Germination Rate at Low Temperature: Rubber Rabbitbrush Population Differences

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Abstract
The concept that low-temperature germination response is a population rather than a species characteristic has implication 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.degree. 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 possibiliity that other important range species might show similar patterns of variation in low-temperature germination response merits investigation.