Physiologic Specialization of Puccinia triticina on Wheat in the United States in 2014.

Collections of Puccinia triticina obtained from wheat fields and breeding plots in the Great Plains, Ohio River Valley, and southeastern states, were tested for virulence in 2014 in order to determine the virulence of the wheat leaf rust pathogen population in the United States. Single uredinial isolates (380 total) were derived from the collections and tested for virulence phenotype on 20 lines of Thatcher wheat that are near-isogenic for leaf rust resistance genes. In 2014, 55 virulence phenotypes were described in the United States. Virulence phenotypes MBTNB, TBBGS, and TCRKG were the three most common phenotypes. Phenotypes MBTNB and TCRKG are both virulent to Lr11, and TCRKG is also virulent to Lr18 and Lr26. MBTNB and TCRKG were most common in the soft red winter wheat region of the southeastern states and the Ohio Valley. Phenotype TBBGS is virulent to Lr39, which is present in the hard red winter wheat cultivars, and Lr21, which is present in the hard red spring wheat cultivars. Isolates with virulence to Lr11, Lr18, and Lr26 were most common in the southeastern states and Ohio Valley region. Isolates with virulence to Lr21 and Lr39 were most common in the hard red wheat region of the southern and northern Great Plains.