• Germination of downy brome from southern Kansas, central Oklahoma, and north Texas

      Milby, T. H.; Johnson, F. L. (Society for Range Management, 1987-11-01)
      Mature downy brome (Bromus tectorum L.) seeds collected in Texas, Oklahoma, and Kansas in mid-June did not germinate at summer temperatures even when supplied with adequate moisture. The after-ripening of seeds for 3 months produces germination of 50% or more in most populations, as does subjecting fresh seeds to November temperature regimes. These results are similar to those reported for downy brome seeds from eastern Washington, central Idaho, and central California in which fresh seeds are dormant. They differ from those reported for seeds from Montana, northern California, northern and western Nevada, southern Idaho, and northern Utah in which fresh seeds germinate at high percentages. Dormancy of fresh seeds from the Southern Great Plains delays downy brome germination until the fall season at which time rainfall and other climatic conditions are more favorable for its survival.
    • Germination rate at low temperature: rubber rabbitbrush population differences

      McArthur, E. D.; Meyer, S. E.; Weber, D. J. (Society for Range Management, 1987-11-01)
      The concept that low-temperature germination response is a population rather than a species characteristic has implications for range seeding. The success of a seeding could depend on the ability of the seed source to associate the appropriate degree of risk with germination in the cold at a particular site. Germination rate at 3 degrees C was determined for 27 seed collections of rubber rabbitbrush (Chrysothamnus nauseosus [Pall.] Britt) belonging to 9 subspecies and collected in 5 states. Marked differences in low-temperature germination rate were observed. Relative percentage of germination at 14 days varied from 0.4 to 100, while the period required to reach 50% relative germination varied from 5 to 96 days. Germination rate was negatively correlated with a climatic index of winter frost risk to seedlings at the site and seed origin. Warm desert collections germinated fastest, while montane and high latitude collections germinated slowest. Many collections from mid-elevation sites showed the bet-hedging strategy of asynchronous germination in the cold. Germination rate was not correlated with subspecific identity. Subspecies of wide ecological amplitude showed nearly the whole range of germination rate response. The possibility that other important range species might show similar patterns of variation in low-temperature germination response merits investigation.