Integrated management techniques for several U.S. winter wheat production regions have been proposed for jointed goatgrass control. These strategies may be improved by a greater understanding of the genetic and environmental influences on seed production and germination. Plants from six jointed goatgrass collections were grown in common garden nurseries at two Oregon locations over two growing seasons. Unbroken spikes from each collection were used to evaluate seed dormancy and quantify seed production by inflorescence position. Germination tests were conducted over 14 d using spikelets of dormant and after-ripened samples in growth chambers set to 25/15 C day/night temperatures and a 12-h photoperiod. Spikelet position on the spike affected germination of the secondary seed in dormant samples of jointed goatgrass Collections D and G. In contrast, spikelet position did not affect secondary seed germination in dormant samples of Collection B. Spikelet position did not influence secondary seed germination in nondormant samples of all three collections. Spikelet position affected germination of the primary positioned seed in dormant samples of Collection B, and in nondormant samples of Collections B, E, and H. Unbroken spikes from jointed goatgrass Collections B and D were used to quantify seed production per spikelet position on the spike and per floret position within the spikelet. Seed production by floret position depended on spikelet position on the spike. This relationship varied for spikes of different lengths and for samples from the two collections. Efforts to model the life history of jointed goatgrass and predict germination should be adjusted to account for floret position within the spikelet, spikelet position within the spike, and source population. We suggest that future dormancy and germination research include sampling seed from several weed populations and efforts be made to standardize germination tests according to seed position on the inflorescence.
Nomenclature: Jointed goatgrass, Aegilops cylindrica Host AEGCY.