01997nas a2200157 4500008004100000245010700041210006900148260001200217300001400229490000800243520145800251100002001709700002101729700002301750856006601773 2013 eng d00aInoculum density relationships for infection of some eastern US forest species by Phytophthora ramorum0 aInoculum density relationships for infection of some eastern US  c09/2013 a595–6030 v1613 a
Our objectives were to establish inoculum density relationships between P. ramorum and selected hosts using detached leaf and whole-plant inoculations. Young plants and detached leaves of Quercus prinus (Chestnut oak), Q. rubra (Northern red oak), Acer rubrum (red maple), Kalmia latifolia (mountain laurel) and Rhododendron ‘Cunningham's White’ were dip-inoculated with varying numbers of P. ramorum sporangia, and the total number of diseased and healthy leaves recorded following incubation at 20°C and 100% relative humidity. Calibration threshold estimates for obtaining 50% infected leaves based on linear analysis ranged from 36 to 750 sporangia/ml for the five hosts. Half-life (LD50) estimates (the number of spores for which the per cent of diseased leaves reaches 50% of its total) from asymptotic regression analysis ranged from 94 to 319 sporangia/ml. Statistically significant differences (P = 0.0076) were observed among hosts in per cent infection in response to increased inoculum density. Inoculum threshold estimates based on studies with detached leaves were comparable to those obtained using whole plants. The results provide estimates of inoculum levels necessary to cause disease on these five P. ramorum hosts and will be useful in disease prediction and for development of pest risk assessments.
1 aTooley, Paul, W1 aBrowning, Marsha1 aLeighty, Robert, M uhttp://onlinelibrary.wiley.com/doi/10.1111/jph.12107/abstract01536nas a2200169 4500008004100000022001400041245009300055210006900148260002900217300001200246520097500258653001801233653001901251100002001270700002101290856005501311 2011 eng d a1439-043400aEnhanced recovery of Phytophthora ramorum from soil following 30 Days of storage at 4°C0 aEnhanced recovery of Phytophthora ramorum from soil following 30 bBlackwell Publishing Ltd ano–no3 a

Chlamydospores of Phytophthora ramorum were used to infest field soil at densities ranging from 0.2 to 42 chlamydospores/cm3 soil. Recovery was determined by baiting with rhododendron leaf discs and dilution plating at time 0 and after 30 days of storage at 4°C, as recommended by USDA-APHIS. Baiting was slightly more sensitive than dilution plating in recovering P. ramorum immediately following infestation of soil and allowed detection from samples infested with as little as 0.2 chlamydospores/cm3 compared with 1 chlamydospore/cm3 for dilution plating. After 30 days of infested soil storage at 4°C, P. ramorum was detected at significantly (P = 0.05) higher levels than at time 0 with both recovery methods. The results indicate that storage of P. ramorum-infested soil at 4°C may allow for pathogen activity, such as sporangia production, which may enhance recovery from soil.

10achlamydospore10aramorum blight1 aTooley, Paul, W1 aCarras, Marie, M uhttp://dx.doi.org/10.1111/j.1439-0434.2011.01810.x02402nas a2200145 4500008004100000245011000041210006900151260001300220300001400233490000800247520192100255100002002176700002102196856003902217 2016 eng d00aThe Effect of Exposure to Decreasing Relative Humidity on the Viability of Phytophthora ramorum sporangia0 aEffect of Exposure to Decreasing Relative Humidity on the Viabil cAug 2016 a874 - 8810 v1643 a

Sporangia of three isolates of Phytophthora ramorum representing three different clonal lineages were subjected to relative humidity (RH) levels between 80 and 100% for exposure periods ranging from 1 to 24 h at 20°C in darkness. Plastic containers (21.5 × 14.5 × 5 cm) were used as humidity chambers with 130 ml of glycerine solution added to each container. Glycerine concentrations corresponded to 100, 95, 90, 85 and 80% RH based on refractive index measurements. Sporangia suspensions were pipeted onto nitrile mesh squares (1.5 × 1.5 cm, 15 micron pore size) which were placed in the humidity chambers and incubated at 20°C in darkness. Following exposure periods of 1, 2, 4, 8, 12 and 24 h, mesh squares were inverted onto Petri dishes of selective medium and sporangia germination assessed after 24 and 48 h. At 100% RH, we observed a mean value of 88% germination after 1 h exposure declining to 18% germination following 24 h incubation. At 95% RH, a steeper decline in germination was noted, with means ranging from 79% at 1 h to less than 1% at 24 h exposure. At 90% RH, no germination was noted after 8 or more h exposure, and values were 57%, 22% and 3% germination for the 1, 2 and 4 h exposures, respectively. Germination was only observed at 1 h exposure for both the 85% RH treatment (52% germination) and the 80% RH treatment (38% germination). The three isolates responded similarly over the range of RH values tested. The germination response of P. ramorum sporangia to RH values between 80% and 100% was comparable to that reported for other Phytophthora species. Knowledge of conditions that affect Pramorum sporangia germination can shed light on pathogenesis and epidemic potential and lead to improved control recommendations.

1 aTooley, Paul, W1 aBrowning, Marsha uhttps://doi.org/10.1111/jph.12506 01645nas a2200157 4500008004100000245012200041210006900163260001600232300001400248490000800262520111000270100002001380700002101400700002301421856004301444 2014 eng d00aEffects of Inoculum Density and Wounding on Stem Infection of Three Eastern US Forest Species by Phytophthora ramorum0 aEffects of Inoculum Density and Wounding on Stem Infection of Th cJan-03-2014 a683 - 6890 v1623 a

Seedlings of three Eastern US forest species Quercus rubra (northern red oak), Quercus prinus (chestnut oak) and Acer rubrum (red maple) were inoculated by applying Phytophthora ramorum sporangia to stems at different inoculum densities with and without wounding. Disease occurred in all treatments involving wounds, and no disease was observed in unwounded treatments. Younger seedlings (2–3 years old) did not differ significantly from older seedlings (5–6 years old) in disease incidence, but older seedlings sustained smaller lesions compared with younger seedlings. For both old and young seedlings, disease on wounded stems was observed down to the lowest sporangia concentration utilized (500 sporangia/ml for old seedlings and 100 sporangia/ml for young seedlings). The results show that in the presence of wounding, even very low sporangia concentrations can result in disease, and further suggest that wounding caused by insects and other factors may play an important role in P. ramorum epidemiology in forest environments.

1 aTooley, Paul, W1 aBrowning, Marsha1 aLeighty, Robert, M uhttp://doi.wiley.com/10.1111/jph.12251