Genetics of leaf rust resistance in the soft red winter wheat ‘Caldwell’
The soft red winter wheat (Triticum aestivum L.) ‘Caldwell’ has effective resistance to leaf rust caused by Puccinia triticina. To determine the genetic basis of this resistance, Caldwell was crossed with the leaf rust–susceptible spring wheat ‘Thatcher’, and the F1 plants were backcrossed to Thatcher to obtain backcross (BC) F2 (BC1F2) families. In the seedlings, the BC1F2 families segregated for a single gene to P. triticina race SBDG, which is likely Lr14a based on tests with BC1F3 lines. In field tests, the BC1F2 families segregated for a single gene for adult plant resistance that was independent of the seedling resistance. BC1F2 adult plants were inoculated in greenhouse tests with P. triticina races BBBD and THBJ, and resistant plants were selected and advanced by single-seed descent to produce BC1F4 lines. In greenhouse tests, adult plants of some of the BC1F4 lines had the same low and high infection type (IT) to different P. triticina races as the Thatcher isoline with Lr12. Other BC1F4 plants had intermediate IT to the P. triticina race THBJ. The BC1F4 plants with the intermediate ITs were selected and tested as BC1F5 adult plants in greenhouse tests and as BC1F4:6 lines in field plot tests at two locations. Caldwell likely has the seedling resistance Lr14a, the adult plant gene Lr12, and an uncharacterized adult plant resistance gene that conditions an intermediate level of effective resistance in field plots.