Illinois bundleflower and showy ticktrefoil are perennial warm-season legumes native to the United States found in prairies, woodland edges, wet meadows, or disturbed areas in 30 and 28 states, respectively (USDA, NRCS, 2010a). Stands of Illinois bundleflower or other legumes grown with switchgrass (Panicum virgatum L.), sideoats grama [Bouteloua curtipendula (Michx.) Torr.], or Indiangrass [Sorghastrum nutans (L.) Nash] had higher forage yield than if grass stands were grown without legumes (Posler et al., 1993). Both Illinois bundleflower and showy ticktrefoil are used for range revegetation or prairie restoration (USDA, NRCS, 2010a), but plant competition has a significant impact on Illinois bundleflower and other native legume stands (Beran et al., 1999, 2000; Dovel et al., 1990). The cultivar Sabine Illinois bundleflower is used in reclaimed mine areas, rangeland, or pastures, providing ecological benefit to areas of Texas worth almost $225,000 (USDA, NRCS, 2010b).
Pea (Pisum sativum L.) seedcoats prevent rapid imbibition, which may damage the embryo (Powell and Matthews, 1978). However, the seedcoat may be multifunctional and can limit electrolyte leakage and subsequent growth of facultative plant pathogenic fungi; water-impermeable “hard” seedcoats are common in many legumes, serve a protective function for the embryo, and have been the subject of several reviews (Baskin, 2003; Kelly et al., 1992; Mohamed-Yasseen et al., 1994; Rolston, 1978). Latting (1961) determined that mechanical scarification of Illinois bundleflower seed resulted in higher final germination percentage (FGP) compared with sulfuric acid scarification, alternate freezing and thawing, hot water, or control treatments. Mean germination time of 3- or 4-year-stored Illinois bundleflower seed decreased when acid or mechanical scarification was used (Call, 1985). Mechanical scarification of prostrate bundleflower [Desmanthus virgatus (L.) Willd. var. depressus (Humb. & Bonpl. ex Willd.) Turner] seed resulted in higher FGP at a variety of temperatures (Fulbright and Flenniken, 1987).
Dormancy of Illinois bundleflower is the result of a hard seedcoat and abrasion of individual seed with a razor blade or knife is more effective than sulfuric acid soaks at achieving high FGP (Call, 1985; Latting, 1961). There are few publications regarding scarification of showy ticktrefoil seed, although concentrated sulphuric acid soaks are recommended to break dormancy of D. intortum (Mill.) Urb. and D. uncinatum (Jacq.) DC. (ISTA, 2010). General recommendations suggest scarification of Illinois bundleflower and showy ticktrefoil seed before field sowing (USDA, NRCS, 2010a).
Scarifiers have been used to alleviate dormancy in Ruby Valley pointvetch (Oxytropis riparia Litv.; Hicks et al., 1989) and mastic tree (Pistacia lentiscus L.; Piotto, 1995). Varying scarification durations of 5 to 30 s were required for different seed lots of Ruby Valley pointvetch, a legume, for optimum germination (Hicks et al., 1989). Scarifier (Forsberg, Thief River Falls, MN) equipment is simple to operate and consists of a horizontally mounted rotary propeller within a steel drum lined with 40-grit sandpaper (Liu, 2007). Although mechanical abrasion by using the scarifier is a low-cost method with good repeatability, there is a lack of methodological standardization, including running time, seed moisture content, amount of surface damage, and reference materials (Liu, 2008). Mechanical scarification using a scarifier is a more practical method of scarification than other techniques (Hicks et al., 1989).
Vigor tests are more accurate in determining field crop performance of a seed lot than standard germination tests and their use has increased as a result of consumer demand (Ferguson, 1993). Vigor is a concern to growers because a loss of vigor may indicate a reduction in field performance (Copeland and McDonald, 2001). Contemporary standards use electrical conductivity (EC) and accelerated aging for determining seed vigor (ISTA, 2010); however, seed companies use a variety of vigor-testing methods (Copeland and McDonald, 2001). Imbibitional damage of pea cotyledons resulted in higher EC of leachate when the seedcoat was removed, indicating a relationship between “intactness” of the seedcoat and embryo health (Powell and Matthews, 1978). In studies involving soybean [Glycine max (L.) Merr.], germination percentage of seed subjected to accelerated aging procedures was used to determine seed vigor (Baskin, 1977).
At present, there is no established, rapid mechanical seed scarification method for native legumes such as Illinois bundleflower or showy ticktrefoil. The objective of this study was to determine the influence of mechanical scarification using a Forsberg sandpaper-lined electric scarifier on seed germination and vigor of Illinois bundleflower and showy ticktrefoil.
AOSA 2007a Suggested purity and/or germination testing methods for species without Association of Official Seed Analysts Rules testing procedures Assn. of Offic. Seed Analysts 20 Jan. 2010 <http://www.aosaseed.com>.
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Dovel, R.L., Hussey, M.A. & Holt, E.C. 1990 Establishment and survival of Illinois bundleflower interseeded into an established kleingrass pasture J. Range Manage. 43 153 156
Fulbright, T.E. & Flenniken, K.S. 1987 Temperature and scarification effects on germination of prostrate bundleflower seeds J. Range Manage. 40 170 173
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Liu, K. 2007 Laboratory methods to remove surface layers from cereal grains using a seed scarifier and comparison with a barley pearler Cereal Chem. 84 407 414
Liu, K. 2008 Measurement of wheat hardness by seed scarifier and barley pearler and comparison with a single-kernal characterization system Cereal Chem. 85 165 173
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Olszewski, M.W., Pill, W.G., Scheiblin, D.A. & Czymmek, K.J. 2009 Use of confocal microscopy to relate germination vigour to embryo morphology of dormant and non-dormant purpletop (Tridens flavus) Seed Sci. Technol. 37 52 58
Piotto, B. 1995 Influence of scarification and prechilling on the germination of seeds of Pistacia lentiscus Seed Sci. Technol. 23 659 663
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Susko, D. 2008 Seed germination for breaking dormancy in showy ticktrefoil (Desmodium canadense) 35th Annu. Natural Areas Conf Nashville, TN 14–17 Oct (abstr.).
USDA, NRCS 2010b ‘Sabine’ Illinois bundleflower (Desmanthus illinoensis) 17 Feb. 2010 <http://plant-materials.nrcs.usda.gov/news/features/great_am_plant/sabine.html>.
Wang, Y.R., Yu, L., Nan, Z.B. & Liu, Y.L. 2004 Vigor tests used to rank seed lot quality and predict field emergence in four forage species Crop Sci. 44 535 541