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The germination of seeds of beardless and bluebunch wheatgrasses was investigated over a wide range of constant and alternating temperatures. Seeds of ‘Whitmar’ beardless wheatgrass, a collection from Nevada, and numbered accessions of bluebunch wheatgrass were used. Seeds of ‘Whitmar’ beardless wheatgrass germinated at 87% of the 55 temperature regimes tested with a mean germination of 52%. Germination at 42% of the temperature regimes was optimum [defined as not significantly (P = 0.01) different from maximum], with a mean of 84%. Freshly harvested seeds of the Nevada source of bluebunch wheatgrass germinated at 78% of the temperature regimes with a mean of 40%. Comparable figures for fully ripened seeds 5 months after harvest were 84% with a mean of 62%. The germination response of l-month old bluebunch wheatgrass seeds indicated that germination could occur at the high seedbed temperatures encountered in a late summer moisture event. The temperature-germination profiles for the numbered accessions of bluebunch wheatgrass had the same general pattern as the Nevada source. Generally, seeds were highly germinable at a number of temperatures. Optimum germination of all the sources of seed occurred at 37 temperature regimes at least once and always occurred at 15 temperatures ranging from an alternating 5/15’ C through a constant 25” C. This range of germination temperatures is much wider than that exhibited by squirreltail and Sandberg bluebunch. The bluebunch wheatgrass material has the inherent potential to germinate and to be highly germinable at a wide range of temperatures. Bluebunch wheatgrass (Agropyron spicatum) is one of the most widespread and important native forage grasses on rangelands of the western United States (Hitchcock 1951). Bluebunch wheatgrass is the dominant or codominant perennial grass of sagebrush (Artemisia)/ bunchgrass communities in eastern Washington, Idaho, eastern Oregon, northern Nevada, and Utah (Stoddard 194 1, Daubenmire 1970). Considering its wide distribution and the characteristics of other species of Agropyron, bluebunch wheatgrass is not a highly variable species (Hitchcock et al. 1969). Generally, awned and awnless forms are recognized. The awnless phase has been generally recognized in the commercial seed trade and range literature as beardless wheatgrass (Agropyron inerme). Cytogentic evidence shows the two phases to be completely interfertile with normal pairing in meiosis (Cronquist et al. 1977). Understanding the germination ecology of bluebunch and beardless wheatgrasses is vitally important for cultivar selection, management of native stands, and artificial revegetation of degraded stands. One aspect of the germination of these wheatgrass species is their response to temperature. Our purpose was to evaluate the germination of a broad spectrum of wheatgrass collections in response to constant and alternating incubation temperatures. The authors are range scientists, U.S. Dep. Agr., Sci. and Educ. Admin., Agr. Res., Renewable Resource Center, 920 Valley Road. Univ. of Nevada, Reno, 89512. This research is the result of cooperative investigations of the U.S. Dep. Agr., Sci. and Educ. Admin.-Agr. Res. and the Agr. Exp. Sta., Univ. of Nevada, Reno, Journal Series No. 444. a4 Materials and Methods We used seeds of beardless wheatgrass, cultivar ‘Whitmar’ obtained from the Soil Conservation Service (SCS) U.S. Department of Agriculture (Table 1). A total of 10 sources of bluebunch wheatgrass were tested, nine from the SCS, and one from Nevada. The material obtained from the SCS represents the accessions in their collections under evaluation for selection of a cultivar. Accession P-285272 is considered a hybrid of beardless and bluebunch wheatgrass. The source from Nevada was collected from a native stand on the Goldbanks allotment south of Winnemucca, Humboldt County, Nevada. The accessions obtained from the SCS differed in the location at which they were grown, Pullman, Washington, or Bridger, Montana; and the year grown, 1968 to 1976 (Table 1). All SCS accessions were tested in 1978. The Nevada material was grown in a space planted common garden at Reno, Nevada. The garden was given weed control and supplemental irrigation. It was established with seedlings transplanted from the greenhouse in 1977. A limited number of seeds were collected from the plants in 1977 but seed production was excellent in 1978. All germination experiments involved four replications of 25 seeds each and tests were repeated at least once. Seeds were placed on a single thickness of germination paper in petri dishes and kept moist with tap water. Tests were conducted in the dark. Seeds were incubated for 4 weeks with germination counts made weekly. Seeds from all sources were initially tested at constant incubation temperatures of 2,5, 10, 15,20,25, and 30” C. Based on the results of these initial experiments, we selected ‘Whitmar’, the Nevada material, P-6409, P-737, P-739, P-285272, and M-883 for