First Report of Rust Caused by Puccinia emaculata on Switchgrass in Arkansas

In May 2007, switchgrass (Panicum virgatum L.) cv. Alamo and a breeding line, OSU-NSL 2001-1, were planted at the Arkansas Agricultural Research and Extension Center, Fayetteville. In August 2008, a high incidence of dark brown-to-black rectangular foliar lesions delineated by major veins was observed throughout plots of both lines. Lesions covered 25% to nearly 100% of total leaf tissue. Similar symptoms were also observed on unknown switchgrass cultivars in Benton County in northwest Arkansas and in St. Francis County in east-central Arkansas, suggesting that the disease was widely distributed throughout the state. The pathogen produced epiphyllous and adaxial masses of dark brown-to-black telia from erumpent fissures on leaf surfaces. Dark brown teliospores were observed under magnification and were two-celled, oblong to ellipsoid, and 33 ± 3.5 μm long with an apical cell width of 17.5 ± 2.7 μm and basal cell width of 16.2 ± 2.8 μm (reported as mean ± standard deviation, n = 25). Pedicles were colorles...