Host plants of Phytophthora ramorum
In the US, Phytophthora ramorum (EPPO Alert List) has so far been reported on Lithocarpus densiflorus (tan oak), Quercus agrifolia (coast live oak), Q. kellogii (black oak), Q. parvula var. shrevei. It was found on Vaccinium ovatum causing twig dieback, and was isolated from Acer macrophyllus, Aesculus californica, Arbutus menziesii, Arctostaphylos manzanita, Heteromeles arbutifolia, Lonicera hispidula, Rhamnus californica and Umbellularia californica, although its pathogenicity has not been yet demonstrated on these species. Two brief articles now report findings of P. ramorum on two other species, both Gymnosperms.
P. ramorum was isolated in California from young trees showing leaf discoloration and cankers on branches, and on mature trees showing dying basal sprouts. P. ramorum was identified on the basis of morphology and molecular techniques. Inoculation studies were conducted on leaves and seedlings to test for pathogenicity. The authors note that, while P. ramorum causes a lethal canker on oak and tan oak, no unusual mortality or disease symptoms have been observed on overstory S. sempervirens, that the impact on understory S. sempervirens is unclear, but that P. ramorum seems to be able to kill sprouts.
P. ramorum was isolated in California from 3 young P. menziesii showing cankers on small branches, dieback of branches and leaf fall. P. ramorum was identified by morphological and molecular studies, and pathogenicity was tested. The authors note that no unusual mortality or disease symptoms have been observed on overstory P. menziesii, and the impact of tip branch dieback on the growth of the trees is unknown. Infection was found only at one location, at the vicinity of heavily infected Umbellularia californica trees. More studies are necessary to determine whether P. ramorum occurs on P. menziesii at other locations, or if it is limited to this single location.
Davidson, J.M.; Garbelotto, M.; Koike, S.T.; Rizzo, D.M. (2002) First report of Phytophthora ramorum on Douglas-Fir in California. Plant Disease 86(11), 1274.
Maloney, P.E.; Rizzo, D.M. (2002) First report of Phytophthora ramorum on Coast Redwood in California. Plant Disease 86(11), 1274.