Graduate Thesis Or Dissertation
 

The influence of moisture and temperature on the preservation of Douglas-fir pollen by freeze-drying

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  • Forest crop improvement through the application of genetic principles has been recognized as an important factor in forest management. The use of hybridization and selective breeding in forest tree improvement points to the urgency of maintaining "pollen banks" of superior trees. The objective of this study was to determine the influence of moisture and temperature on the longevity of Douglas-fir pollen, and the effectiveness of the freeze-drying technique of cell preservation in an attempt to prolong pollen vitality for at least one year. Three lots of pollen were collected in the spring of 1961 and given pretreatments of non-air-drying, air-drying, and air-drying in combination with prechilling. Following the pretreating of the pollen, batches of each lot were freeze-dried for 0, 30, 60, and 120 minutes after which they were sealed under vacuum in tubes and stored at 20° C, 3° C, and -18° C. Immediately following treatment, and also after storage for one and two years, a sample from each level of freeze-drying and storage temperature was germinated in the laboratory to determine the percentage of viability. Also, the various treatments were applied to isolated ovulate cones to determine the seed-setting capability of the treated pollen. Fresh pollen was also applied to receptive seed cones to provide a basis for comparison. Tests showed that the technique of freeze-drying reduced the viability and the moisture content of Douglas-fir pollen, the degree of reduction in viability depending on the vacuum duration and pretreatment of the pollen. Following two hours treatment, the moisture content was reduced to two percent or lower, while untreated fresh pollen contained 12 percent or higher. There was a proportional reduction in the percentage of viability with increasing vacuum duration; however, a pretreatment of air-drying and prechilling significantly lessened the reduction in viability caused by freeze-drying. Following two hours of freeze-drying after pollen was pretreated in this manner, the viability was still 81 percent of the original viability as compared to 20 and 36 percent for non-air-dried and air-dried pretreatments respectively. Results showed that storage at 3° C (cold room) permitted retention of pollen viability under higher moisture contents than storage at 20° C (room temperature) or -18° C (freezer). Safe storage under the latter temperatures required lower levels of moisture of between two and five percent. Following one years storage, only non-freeze-dried pollen stored at 3° C (cold room) and -l8° C (freezer) was able to produce sound seeds. One year old freeze-dried pollen stored at 3° C, -18°C, and even 20° C was able to produce sound seeds in quantities equivalent to that of fresh pollen when pretreatment included air-drying and prechilling. After two years storage, seed production was also higher among freeze-dried samples than non-freeze-dried samples in all three pollen lots. Seed production with freeze-dried pollen following two years of storage dropped considerably from that after one year; however, some samples showed fertilizing capacity comparable with fresh pollen. In general, the freeze-drying technique proved reasonably successful in prolonging the vitality of Douglas-fir pollen, especially for one year. Freeze-drying periods of one-half and one hour showed satisfactory results, while two hours of treatment tended to reduce pollen viability excessively.
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file details Livingston_Gordon_Kay_1964.pdf 2017-08-14 Público Baixar