Abstract
Wheat stripe rust, caused by Puccinia striiformis f.sp tritici (Pst), can be a highly destructive disease, resulting in significant yield losses in the Pacific Northwest in epidemic years. Brundage, a top-quality, high-yielding, soft white winter wheat variety has been superseded in the last five years due to its susceptibility to the disease. Because of climate conditions in this region, infection by Pst is common. Therefore, introgression of one or more Pst resistance genes into regionally adapted genetic backgrounds is highly desirable. The goals of the present study were, firstly, to establish a tissue culture and genetic transformation system for two regionally adapted varieties: Brundage and UI Platinum. Secondly, to use genetic transformation to improve stripe rust resistance in Brundage. Six wheat varieties were initially tested for the tissue culture response of immature embryos in order to determine their regenerability into whole plants. The results indicated that there were two related groups in regard to regeneration; Fielder, Florida 303, and UI Platinum had similar but higher regeneration capacities than Florida 301, Florida 302, and Brundage. Fielder and UI Platinum are spring varieties, Florida 301 and 303 are facultative, and Florida 302 and Brundage are winter types. The shoot regeneration rate mean was highest for Fielder at 51.72% and lowest for Brundage at 9.90%. Five of aforementioned genotypes, excepting UI Platinum, were used in biolistic bombardment with the Yr28 gene, which is derived from Aegilops tauschii and confers all-stage resistance to stripe rust. There was no significant difference in the transformation rate of each genotype. The Fielder genotype had the highest mean transformation rate at 0.43% with a total of four transformed plants produced from 1,009 embryogenic calli, and Florida 301 had the lowest mean transformation rate at 0.13%, with one transformed plant produced from 952 embryogenic calli. However, the most successful replicate, KJ3, was completed with the Brundage genotype and had a transformation rate of 1.54% with three transformed plants produced from 195 embryogenic calli. Fifteen of the 33 replicates completed produced no plants whatsoever, and eight replicates produced plants, but those plants did not test positive for the for the Yr28 transgene. In total, 24 transformed plants were produced, 11 of which were from the Brundage genetic background, four from Fielder and Florida 302 respectively, three from Florida 301, and one from Florida 303. Ten of the T0 transformed plants showed distinctively resistant phenotypes, six of which were from the Brundage background. Lines carried to the T1 generation displayed genetic segregation for the Yr28 transgene. Some T1 plants were associated with stripe rust resistance. All wheat genotypes selected for transformation were confirmed to be susceptible to the currently prevalent Pst races. The insertion of Yr28, or other Pst-resistance genes, is highly desirable to impart disease resistance in wheat that is otherwise limited in this regard. The current study illustrated that unexploited genes from wild wheat relatives can be harnessed for wheat improvement.