01857nas a2200121 4500008004100000245009600041210006900137300001400206490000800220520144000228100002001668856004701688 2011 eng d00aA test system to quantify inoculum in runoff from Phytophthora ramorum-infected plant roots0 atest system to quantify inoculum in runoff from Phytophthora ram a1457-14640 v1013 a

Foliar hosts of Phytophthora ramorum are often susceptible to root infection but the epidemiological significance of such infections is unknown. A standardized test system was developed to quantify inoculum in runoff from root-infected Viburnum tinus ‘Spring Bouquet’ or Rhododendron ‘Cunningham’s White’ cuttings. Cuttings of both species gave off a maximum amount of inoculum 1 to 3 weeks after inoculation. The greatest amount of inoculum was recovered from Viburnum roots that were 48 to 70 days old at the time of inoculation, or roots incubated at 15 to 20°C rather than 25°C. Inoculum in runoff from inoculated Viburnum roots was similar for four different isolates of P. ramorum representing both the NA1 and EU1 lineages. When Rhododendron cuttings were inoculated with P. ramorum, P. citricola, or P. cactorum, inoculum of all three pathogens was recovered from runoff, with the highest amount recovered from plants inoculated with P. citricola, followed by the other two. Compared with the other two pathogens, P. ramorum colonized root tissue to a smaller extent. The epidemiology of root infection by P. ramorum is important in itself but the assay might lend itself for use in risk analysis for root infection of other plant species and evaluation of control measures, and also shed light on other root-infecting Phytophthora spp.

1 aShishkoff, Nina uhttp://dx.doi.org/10.1094/PHYTO-09-10-0260