Jennifer Baker and Dr. Phil S. Allen, Zoology
In order to achieve successful seedling establishment, seeds must have mechanisms to protect against germinating under harmful environmental conditions. One such mechanism, semi-dormancy, can be triggered by dehydration of imbibed seeds. Depending on the length, severity, and extent of hydration prior to dehydration, some seeds exhibit delayed and asynchronous radical emergence upon rehydration.1 The purpose of this project was to further investigate the semi-dormant state in Bromus Btectorum. Btectorum seeds collected in 1995 from Hobble Creek, Utah (BT 1 8) and Strawberry, Utah (BT28) were exposed to dehydration after 18 hours (late) or 10 hours (early) of hydration. Seeds were dehydrated over saturated salt solutions of 32% or 11% humidity for 24 hours or two weeks at 20C. Immediately following dehydration, seeds were rehydrated and germination was scored. 1,2 All hydration and germination occurred at 25C. In contrast to earlier studies, seeds did not show a dramatic delay or asynchronous patterns of germination indicative of semi-dormancy.1 In the previous studies, early dehydration (early in imbibition) resulted in accumulation of time seeds were hydrated, thus resulting in faster germination. In this study, seeds dehydrated early did not accumulate, but rather erased the previous episode of hydration; it required about the same amount of time for the seeds to germinate as the control. Late dehydration (just prior to radicle emergence) affected the seeds more noticeably with slightly delayed and asynchronous germination. These results suggest a difference between the 1995 and the previously used 1992 seed lots. In general, the dehydration severity (humidity) did not have a significant effect.
Temperature, severity, and timing of dehydration interact to determine the rate of dehydration. The more harsh the treatment, or closer to radicle emergence, the greater the effect. However, the semi-dormant state was not observed and the differences between the experimental seed and the control was not as dramatic as was expected. The mechanism by which B tectorum becomes completely dormant in the field is still not thoroughly understood. It is probable that a series of complex events, instead of one wetting and drying episode, interact to induce this state.
References
- Debaene-Gill, S. B., et al. (1994) Journal of Experimental Botany 45(278), 13 01-13 07.
- Allen, P. S., et al. (1994) pp. 215-219. In: Proceedings- -Ecology and Management of Annual Rangelands.
- Special thanks to Dr. Susan E. Meyer of the USDA Forest Service for the use of facilities and her helpful input.