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The primary objective of this study was to investigate the radiosensitivity of Pseudotsuga menziesli (Mirb.) Franco, Douglas-fir, from two different provenances representing the coastal and interior regions in British Columbia, Picea sitchensls (Bong.) Carr., Sitka spruce, and Tsuga heterophylla (Raf.) Sarg., Western hemlock. A secondary objective was to correlate the radiosensitivity with some cytogenetical and biochemical characteristics. Induction of mutations and radiostimulation of seed germination and seedling growth were also sought. Filled seeds of the above mentioned species were given five different dosages of gamma-irradiation from a cobalt-60-source control, 500, 2,000, 5,000, and 10,000 R. Stratification for 14 days at 0°-2°C as post-irradiation treatment was tested. Germination values were evaluated and germinants were transplanted. Survival and growth under controlled environmental conditions were recorded for 182 days. The species exhibited differential responses to seed irradiation. All showed drastic reduction in germination and survival at the higher dosages, (5,000-10,000 R). There was some stimulation of Interior Douglas-fir seed germination and seedling survival at 500 and 2,000 R irradiation dosages over the control. The same exposures stimulated the height growth of Coastal Douglas-Fir. Stratification after irradiation reduced seed germination and seedling growth and survival in all the species. The tolerance to gamma-irradiation decreased in the following Order: Interior Douglas-fir, Coastal Douglas-fir, Western hemlock and Sitka spruce. Sitka spruce had a significantly larger nuclear volume than Western hemlock and Douglas-fir. No correlation was found between nuclear volume, or interphase chromosome volume, and LD₅₀ (germination). The amount of DNA per cell and per chromosome differed significantly among the three species with Sitka spruce having the highest DNA content followed by Western hemlock, Coastal Douglas-fir and Interior Douglas-fir. Significant negative correlations were found between DNA content per cell and per chromosome, and LD₅₀ (germination). This indicated that DNA content plays a more important role than nuclear volume in determining the radiosensitivity of the species. The differences in radiosensitivity, nuclear volume and DNA content between the Coastal and Interior forms of Douglas-fir are discussed in relation to their ecogeographical distribution and taxonomy. Chromosome breaks, micro-nuclei and chromosome erosion were detected in irradiated seeds of Douglas-fir. Intraspecific hybridization was carried out in Douglas-fir using gamma-irradiated pollen grains. Pollen irradiation up to 5,000 R increased the number of filled seeds/cone. Seedlings from pollen irradiated at 500 R, exhibited some increase in height growth. Similar effects were obtained for pollen germination in vitro. The possibilities of utilizing seed and pollen irradiation in forest tree improvement are discussed' and recommendations are made for future mutation breeding work. / Forestry, Faculty of / Graduate

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Following reports that limited gene transfer may be facilitated by making crosses with irradiated pollen, a debate has arisen as to the cause of the observed results. If maternal trends that occurred in the second generation (the M2) were largely due to the persistence of radiation induced damage, then pollen irradiation would be of little value to plant breeders. But if much of the paternal genome had been eliminated, the method could offer breeders a cheap and simple means of transferring just a few characters from one plant genome to another. By carrying out reciprocal irradiated and control crosses, it was shown in this study with barley that mutational damage is not widespread in the M2. However, consistent trends away from the F2 towards the maternal expression were not observed either. When instead the female gamete was irradiated, moderate shifts to the paternal expression did occur. As trends were for increased vigour, mutational damage is unlikely to have been the cause of these observations. By contrast, when irradiated pollen crosses were made between three varieties of potato, the M1 and M2 were consistently lower scoring than the controls. It is suggested that the results may have been different in the two species because polyploids such as the potato may be better able to tolerate radiation damage than diploids such as barley. Gamete irradiation may, therefore, be of little value in polyploid crops. It is recommended that, at least in diploid species, ovule irradiation should be further investigated because not only may it be more effective than its male equivalent, but it may also be easier to perform. Both techniques may be useful in breaking down linkages resistant to conventional crossing.

Buckwheat ( Fagopyrum esculentum ) derives its name from the likeness of the fruit to a beech-nut (German :Buchweizen). It probably originated in the Himalayas (Stoletova, 1940). The earliest record of buckwheat cultivation was found in Germany in an old register dated 1436 (Hill, 1937; Ames, 1939). It is in no way related to wheat except that it has some importance as a "cereal" and is hence called a pseudo-cereal. [...]

Investigations were made of the association among megagametogenesis, pollen morphology, and seed production in two irradiated apple varieties, Golden Delicious and McIntosh, and in two years, 1964 and 1965. In each year eight to ten clones of each variety were selected on the basis of low, medium, and high pollen abortion. Untreated and treated Golden Delicious and McIntosh clones with normal pollen production, approximately 90% and 50% respectively, had the highest proportion of embryo sacs at the differentiated 8-nucleate stage, and the smallest proportion of embryo sacs at the 2- and 4-nucleate stages. Irradiated clones with the least normal pollen had the highest proportion of immature 2- and 4-nucleate embryo sacs. With both varieties and in both years reduced pollen fertility was positively correlated with retarded embryo sac development. Check clones with high pollen fertility had the highest number of developed seeds per fruit and irradiated clones with reduced pollen fertility had the smallest number of developed seeds per fruit. The number of developed seeds per fruit was positively correlated with the proportion of mature 8-nucleate embryo sacs. The reduction in seed numbers in irradiated apple clones with reduced pollen fertility may be explained, in part, by retarded embryo sac development. / Land and Food Systems, Faculty of / Graduate

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