Resistance to the Ug99 Race Group of Puccinia graminis f. sp. tritici in Wheat–Intra/intergeneric Hybrid Derivatives

Abstract

New races of Puccinia graminis f. sp. tritici, the causal agent of stem rust, threaten global wheat production. In particular, races belonging to the Ug99 race group significantly contribute to yield loss in several African nations. Genetic resistance remains the most effective means of controlling this disease. A collection of 546 wheat–intra- and intergeneric hybrids developed by W. J. Sando (United States Department of Agriculture, Beltsville, MD) was screened with eight races of P. graminis f. sp. tritici, including races TTKSK, TTKST, TTTSK, TRTTF, TTTTF, TPMKC, RKQQC, and QTHJC. There were 152 accessions resistant to one or more races and 29 accessions resistant to TTKSK, TTKST, and TTTSK. Of these 29 accessions, 9 were resistant to all races, 14 had infection type patterns that were indistinguishable from cultivars possessing Sr9h and Sr42, 2 were indistinguishable from accessions with SrTmp, and 4 did not display resistant patterns of accessions with any known Sr gene. Three accessions (604981, 605286, and 611932) characterized cytogenetically were disomic substitution lines, each with a single Thinopyrum ponticum chromosome pair. One accession (606057) was a disomic substitution or addition line with two pairs of T. ponticum chromosomes. In total, seven accessions are postulated to contain novel stem rust resistance genes. This research indicates the value of extant collections of wheat–intergeneric hybrids as sources of disease resistance genes.