Phytophthora ramorum Does Not Cause Physiologically Significant Systemic Injury to California Bay Laurel, Its Primary Reservoir Host

California bay laurel trees (Umbellularia californica) play a crucial role in the reproduction and survival of Phytophthora ramorum in coastal California forests by supporting sporulation during the rainy season and by providing a means for the pathogen to survive the dry, Mediterranean summer. While bay laurel is thus critical to the epidemiology of sudden oak death and other P. ramorum diseases in California, the relatively minor symptoms observed on this reservoir host suggest that it may not sustain ecologically significant injury itself. The long-term role that P. ramorum will play in California forests will depend in part on the extent to which this pathogen decreases the ecological fitness of bay laurel. Despite the importance of this question, no study has yet investigated in detail the physiological impact that ramorum blight imposes on bay laurel. This experimental study quantifies the impact that P. ramorum has on artificially inoculated bay laurel seedlings with measurements that integrate the full injury that infection with an oomycete may cause: photosynthetic efficiency, total photosynthetic area, and growth. Leaf area and leaf mass were not impacted significantly by infection of P. ramorum. Photosynthetic efficiency was mildly depressed in symptomatic, but not asymptomatic leaves, despite unnaturally high levels of necrosis that were imposed on the seedlings. These results demonstrate that bay laurel trees suffer only minor injury from ramorum blight beyond visible necrotic symptoms. Consequently, it is highly likely that bay laurel will continue to be widely available as a host for P. ramorum in California forests, which has long-term implications for the composition of these forests.

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Microclimate Impacts Survival and Prevalence of Phytophthora ramorum in Umbellularia californica, a Key Reservoir Host of Sudden Oak Death in Northern California Forests

PLoS ONE ◽

10.1371/journal.pone.0098195 ◽

2014 ◽

Vol 9 (8) ◽

pp. e98195 ◽

Cited By ~ 8

Author(s):

Matthew V. DiLeo ◽

Richard M. Bostock ◽

David M. Rizzo

Keyword(s):

Reservoir Host ◽

Phytophthora Ramorum ◽

Sudden Oak Death ◽

Northern California ◽

Umbellularia Californica

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Variation in Susceptibility of Tanoak to the NA1 and EU1 Lineages of Phytophthora ramorum, the Cause of Sudden Oak Death

Plant Disease ◽

10.1094/pdis-04-19-0831-re ◽

2019 ◽

Vol 103 (12) ◽

pp. 3154-3160 ◽

Cited By ~ 1

Author(s):

Kelsey L. Søndreli ◽

Alan Kanaskie ◽

Susanna Keriö ◽

Jared M. LeBoldus

Keyword(s):

Disease Resistance ◽

Forest Ecosystems ◽

Phytophthora Ramorum ◽

Sudden Oak Death ◽

Artificial Inoculation ◽

Lesion Length ◽

Significant Difference ◽

Notholithocarpus Densiflorus ◽

The Impact ◽

Inoculation Assay

Phytophthora ramorum, the cause of sudden oak death (SOD), kills tanoak (Notholithocarpus densiflorus) trees in southwestern Oregon and California. Two lineages of P. ramorum are now found in wildland forests of Oregon (NA1 and EU1). In addition to the management of SOD in forest ecosystems, disease resistance could be used as a way to mitigate the impact of P. ramorum. The objectives of this study were to (i) characterize the variability in resistance of N. densiflorus among families using lesion length; (ii) determine whether lineage, isolate, family, or their interactions significantly affect variation in lesion length; and (iii) determine whether there are differences among isolates and among families in terms of lesion length. The parameters isolate nested within lineage (isolate[lineage]) and family × isolate(lineage) interaction explained the majority of the variation in lesion length. There was no significant difference between the NA1 and EU1 lineages in terms of mean lesion length; however, there were differences among the six isolates. Lesions on seedlings collected from surviving trees at infested sites were smaller, on average, than lesions of seedlings collected from trees at noninfested sites (P = 0.0064). The results indicate that there is potential to establish a breeding program for tanoak resistance to SOD and that several isolates of P. ramorum should be used in an artificial inoculation assay.

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Efficacy of Heat-based Treatments in Eliminating the Recovery of the Sudden Oak Death Pathogen (Phytophthora ramorum) from Infected California Bay Laurel Leaves

HortScience ◽

10.21273/hortsci.39.7.1677 ◽

2004 ◽

Vol 39 (7) ◽

pp. 1677-1680 ◽

Cited By ~ 11

Author(s):

Tamar Y. Harnik ◽

Monica Mejia-Chang ◽

James Lewis ◽

Matteo Garbelotto

Keyword(s):

Plant Pathogen ◽

Negative Impact ◽

Phytophthora Ramorum ◽

Sudden Oak Death ◽

Heating Process ◽

Foliar Disease ◽

Umbellularia Californica ◽

Heat Tolerant ◽

Prolonged Heat

Phytophthora ramorum (Oomycota) (Werres et al., 2001) is the plant pathogen responsible for the lethal disease of several oak species in California known as sudden oak death. The pathogen also causes a foliar disease on Umbellularia californica (bay laurel or simply bay). Bay leaves have been identified as the major source of natural inoculum in California coastal woodlands. Because of the epidemiological relevance of bay leaves, their movement needs to be regulated. Our study shows that P. ramorum is highly heat tolerant and can be reisolated from artificially inoculated bay laurel leaves placed at 55 °C for up to 1 week. The pathogen cannot be recovered after 2 weeks at 55 °C. Prolonged heat treatments, however, are impractical for bay leaves intended to be sold commercially as a spice, since they negatively impact the quality of the leaves. Here we describe a treatment involving a progressive and gradual heating process combined with the application of moderate vacuum. This method can be completed in 22 hours and is shown here to eliminate the recovery of P. ramorum without having a negative impact on the quality of the bay leaves.

