Identification of New Sources of High Levels of Resistance to Dwarf Bunt and Common Bunt among Winter Wheat Landraces in the USDA-ARS National Small Grains Collection

Although seed treatments are available for control of common bunt and dwarf bunt of wheat (Triticum aestivum L. and other Triticum species), host resistance is an important part of cultivar development in many areas of the world. Few resistance genes are used, creating vulnerability to new pathogenic races. Thousands of landraces from the USDA National Small Grains Collection were screened for resistance to common bunt and dwarf bunt race composites. Fifty-five resistant lines were screened with six races of common bunt and three races of dwarf bunt that have characteristics that are useful for elucidating resistance factors. All previously known sources of useful bunt resistance and most of the other lines tested were susceptible to one or more races. Seven lines were identified that were resistant or immune to all of the races indicating the presence of unknown resistance genes. Some wheat versus race interactions indicated unknown resistance genes and also indicated the presence of unknown virulence factors in some of the bunt races. Previously, most resistant lines were identified on the basis of a high level of resistance to composites of pathogenic races. Using bunt races identified various common resistance factors among the lines that will enable the selection of diverse sources of resistance to be used as parents in breeding programs. The seven new lines that were resistant to all the bunt races should be valuable for the introgression of new sources of resistance, broadening the genetic diversity of bunt resistance in cultivars.