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Proceedings of Past Forest Nursery Association Meetings:

Rocky Mountain Juniper Study: Preliminary Results
Barbour, Jill
1999: Ames, IA
KEY WORDS
Seed treatment, seed germination, seed testing

INTRODUCTION
Rocky Mountain juniper (Juniperus scopulorum Sarg.) seed are hard to germinate in the nursery, containers, or laboratory because they have multiple dormancies. The seedcoat and prophylactic sheath surrounding the embryo impede water absorption. The embryo’s epicotyl is not dormant; only the hypocotyl displays dormancy and requires cold stratification (Djavanshir and Fechner 1976).

Stratification of dormant seed involves three stages (Nikolaeva 1969). During the first stage an initial vigorous swelling of seed take place. Following full imbibition the second stage ensues. Enzymatic activity and hydrolysis of proteins and fats begins. Products from the hydrolytic process prompt the beginning of embryo growth, which constitutes the third stage. Growth activation occurs during stratification in two periods. Mitoses occurs at the end of warm stratification when seed open; whereas, the second activation of growth happens at the end of cold stratification, prior to germination.

This leads to a perennial nursery problem because germination cannot always be predicted. Weather patterns are not identical in every nursery that grows Rocky Mountain juniper. Southernmost nurseries may not receive enough cold weather to provide a sufficient cold stratification period for seed germination. In years when snowfall is not adequate to cover the beds, the seed dry out due to cold, dry, winter winds. Generally, outdoor stratification is not as efficient as constant temperature and moist laboratory stratification, except under conditions of continuous snow cover (Young and Evans 1976). When the seed dry out, they go into secondary dormancy, thereby inhibiting germination.

Multiple stratification regimes make it difficult to manage the seed sown in nursery beds. Past experience among nursery managers has shown that Rocky Mountain juniper seed germinate most uniformly when a warm stratification period precedes the cold stratification period (Meines 1965). Most nurseries plant the seed in July to provide for the warm stratification period. USDA Forest Service Bessey Nursery in Halsey, NE provides the seed an additional 6 months of cold stratification prior to summer sowing (Benson 1976). Summer sowing is not consistent or predictable, because so many things can go wrong before the seed germinate next spring.

At present, there is not a repeatable germination test that can be used to sow seed. An official laboratory germination procedure has not been established. Many of the seed have been found to be empty or to have low viability, which yields inconsistent laboratory results. A tetrazolium test is used as a substitute for germination tests, because it can be performed on the seed in a couple of days. The test measures seed viability but does not predict germination.
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