Susceptibility in Viburnum to Phytophthora ramorum

Abstract

Phytophthora ramorum, the causal agent of sudden oak death on oak and tanoak and Ramorum blight or Ramorum shoot dieback on ornamentals, is a recently emerged pathogen. Viburnum is a genus of commonly grown ornamental shrubs known to be susceptible to P. ramorum. The entire genus has been placed on the P. ramorum host list. The range of susceptibility of genotypes in the genus is currently not understood. We evaluated whether or not cultivars in the genus Viburnum differ in susceptibility to P. ramorum in controlled, detached leaf inoculations using two isolates belonging to the two clonal lineages found in Oregon. The genus Viburnum shows remarkable differences in susceptibility to infection by P. ramorum. Viburnum genotypes differed significantly in susceptibility to P. ramorum in detached leaf inoculations. V. × burkwoodii was consistently the most susceptible host genotype, followed by V. plicatum ‘Mariesii’ and V. lentago. Most cultivars evaluated for resistance to P. ramorum were not susceptible or developed only small lesions as determined with a detached leaf assay. Our work only provides information on leaf based resistance, and inferences on epidemic development in whole canopies and under field conditions cannot currently be made.

Lineage, Temperature, and Host Species have Interacting Effects on Lesion Development in Phytophthora ramorum

“…There have been a number of published trials aimed at testing pathogen aggressiveness and host susceptibility and at comparing a variety of other phenotypic traits between clonal lineages and iso lates (1,7,15,20,35,36,40,41,51,54,58,64,65). However, these indi vidual trials have not included a representative population of isolates or a range of hosts and temperatures simultaneously.…”

Will all the trees fall? Variable resistance to an introduced forest disease in a highly susceptible host

“…Under-bark inoculations of branches detached from Quercus species have been used to assess variation in resistance to ramorum blight (Dodd et al, 2005;Dodd et al, 2008b;Hüberli et al, 2006a), but in tanoaks this method frequently yields nearly invisible lesions and large measurement error, precluding its use on a large scale (Hayden and Garbelotto, unpublished data). Detached-leaf inoculations with zoospore suspensions, both wounding and nonwounding, have been used to gauge host resistance to P. ramorum in its foliar hosts (Anacker et al, 2008;De Dobbelaere et al, 2010;Grünwald et al, 2008;Hüberli et al, 2006a). But tanoak leaves, again, often develop asymptomatic infections from zoospore solutions (Hansen et al, 2005).…”

Genotypic and phenotypic characterization of the European A2 isolates of Phytophthora ramorum

“…Previous studies showed similar phenotypic differences between European and North American isolates (Brasier 2003;Brasier et al 2006;DEFRA Science and Research 2004;Grünwald et al 2008a;Hüberli et al 2006;Tooley et al 2004;Werres and Kaminski 2005). However, other studies did not report any differences on a variety of other host species Grünwald et al 2008b;Hüberli et al 2006;Tooley et al 2004;Werres and Kaminski 2005). Variation in aggressiveness among isolates within both NA1 and EU1 lineages has been documented on coast live oak seedlings, detached bay laurel leaves and Q. rubra cut stems (Brasier et al 2006;Hüberli et al 2006).…”