- Wheat (Triticum aestivum) is a highly valuable crop that makes up a large portion of the world’s food. However, breeding for improved varieties with desirable characteristics can be a challenge. This research examined two different issues wheat breeders deal with throughout the selection process all the way to production of Certified seed. The first study examined how 39 cultivars as well as 6 experimental crosses differ in grain dormancy expression. In order to see if dormancy has been systematically bred out of soft white winter wheat, the release date of the cultivars used in this trial ranged from 1948 to 2012. The second study investigated the source of phenotypic variation that appeared in Foundation seed fields of the recently released variety Bobtail. Bobtail was bred to be a semi-dwarf awnletted wheat that was superior in productivity and disease resistance. Plants of Bobtail were observed to segregate for awned and awnless phenotypes which also varied in plant height. Since there was variation in plant phenotypes observed in the Foundation seed field, it was important to determine what was causing the plant segregation.
The first study was conducted over the course of two years and in the first year was only planted at Corvallis, OR, while second year trials were planted at Corvallis, OR as well as Pendleton, OR. To investigate how varieties differed in dormancy expression, seed germination trials were conducted at two temperatures in the first year (4°C and 20°C), and four temperatures in the second year (4°C, 10°C, 20°C and 30°C). In the first year, the impact of temperature during seed germination as well as dry storage on the breakdown of grain dormancy expression was investigated; whereas in the second year, the effects of ripening environment and temperature during germination on dormancy expression were determined. First year results demonstrated that soft white winter wheat does not show any grain dormancy at 20°C within the first few weeks after harvest, regardless of the temperature in which the grain was stored or germinated. Results from the second year showed that grain ripening environment has an impact on seed germination rates at different temperatures. A rain event occurred two days prior to harvest at the Corvallis, OR location but not at the Pendleton, OR location. None of the varieties showed any dormancy when they were imbibed at 20°C within 48 hours after harvest. However, some varieties demonstrated high-temperature induced dormancy when they were imbibed and kept at 30°C. This temperature slowed seed germination rate and cultivars that exhibited high-temperature induced dormancy were: Brevor, Bobtail, Cayuga, Gene, Nugaines, Rely and the experimental line 11-225-6H. There was no trend linking older released varieties to higher levels of seed dormancy compared to more recently released varieties, indicating that seed dormancy has not been systematically bred out of soft white winter wheat over time.
For the second study, sixteen heads were snapped from a segregating head row that originated from a Bobtail Foundation seed field (one seed head was lost in the field). The objective of this study was to determine if the phenotypic variation was due to a contamination event or if it was a genetic variant of the variety Bobtail. There were several possibilities that could have caused the phenotypic variation such as an epistatic event, translocations, out-crossing or some type of seed contamination. To determine the source, sixteen plants from each of the fifteen heads collected from the segregating head row were grown in a greenhouse over the course of two generations. DNA samples were taken from all of the plants from the first generation. Eleven markers that showed polymorphism among a diverse panel of wheat varieties from a previous study were used in this trial and seven of the markers showed amplification and success. The results showed that there was very little variation among the individuals in this trial. The greenhouse trial that was grown to observe the plant segregation patterns revealed that the segregating lines segregated at a 3:1 awnless:awned ratio. All plants that came from an awned plant remained awned and several of the lines remained completely awnless. The marker analysis demonstrated there was no source of contamination and that plants observed segregating were a true genetic variant of the variety Bobtail. Phenotypic data showed that complete elimination of awned plants through the breeding and selection process had not occurred. Plants that came from segregating lines followed a typical Medelian segregation ratio. With this information, this variant was added to Bobtail’s variety description since it was not genotypically different.