variation of seed dormancy and after-ripening in tetraploid wheat (triticum durum, t. turgidum, t. turanicum, t. carthlicum, t. polonicum)

in western canada, durum wheat cultivars (triticum durum) have low to moderate lev-els of seed dormancy and are susceptible to pre-harvest sprouting. the aim of this study was to evaluate the dormancy level of canadian durum wheat cultivars and to identify tetraploid wheat accessions with elevated levels of seed dormancy. first, the level of seed dormancy and length of after-ripening of 17 north american durum wheat cultivars were evaluated. the plants were grown under field conditions in 1995 and 1996, harvested at maturity (zadok’s growth stage 92, zgs 92), dried at room temperature for one week, and assessed for level of seed dormancy over seven weeks of after-ripening at 20c. seed dormancy was characterized by the extent of germination at 20c. the results indicated that five durum cultivars exhibited moderate levels of seed dormancy at maturity while the remaining cultivars were non-dormant. likewise, a rapid loss of dormancy (within 2-3 weeks of after-ripening) was characteristic of all durum cultivars. in a second experiment, 78 accessions of t. turgidum, t. turanicum, t. carthlicum, t. polonicum, and t. durum from the usda germplasm collection grown under field conditions in 1995 and 1996 were evaluated for seed dormancy with the idea of identifying potential sources of increased seed dormancy. at zgs 92, eighteen accessions were classified as dormant. accession 93-282 was the only highly dormant genotype in this study. the seven most dormant acces-sions, identified in two years of field tests, were tested for length of the dormancy period. accession 93-282 was the only genotype that had a longer period of dormancy than the durum cultivar, kyle. the intensity of seed dormancy was quantified at five germination temperatures. a dormancy index was calculated from germination data at 10 and 20°c. the dormancy indices of tetraploid accessions 93-62 and 93-177 were 37% higher than that of the durum cultivar kyle.