Screening Gulf Coast forest species for susceptibility to Phytophthora ramorum

Abstract

Phytophthora ramorum, the causal agent of sudden oak death in California oak woodlands, poses a threat to woody plants in the rest of the United States, including the Gulf Coast area, which is regarded as a high-risk location. Several plant species native to Gulf Coast forests were tested for susceptibility to P. ramorum, including yaupon (Ilex vomitoria Aiton), spice bush (Lindera benzoin (L.) Blume), southern magnolia (Magnolia grandiflora L.), sweetbay magnolia (Magnolia virginiana L.), black willow (Salix nigra Marsh.), baldcypress (Taxodium distichum L.), Virginia creeper (Parthenocissus quinquefolia (L.) Planch.) from two sources (Louisiana and Maryland), and eastern baccharis (Baccharis halmifolia L.). This study was conducted at the U.S. Department of Agriculture Agricultural Research Station biosafety containment greenhouse facility at Ft. Detrick, Maryland. Foliage of four plants for each species tested was inoculated with a suspension of 50,000 zoospores per ml until run-off. Inoculated plants were placed in a dew chamber at 20 °C for 5 days. After incubation period, leaf lesion areas were assessed for necrosis. Representative samples of necrosis infection areas were plated on Phytophthora-selective medium to confirm P. ramorum infection. The average percentage of leaf area necrosis was 5.0, 0.2, 8.6, 1.5, 1.1, 0.2, 32.1, 4.9, and 27.9 percent for inoculated baldcypress, black willow, sweetbay magnolia, Virginia creeper (Louisiana and Maryland genotypes), eastern baccharis, southern magnolia, spicebush, and yaupon, respectively; and 4.2, 0.3, 0.3, 3.1, 1.1, 0.4, 0.6, 1.2, and 0.1 percent for non-inoculated control plants, respectively. Comparison of inoculated versus non-inoculated plants showed significant differences (P≤0.05) for yaupon (P=0.0008), southern magnolia (P=0.001), and sweetbay magnolia (P=0.0009).

Parent Publication

• Proceedings of the sudden oak death fifth science symposium

Citation

Preuett, Jason; Collins, Daniel; Luster, Douglas; Widmer, Timothy. 2013. Screening Gulf Coast forest species for susceptibility to Phytophthora ramorum. 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: p. 87.