Abstract:
The Oregon State Cooperative Seed laboratory uses two methods for testing the quality of Douglas-fir seed lots. The first of these is a straight-forward germination test without any pre-treatment of the seed, involving a period of 42 days in the germinator at alternating 20°C.-30°C. temperatures. The second method consists of 14 days pre-chill of the seed on the moistened medium at 5°C. prior to 28 days germination at the same alternating temperatures. The pre-chill helps to overcome dormancy which may be present in the lots. Recent work by several investigators has indicated that soaking pre-treatments might also be employed to overcome dormancy in coniferous seed.
The study was designed to evaluate some of these soaking treatments in relation to the methods at present used by the laboratory. In all cases soaking was followed by pre-chilling; so that a measure of additional effects of the soaking treatment on the dormant seed was obtained. Two studies were made with the normal laboratory testing methods as controls.
The first consisted of soaking the seed in water at temperatures of 5°C., 20°C. and 30°C. for periods of 12, 24, 36 and 48 hours, prior to pre-chill and germination.
In the second study soaking temperatures of 5°C. for 36 hours and 30°C. for 14 hours were used. The seed was soaked in water and in 0.2 percent potassium nitrate solution , to determine the merits of the two soaking media. At 5°C. the effect of light during the soaking was examined together with its effect during pre-chilling on the germination of seed soaked at both temperatures.
Included in the thesis are the results of a small study designed to determine an effective and reliable method of estimating moisture content in the soaked seed. Consequently moisture content was determined on an over-dry weight basis after heating the soaked seed at 100°C. for six hours in an air-oven.
Three seed lots were used in an attempt to obtain results over a wide range of seed quality. As demonstrated by the germination figures, the lots chosen exhibited such a range. Though the lots responded differently to the treatments employed, no over-all increase in germination of the dormant seed present was obtained with any of the treatments. The 30°C. soaking for the longer periods produced a considerable decline in the germination, germinative capacity and germinative energy of the lots.
Dormancy was present in two of the three lots, but the number of dormant seeds remained approximately constant over all the treatments. Dormancy was reduced only in the case of the pre-chilled controls over the controls without pre-chill. The statistical analysis of the germination percentages revealed that temperatures of soaking was the dominant factor affecting germination. The period of soaking, though influencing the moisture content attained, was of little consequence in germination. No responses were obtained with the use of light during soaking and pre-chill, nor with the variation in soaking medium. A convariance analysis of moisture content attained and subsequent germination, indicated the absence of any correlation between the two entities.
Taken as a whole, soaking procedures are of no advantage over the present germination techniques in use at the Oregon State Laboratory for Douglas-fir tree seed.
