Phytophthora ramorum’s trophic nature suggests that it cannot utilize dead leaf litter in aquatic systems.

Author ,
Date 2011.
Publication Phytopathology 101:S8.
Key Words
AbstractPhytophthora ramorum, cause of Sudden Oak Death, is routinely isolated from waterways using leaf baits, but the nature of its presence in open waters is unknown. It has often been recovered from waterways with no known terrestrial infestation nearby. To test P. ramorum’s capacity to utilize plant litter as a substrate in aquatic systems, we simultaneously exposed freshly picked rhododendron leaves with those killed by drying or freezing in two infested streams. Baits were deployed monthly during peak pathogen activity from January to June in each of two years. P. ramorum was recovered from 62% of fresh leaves, but only 6% and 2% of frozen and dried leaves, respectively. To further characterize P. ramorum’s trophic capacity, we incubated fresh, frozen and dried leaves separately in cups of water inoculated with P. ramorum or P. gonapodyides (an ubiquitous, presumed saprobic resident of open waters), or combined inoculum of both species for 7 days at 16°C. When incubated alone both species colonized all three bait types; however, P. ramorum was isolated more frequently from fresh and frozen leaves, while P. gonapodyides was isolated more frequently from frozen and dry leaves. When incubated together, P. ramorum was isolated more frequently from fresh leaves than P. gonapodyides, while the opposite occurred with frozen and dry leaves. These results indicate that P. ramorum may be limited biologically and ecologically from colonizing litter in aquatic environments.
Full Citation Aram, K. and Rizzo, D.M. 2011. Phytophthora ramorum’s trophic nature suggests that it cannot utilize dead leaf litter in aquatic systems. Phytopathology 101:S8.