VIEW ARTICLE

The Oversummering and Dispersal of Inoculum of Puccinia striiformis in Oregon. Gregory Shaner, Former Research Assistant, Department of Botany and Plant Pathology, Oregon State University, Corvallis 97331. Present address of senior author: Department of Botany and Plant Pathology, Purdue University, Lafayette, Indiana 47907; Robert L. Powelson, Associate Professor, Department of Botany and Plant Pathology, Oregon State University, Corvallis 97331. Phytopathology 63:13-17. Accepted for publication 3 July 1972. DOI: 10.1094/Phyto-63-13.

Stripe rust (Puccinia striiformis) was found on grasses in wheat-growing regions and in adjacent mountains of Oregon during late spring only after the disease was well established on the wheat crop. Disease incidence on these grasses diminished during summer, and approached zero during August. Stripe rust was seen less frequently on grasses in the mountains than on grasses in the wheatland. Most plants of susceptible grass species were free from stripe rust in the field, but became infected when inoculated in the greenhouse. Commercial wheat plantings served as the sources of inoculum for natural infections of wheat in plots located up to 64 km from wheat fields. Urediospores were trapped on rod spore samplers exposed in the field only after stripe rust was well established on the wheat crop. The number of spores trapped followed closely the development of the disease in wheat fields near the traps. Throughout northeastern Oregon, urediospores moved predominantly from west to east. The results suggest that urediospores which infect the fall wheat crop come from rust that oversummers on residual green wheat and grasses within the wheatland.