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Jointed Goatgrass Seed Dormancy Varies by Region on the Spike

Ted L. Carpenter and Donald C. Thill
1992 Proc. West Soc. Weed Sci. 45: 120


Abstract. Jointed goatgrass (designated a noxious weed in eight states) is increasingly troublesome in Idaho and Washington winter wheat fields, especially in winter wheat seed production fields. Jointed goatgrass spikelets cannot be separated from wheat seed efficiently, due to the similar size of jointed goatgrass spikelets and wheat grain. Because it is related closely to wheat, no currently available herbicide selectively controls this weed in wheat. Seed dormancy allows a small percentage of buried jointed goatgrass seed to remain viable for at least 5 yr in dry areas of Pacific Northwest. The conditions that produce extended dormancy in some jointed goatgrass seed are unknown. Experiments were initiated to determine relationships between dormancy and seed development factors such as, environment influencing the mother plant, spikelet region on the spike, and seed position within the spikelet. Seed from a single accession were planted near Pullman, WA and Lind, WA in 1989. Entire spikes were hand-harvested in 1990, separated by spikelet position (1 through 15), and stored at -18 C. Spikelet positions one through three were grouped as lower region, four through six as middle region, and seven through terminal as upper region. Individual seed (from spikelets containing exactly two seed in the lowermost positions only) were removed and stored. The basal and second position seed were subjected to 30-day germination tests. Seed were placed in petri dishes in a germination chamber maintained at 15 C and 24 hr darkness. Germinated seed were counted and removed daily. The experiment was arranged as a randomized complete block split-plot design (repeated) with four replications, two sites, three regions on the spike, and two seed positions within the spikelet.  Mean percent viability was 99.75%. Seed that did not germinate within the 30-day tests were subjected to a tetrazolium chloride test for viability. Dormancy results of basal seed data are reported, because all second position seed germinated within 14 days. Data were subjected to analysis of variance (ANOVA) which showed that experiments could be combined for analyses of dormancy as a dependent viable. Differences by region on the spike were highly significant (p=.001). Site by region interactions also were significant (p=.001). Seed from the middle of the spikelet were the most dormant in spikes from both sites. Dormancy percentages for Lind-grown seed were 17.5%, 40.5%, and 38.9% for lower, middle, and upper spike regions, respectively. Dormancy percentages for Pullman-grown seed were 33.2%, 43%, and 32% for lower, middle, and upper spike regions respectively.