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Detection, Distribution, Sporulation, and Survival of Phytophthora ramorum in a California Redwood-Tanoak Forest Soil

Phytopathology ◽

10.1094/phyto-97-10-1366 ◽

2007 ◽

Vol 97 (10) ◽

pp. 1366-1375 ◽

Cited By ~ 46

Author(s):

E. J. Fichtner ◽

S. C. Lynch ◽

D. M. Rizzo

Keyword(s):

Phytophthora Ramorum ◽

Disease Cycle ◽

Soil Baiting ◽

Umbellularia Californica ◽

Lithocarpus Densiflorus ◽

Important Host ◽

The Impact ◽

Soil Interface ◽

Leaf Disks

Recovery of Phytophthora ramorum from soils throughout sudden oak death-affected regions of California illustrates that soil may serve as an inoculum reservoir, but the role of soil inoculum in the disease cycle is unknown. This study addresses the efficacy of soil baiting, seasonal pathogen distribution under several epidemiologically important host species, summer survival and chlamydospore production in soil, and the impact of soil drying on pathogen survival. The efficacy of rhododendron leaves and pears as baits for detection of soilborne propagules were compared. Natural inoculum associated with bay laurel (Umbellularia californica), tanoak (Lithocarpus densiflorus), and redwood (Sequoia sempervirens) were determined by monthly baiting. Summer survival and chlamydospore production were assessed in infected rhododendron leaf disks incubated under bay laurel, tanoak, and redwood at either the surface, the litter/soil interface, or in soil. Rhododendron leaf baits were superior to pear baits for sporangia detection, but neither bait detected chlamydospores. Most inoculum was associated with bay laurel and recovery was higher in soil than litter. Soil-incubated inoculum exhibited over 60% survival at the end of summer and also supported elevated chlamydospore production. P. ramorum survives and produces chlamydospores in forest soils over summer, providing a possible inoculum reservoir at the onset of the fall disease cycle.

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Host Phenology and Leaf Effects on Susceptibility of California Bay Laurel to Phytophthora ramorum

Phytopathology ◽

10.1094/phyto-01-15-0016-r ◽

2016 ◽

Vol 106 (1) ◽

pp. 47-55 ◽

Cited By ~ 4

Author(s):

Steven F. Johnston ◽

Michael F. Cohen ◽

Tamas Torok ◽

Ross K. Meentemeyer ◽

Nathan E. Rank

Keyword(s):

Leaf Age ◽

Spore Production ◽

Phytophthora Ramorum ◽

Sudden Oak Death ◽

Forest Disease ◽

Umbellularia Californica ◽

Leaf Surfaces ◽

Multiple Trees ◽

The Relationship ◽

Plant Susceptibility

Spread of the plant pathogen Phytophthora ramorum, causal agent of the forest disease sudden oak death, is driven by a few competent hosts that support spore production from foliar lesions. The relationship between traits of a principal foliar host, California bay laurel (Umbellularia californica), and susceptibility to P. ramorum infection were investigated with multiple P. ramorum isolates and leaves collected from multiple trees in leaf-droplet assays. We examined whether susceptibility varies with season, leaf age, or inoculum position. Bay laurel susceptibility was highest during spring and summer and lowest in winter. Older leaves (>1 year) were more susceptible than younger ones (8 to 11 months). Susceptibility was greater at leaf tips and edges than the middle of the leaf. Leaf surfaces wiped with 70% ethanol were more susceptible to P. ramorum infection than untreated leaf surfaces. Our results indicate that seasonal changes in susceptibility of U. californica significantly influence P. ramorum infection levels. Thus, in addition to environmental variables such as temperature and moisture, variability in host plant susceptibility contributes to disease establishment of P. ramorum.

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Suppressed, but Not Forgotten

Swiss Journal of Psychology ◽

10.1024/1421-0185/a000033 ◽

2011 ◽

Vol 70 (1) ◽

pp. 5-11 ◽

Cited By ~ 8

Author(s):

Beat Meier ◽

Anja König ◽

Samuel Parak ◽

Katharina Henke

Keyword(s):

Memory Trace ◽

Thought Suppression ◽

Test Phase ◽

Indirect Test ◽

Final Test ◽

Test Experiment ◽

And Control ◽

Cue Words ◽

The Impact

This study investigates the impact of thought suppression over a 1-week interval. In two experiments with 80 university students each, we used the think/no-think paradigm in which participants initially learn a list of word pairs (cue-target associations). Then they were presented with some of the cue words again and should either respond with the target word or avoid thinking about it. In the final test phase, their memory for the initially learned cue-target pairs was tested. In Experiment 1, type of memory test was manipulated (i.e., direct vs. indirect). In Experiment 2, type of no-think instructions was manipulated (i.e., suppress vs. substitute). Overall, our results showed poorer memory for no-think and control items compared to think items across all experiments and conditions. Critically, however, more no-think than control items were remembered after the 1-week interval in the direct, but not in the indirect test (Experiment 1) and with thought suppression, but not thought substitution instructions (Experiment 2). We suggest that during thought suppression a brief reactivation of the learned association may lead to reconsolidation of the memory trace and hence to better retrieval of suppressed than control items in the long term.

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