Variation in seed dormancy of tetraploid wheat

In western Canada, durum wheat cultivars, (Triticum durum) have low to moderate levels of seed dormancy and are susceptible to pre-harvest sprouting. The first objective of this research was to evaluate the dormancy level of Canadian durum wheat cultivars and to identify tetraploid wheat accessions with elevated levels of seed dormancy. Level of seed dormancy and length of after-ripening of 17 Canadian durum wheat cultivars and a collection of 78 tetraploid wheat germplasm were evaluated. The plants were grown under field conditions in 1995 and 1996, harvested at maturity (Zadok's Growth Stage 92), dried at room temperature for one week, and assessed for level of seed dormancy over seven weeks of after-ripening. The results indicated that the durum cultivars Kyle, Mindum, Pelissier, and Wascana 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.;Seventy-eight accessions of T. turgidum, T. turanicum, T. carthlicum, T. polonicum, and T. durum from the USDA germplasm collection were evaluated for seed dormancy with the idea of identifying potential breeding materials. At ZGS 92, eighteen accessions were classified as dormant. Accession 93--282 was the only highly dormant genotype (<20% germination) in this study and was the only genotype that had a longer period of dormancy than the durum cultivar, Kyle.;The level of seed dormancy was evaluated for the most promising accessions at five temperatures under controlled conditions. All cultivars with a high level of dormancy at the higher temperatures germinated rapidly at a lower temperature. The dormancy indices of tetraploid accessions 93--62 and 93--177 were 37% higher than that of Kyle.;Variation in seed moisture may influence the persistence of seed dormancy. The dormant accessions had similar rates of water uptake. Sceptre (a non-dormant cultivar) had a higher rate of water uptake than dormant accessions.;Genetic variants for abscisic acid levels are important for investigating the role of ABA in the persistence of seed dormancy. A combined analysis of variance indicated no significant in ABA level among genotypes at maturity. During early stages of germination, the endogenous ABA level in the seed of four wheat genotypes was analyzed. During imbibition a transient increase in ABA level was observed followed by a decline and an increase in the post-12 hour period. These results suggest that during imbibition, wheat grains are able to synthesize ABA.;The ABA levels dropped in all genotypes over seven weeks of after-ripening. A decrease in ABA level during after-ripening could play a role in loss of seed dormancy.;The results of this study showed that Canadian durum cultivars were non-dormant and a number of tetraploid wheat genotypes in the USDA collection were more dormant than the durum cultivars. The accessions selected in this experiment can provide breeding material for the improvement of pre-harvest sprouting. The phenomena of ABA resynthesis in seed during early stages of germination may open a new area to study the role of germination inhibitors in seed dormancy. (Abstract shortened by UMI.)...