Note Comparing Estimates of Seed Viability in Three Foxtail (Setaria) Species Using the Imbibed Seed Crush Test with and without Additional Tetrazolium Testing Jaclyn K. Borza, Paula R. Westerman, and Matt Liebman* Estimates of seed viability using the imbibed seed crush test, a method performed by applying pressure to imbibed seeds, were compared with estimates obtained from using the imbibed seed crush test supplemented with tetrazolium staining. The seeds of three weed species, giant foxtail, green foxtail, and yellow foxtail, were collected from three different crops and tested by each method. The results from the two approaches were strongly and significantly correlated. The imbibed seed crush test requires considerably less skill and time to perform and is a reasonable alternative to tetrazolium staining to test the seed viability of newly produced foxtail seeds. Nomenclature: Tetrazolium, 2,3,5 triphenyl tetrazolium chloride; giant foxtail, Setaria faberi Herrm. SETFA; green foxtail, Setaria viridis (L.) Beauv. SETVI; yellow foxtail, Setaria glauca (L.) Beauv. SETLU. Key words: CR, imbibed seed crush test; TZ, tetrazolium test. Seed viability is a critical measure in plant demographics and population dynamics research. Conducting seed-bank surveys and monitoring fluctuations in seed populations require intensive sampling and testing for seed viability on a large scale (Buhler and Hartzler 2001; Menalled et al. 2005; Nurse and DiTommaso 2005). Nonetheless, viability testing for weed seeds has proven especially difficult on account of the small size, the high number of seeds produced from each plant, and the long dormancy times that weed seeds can exhibit. Weed species of the genus Setaria (foxtails) are one such group that poses these challenges when estimating seed viability. For example, seeds of giant foxtail are small (170 mg/100 seeds) (Buhler and Hartzler 2001), are pro- duced abundantly {150 to 330 seeds per plant in corn (Zea mays L.) and 2,200 to 22,222 seeds per plant in soybean [Glycine max (L.) Merr.]} (Bussan et al. 2000), and exhibit physiological dormancy (Dekker 2003). Foxtail species are highly adaptive and widely distributed throughout North America and world agriculture (Dekker 2003). In the midwestern United States, foxtail species constitute an important biological and economic challenge to crop pro- duction (Bridges and Bauman 1992). Seed viability is the capacity of a seed to germinate and produce a normal seedling under favorable conditions. In foxtail species, viable and nonviable seeds can be indistin- guishable in appearance and dormant seeds can remain viable for long periods of time with delayed germination (Fenner 1985; Nurse and DiTommaso 2005). There are multiple methods used for testing seed viability, but these vary in accuracy and time efficiency. Germination rates of seeds in soil flats and petri dishes have been used as measures of viability (Rothrock et al. 1993). This technique is typically performed in a greenhouse or growth chamber under conditions that stimulate germination and may take many months or years to complete. The germination rate does not take into account seeds that can remain dormant even during favorable growing regimes (Fenner 1985). Moreover, seeds that are viable at the beginning of the test may become nonviable at some point during the lengthy study period for reasons such as fungal infection. The tetrazolium staining test is an established method of assessing seed viability that is widely used for official and nonofficial applications (Buhler and Hartzler 2001; ISTA 1985; Nurse and DiTommaso 2005). In this test, a diluted solution of 2,3,5 triphenyl tetrazolium chloride is applied to seeds and upon its penetration into living cells, the salt is reduced to a reddish, water-insoluble compound (ISTA 1985). Following this enzymatic reaction an observer can describe a seed as viable or nonviable from the stained tissues within the seed. The accuracy of the tetrazolium staining test can be superior to other methods but depends largely on the training of the analysts and their understanding of individual embryo structures. This method is laborious and is especially difficult to use on small weed seeds, such as foxtail species, where identification of some embryo components requires substantial magnification. The seed crush test or pressure test is a method used to test viability by visual inspection and the application of pressure with forceps (Buhler et al. 2001; Forcella et al. 1996; Nurse and DiTommaso 2005; Rothrock et al. 1993; Sawma and Mohler 2002). The crush test categorizes nonviable seeds as those that collapse under gentle pressure, whereas viable seeds remain firm following this pressure. This is an accelerated and immediate method of determining seed viability. Sawma and Mohler (2002) performed crush tests on unimbibed seeds for four weed species, common lambsquarter (Chenopodium album L.), redroot pigweed (Amaranthus retroflexus L.), smooth pigweed (Amaranthus hybridus L.), and velvetleaf (Abutilon theophrasti Med.) and found this method was much less laborious than the tetrazolium test. However, they concluded that for all species tested, there was potentially DOI: 10.1614/WT-06-110 * Research Associate, Postdoctoral Researcher, and Professor, Department of Agronomy, Agronomy Hall, Iowa State University, Ames, IA 50011. Corresponding author’s E-mail: jkborza@iastate.edu Weed Technology 2007 21:518–522 518 N Weed Technology 21, April–June 2007