The importance of understory infection by Phytophthora ramorum as a means of primary disease establishment in Oregon forests

Abstract

Phytophthora ramorum-infested soils have been implicated as a source of primary inoculum in natural ecosystems. Implicit in this pathway is the need for infection of understory vegetation during pathogen establishment, preceding infection of bole hosts. In support of soil dispersal, studies using artificiallyinoculated soils have shown that understory inoculum can infect low-lying foliage of tanoak (Notholithocarpus densiflorus (Hook. & Arn.) Manos, Cannon & S.H. Oh) and California bay laurel (Umbellularia californica (Hook. & Arn.) Nutt.) (Fichtner et al. 2009). The lack of association between sudden oak death (SOD) and roads in Oregon, however, is inconsistent with a soil-mediated, long-distance dispersal mechanism. Regardless, P. ramorum can be recovered from soils at sites treated as part of the SOD eradication program (Goheen et al. 2008), as well as from streams within infested watersheds during all seasons of the year (Sutton et al. 2009). It is unknown to what extent these understory inoculum sources are responsible for establishing new disease foci, posing a risk for the continued spread of P. ramorum in Oregon.

Parent Publication

• Proceedings of the sudden oak death fifth science symposium

Citation

Peterson, E.K. 2013. The importance of understory infection by Phytophthora ramorum as a means of primary disease establishment in Oregon forests. In: Frankel, S.J.; Kliejunas, J.T.; Palmieri, K.M.; Alexander, J.M. tech. coords. Proceedings of the sudden oak death fifth science symposium. Gen. Tech. Rep. PSW-GTR-243. Albany, CA: U.S. Department of Agriculture, Forest Service, Pacific Southwest Research Station: 91-92.