|Kelsey, R - USDA FS, CORVALLIS, OR|
|Karchesy, J - OSU, CORVALLIS, OR|
Submitted to: Sudden Oak Death Science Symposium
Publication Type: Abstract Only
Publication Acceptance Date: November 1, 2005
Publication Date: March 5, 2007
Citation: Manter, D.K., Kelsey, R.G., Karchesy, J.J. 2007. Photosynthetic declines are induced by Phtophthora ramorum infection and exposure to elicitins. Sudden Oak Death Science Symposium. p. 125. Technical Abstract: Phytophthora ramorum, causal agent of sudden oak death, is responsible for widespread oak mortality in California and Oregon, and has the potential to infect 100 or more species. Symptoms ranging from stem girdling and shoot blight to leaf spotting. In this study, we examined the physiological impacts of P. ramorum infection on Rhododendron macrophyllum. In stem-inoculated plants, photosynthetic capacity (Vcmax) significantly declined by ca. 21% three weeks after inoculation in visibly asymptomatic leaves. By four weeks, after the development of significant stem lesions and loss in water transport capacity, water stress led to stomatal closure and additional declines in photosynthetic capacity. We also report the isolation, characterization and biological activity of two P. ramorum elicitins. Both elicitins were capable of inducing a hypersensitive-like response in one incompatible (Nicotiana tabacum SR1) and three compatible hosts (R. macrophyllum, Lithocarpus densiflorus, and Umbellularia californica. Infiltration of leaves from all three compatible hosts with both P. ramorum elicitins caused significant declines in chlorophyll fluorescence (Fv/Fm). For all four species, the loss of photosynthetic capacity was directly proportional to H+ uptake and ethylene production, two common components of the hypersensitive response. This is the first report of elicitins causing photosynthetic declines in compatible hosts independent of plant water stress.