade, tanglehead has been extensively used in restoration and re-vegetation of the uninhabited island of Kahoolawe (USDA-NRCS, 2007) as well as some offshore islands around Oahu (Smith, 2006). In recent years it has been incorporated into water efficient landscapes (Aldridge et al., 2009; Board of Water Supply, 2004; USDA-NRCS, 2007), streambank stabilization (Crago and Puttock, 2008), native species roadside re-vegetation (DeFrank and Lukas, 2012), and buffer strip plantings (A. Fares, personal communication). A major hindrance to the immediate and large-scale use of tanglehead is its seed dormancy. Freshly harvested seeds exhibit poor to no germination. To remove dormancy and improve seed germination, an after-ripening period (i.e., dry storage) of 6 to 12 months is required (Baldos et al., 2014; Daehler and Goergen, 2005; Pater, 1993; Tothill, 1977; USDA-NRCS, 2007). Alternatively, dormancy of tanglehead can be relieved by soaking the seeds in 0.5% (C. Daehler, unpublished data) to 1% gibberellic acid (Tothill, 1977). This practice, however, can be costly and results in elongated seedlings (O.C. Baldos, personal observation). The effects of smoke and aqueous smoke extracts on stimulating seed germination are well known. It has been shown to promote germination in both fire and non-fire-adapted species (Flematti et al., 2013) including a number of crops (Chumpookam et al., 2012; Drewes et al., 1995; Sparg et al., 2006; Taylor and van Staden, 1998; Thomas and van Staden, 1995). It is estimated that 1200 species from 80 genera are smoke-responsive under field conditions (Chiwocha et al., 2009; Dixon et al., 2009; Flematti et al., 2011a, 2013). Recently, two a.i. in smoke responsible for improving seed germination have been isolated and characterized. The butenolide compound, 3-methyl-2H-furo[2,3-c]pyran-2-one or KAR1, was first isolated in 2004. KAR1 was discovered and described in Australia by Flematti et al. (2004) and was later corroborated in South Africa by van Staden et al. (2004). KAR1 is a highly active, heat-stable, and long-lasting compound (van Staden et al., 2004) capable of stimulating germination in lettuce (Lactuca sativa) and in a large number of smoke-responsive species (Flematti et al., 2011a; Nelson et al., 2012). KAR1 is a very potent germination stimulant. Species sensitive to KAR1 can be stimulated to germinate at very low concentrations (1 ppb; 1 mg·L; 10 M) (Flematti et al., 2004, 2013). KAR1 can be isolated from smoke-infused water prepared from the combustion of plant material, cellulose, or simple carbohydrates (Flematti et al., 2011b). A number of synthetic analogs have also been prepared (Flematti et al., 2007; Goddard-Borger et al., 2007; Scaffidi et al., 2011; Sun et al., 2008) with some of these detected in smoke (Chiwocha et al., 2009). Based on combustion experiments with pure xylose, glucose, or cellulose, it was proposed that KAR1 is derived from a pyranose sugar (Flematti et al., 2011b; Nelson et al., 2012). Glyceronitrile is another compound recently isolated from plant-derived smoke. It was first isolated and characterized in 2011 from smoke-infused water prepared from the combustion of oaten (Avena sativa) hay as well as from fresh and dried bushland shoot materials (Flematti et al., 2011a). Research that led to the isolation and characterization of glyceronitrile was spurred by the inactivity of KAR1 on seeds of Anigozanthos manglesii, a smoke-responsive species (Flematti et al., 2011a). Glyceronitrile itself does not cause the observed germination stimulation in A. manglesii seeds. Flematti et al. (2011a) found that, in the presence of water, glyceronitrile slowly hydrolyzes to release cyanide, which HORTSCIENCE VOL. 50(3) MARCH 2015 421 PROPAGATON AND TISSUE CULTURE

hortscience

Germination Response of Dormant Tanglehead (Heteropogon contortus) Seeds to Smoke-infused Water and the Smoke-associated Stimulatory Compounds, Karrikinolide and Cyanide