Multiple Disease Resistance to Four Leaf Spot Diseases in Winter Wheat Accessions from the USDA National Small Grains Collection

Tan spot (TS, caused by Pyrenophora trit-ici-repentis), Stagonospora nodorum blotch (SNB, caused by Phaeosphaeria nodorum), spot blotch (SB, caused by Cochliobolus sativus), and Septoria tritici blotch (STB, caused by Mycosphaerella graminicola) are important leaf spot diseases of wheat (Triticum aestivum L. subsp. aestivum) worldwide. Most commercial wheat cultivars are often resistant to one pathogen but susceptible to the others. Our objective was to identify resistance to multiple leaf spot diseases in a subset of winter wheat accessions from the core collection of the National Small Grains Collection of the USDA-ARS. In total, 633 winter wheat accessions were evaluated for resistance in a greenhouse and 205, 278, 146, and 68 accessions were resistant to TS, SNB, SB, and STB, respectively. Resistance to STB, SNB, and SB were positively associated, but resistance to TS was positively associated only with STB. Except for STB, resistance was more common among accessions from Europe than accessions from Asia. Cultivars and breeding lines were more likely to be resistant to SNB and STB compared with landraces. Fifty-six accessions were resistant to three or more diseases, and of these, five (CItr16595, PI 278612, PI 351330, PI 361858, and PI 351983) were resistant to all four diseases. On the basis of Germ-plasm Resources Information Network data, 17 of the 56 wheat accessions were resistant to at least two additional diseases. These multiple disease resistance sources will be useful in wheat breeding programs.