additional testing to develop complete germination profiles. For development of germination profiles, seeds of the selected sources were incubated at constant temperatures of 0,2,5, 10, 15, 20, 25, 30, 35, and 40” C. Alternating temperature regimes consisted of 16 hours at each lower constant temperature and 8 hours at all possible higher temperatures in each 24-hour period. For example, 0” C was alternated with 2, 5, 10, 15, 20, 25, 30,35, and 40” C whereas 35” C was alternated with 40” C only. In all, 55 constant and alternating temperature regimes were tested. In 1978 we tested the Nevada source seed 1 month after harvest and again 5 months after harvest to test for afterripening requirements. After germination data were obtained for all 55 temperature regimes, the percentage of temperature regimes and mean germination for those temperatures that produced some germination were obtained. We define optimum germination percentages as those not significantly different (P = 0.01) from the maximum. The number and mean of the optimums were calculated for each profile. The percent of temperature regimes having germination in the percentiles < 10, 10 to 25 (not including 25), 25 to 50,50 to 75,75 to 90 and >90% was calculated for each germination profile. We compared the temperature-germination profiles of the selections tested under a descriminate classification of seedbed temperJOURNAL OF RANGE MANAGEMENT 34(2), March 1981 Table 1. Species, accession, cultivar, or collection and origin of seeds of wheatgrasses used in germination experiments.’ Species or forma Accession, cultivar, or collection Agropyron inerme Agropyron spicatum Agropyron spicatum Agropyron spicatum Agropyron spicatum A&-obyron spicatum Agropyron spicatum X A. inerme Agropyron spicatum Agropyron spicatum Agropyron spicatum Agropyron spicatum ‘Whitmar’ P-6409 P-737 P-739 P15623 P15634 P-285272 M-883 C-29 Nevada P15649 Origin Union County, Oreg. Lewiston, Idaho Joel, Idaho Asotin, Wash. Granite County, Mont. Park County, Wyo. Tag Germination germination profiles Year grown Location grown (%) developed 76 Union, Oreg. 81 X 76 Pullman, Wash. 81 X 75 Pullman, Wash. 80 X 75 Pullman, Wash. 86 X 68 Bridger, Mont. 67 68 Bridger, Mont. 42 Whitman County, Wash. Wheatland County, Mont. Grand County, Colo. Humboldt County, Nev. Lincoln County, Mont. 71 Bridger, Mont. X 74 Bridger, Mont. X 70 Bridger, Mont. 77-78 Reno, Nev. X 75 Bridger, Mont. ‘Year grown and tag germination taken from seed tag. Not all lots had germination indicated. atures. This classification system included 19 moderate temperature regimes, 5/ 15, (5O C for 16 hr and 15’ C for 8 hr in each day) 5/20, 5/25, lo/ 10 through 10/30, IS/ 15 through 15/35, 20/20 through 20/35,25/ 25/ and 25/ 30” C; 1 I colder than moderate regimes, O/O through O/ 15,2/2 through 2/ 15,5/5and 5/ 100 C; 16 widely fluctuating regimes, O/20 through O/40, 2/20 through 2/40, 5/30 through 5/40, lo/35 and 10/40, and 15/400 C; and 9 warmer-than-moderate regimes 20/ 40, 25/ 35, 25/ 40, 30/ 30 through 30/40, 35/35, 35/40, and 40/400 C. This classification is based on the monitoring of field seedbeds in sagebrush grassland (Evans et al. 1970) and experience with the germination response of many grass species. fluctuating temperature regimes of O/40, 2/40, and 5/40“ C, and the very warm incubation temperature of 40” C. A frequency analysis was used to determine, for all sources of bluebunch wheatgrass, which temperature regimes supported germination most frequently in the optimum range. The inherent ability to germinate at low temperatures while soil moisture is still available is one of the most important germination characteristics influencing seedling establishment in the spring on sagebrush rangelands (Evans et al. 1970). Differences of a few days may mean the difference between successful establishment and seeding failure. ‘Whitmar’ seeds germinated after 4 weeks incubation at O/20” C at a level significantly (P = 0.01) lower from the optimum. However, even this is a fairly high day temperature for field seedbeds in the early spring (Evans et al. 1970). A O/ 15” C temperature regime probably better reflects field conditions. At this regime ‘Whitmar’seed germination fell to 32% and at O/ lo” C it was only 3% (Table 3). Raising the cold period temperature to 2’ C did not significantly increase the germination with warm-period temperatures 15, 20, or 25’ C. Results Screening of Seed from All Sources Comparison of the germination at constant temperatures of bluebunch and beardless wheatgrass seeds from the various sources revealed three lots, P-15634, C-29, and P-15623, that were significantly less germinable than the rest (Table 2). These three accessions were the oldest seeds tested and apparently had largely lost their germinability; two accessions had previously much higher germination percentages, indicated by their lot tags (Table I). These three accessions were dropped from further testing. With cold-period te

Temperature Profiles for Germination of Bluebunch and Beardless Wheatgrasses