Lineage, Temperature, and Host Species have Interacting Effects on Lesion Development in <i>Phytophthora ramorum</i>

Eyre, Catherine A.; Hayden, Katherine J.; Kozanitas, Melina; Grünwald, Niklaus J.; Garbelotto, Matteo

doi:10.1094/pdis-02-14-0151-re

Cited by 17 publications

(18 citation statements)

References 67 publications

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“…Although infection on bay laurel leaves can rebound quickly following drought conditions (Eyre et al. ), our results suggest that this may not necessarily increase pathogen spillover, because we also found that disease prevalence was greater when temperatures are consistently warm and wet. A generally warming climate would likely mean warmer temperatures year‐round, potentially increasing the success of pathogen spillover during the wet season, but also increasing heat exposure and reducing the pathogen load during the dry season.…”

Section: Discussionmentioning

confidence: 46%

Direct and indirect effects of forest microclimate on pathogen spillover

Dillon

Meentemeyer

2019

Ecology

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Disease dynamics are governed by variation of individuals, species, and environmental conditions across space and time. In some cases, an alternate reservoir host amplifies pathogen loads and drives disease transmission to less competent hosts in a process called pathogen spillover. Spillover is frequently associated with multi‐host disease systems where a single species is more tolerant of infection and more competent in pathogen transmission compared to other hosts. Pathogen spillover must be driven by biotic factors, including host and community characteristics, yet biotic factors interact with the abiotic environment (e.g., temperature) to create disease. Despite its fundamental role in disease dynamics, the influence of the abiotic environment on pathogen spillover has seldom been examined. Improving our understanding of disease processes such as pathogen spillover hinges on disentangling the effects of interrelated biotic and abiotic factors over space and time. We applied 10 yr of fine‐scale microclimate, disease, and tree community data in a path analysis to investigate the relative influence of biotic and abiotic factors on pathogen spillover for the emerging infectious forest disease sudden oak death (SOD). Disease transmission in SOD is primarily driven by the reservoir host California bay laurel, which supports high foliar pathogen loads that spillover onto neighboring oak trees and create lethal canker infections. The foliar pathogen load and susceptibility of oaks is expected to be sensitive to forest microclimate conditions. We found that biotic factors of pathogen load and tree diversity had relatively stronger effects on pathogen spillover compared to abiotic microclimate factors, with pathogen load increasing oak infection and tree diversity reducing oak infection. Abiotic factors still had significant effects, with greater heat exposure during summer months reducing pathogen loads and optimal pathogen conditions during the wet season increasing oak infection. Our results offer clues to possible disease dynamics under future climate change where hotter and drier or warmer and wetter conditions could have opposing effects on pathogen spillover in the SOD system. Disentangling direct and indirect effects of biotic and abiotic factors affecting disease processes can provide key insights into disease dynamics including potential avenues for reducing disease spread and predicting future epidemics.

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Section: Discussionmentioning

confidence: 46%

Direct and indirect effects of forest microclimate on pathogen spillover

Dillon

Meentemeyer

2019

Ecology

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“…On the contrary, in substrates with nil or negligible epidemiological role, either a high turnover of genotypes occurs (e.g., in water and soil), or genetic structural variations causing a significant change in phenotype can be observed (e.g., in oaks; Eyre et al. , ). Moreover, no genetic structure has been recorded when comparing populations from oaks and those from bays (Kasuga et al.…”

Section: Discussionmentioning

confidence: 99%

“…Zoospores were produced and counted as described in Eyre et al. (). Inoculations were performed as follows.…”

Section: Methodsmentioning

confidence: 99%

“…However, when spatial autocorrelation analyses were repeated in different years or seasons, thresholds of allelic overaggregation were 10 m in dry years, but increased to at least 200 m in wet years (Eyre et al. ). It should be noted that these studies are based on isolations of the pathogen from bay laurel leaves, and it has been shown that even low numbers of propagules can cause foliar infections (Hüberli et al.…”

Section: Introductionmentioning

confidence: 99%

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The ecology of infection between a transmissive and a dead‐end host provides clues for the treatment of a plant disease

et al. 2017

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Abstract. In plant pathosystems in which some hosts are transmissive and some are dead-ends, infection is mediated by multiple factors including the susceptibility of both hosts, the sporulation potential of transmissive hosts, the mobility of infectious propagules, the presence of environmental factors conducive to infection, and the variability in distribution of both host types. The factors above were studied for the California forest disease sudden oak death caused by the pathogen Phytophthora ramorum. This pathogen is exotic to California, and while it sporulates at significant levels on the leaves of California bay laurels, four susceptible oak species appear to be non-infectious dead-end hosts. Here, we report, for the first time, on inoculum levels necessary to successfully infect adult oaks and on the distribution of such inoculum levels through time and space thanks to a seven-year-long monitoring effort across a network of 128 monitoring points. Through a series of geostatistical and statistical analyses, we show that the presence of high inoculum loads is positively correlated with close proximity to bay laurels, with high rainfall levels, and with warmer temperatures. Data are consistent with splash dispersal of the pathogen and show that increased presence of tanoak corresponds to a reduced presence of bay laurels and to a lower frequency of high inoculum events. Removal of bay laurels resulted in a substantial decrease of number of events in which spore loads were high enough to infect oaks. This effect was significant when bays were removed 10 m around sampling points, thus indicating that removal of bays 10 m around oaks is a valid approach to reduce infections of oaks.

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“…In all trials, the severity of symptoms was significantly different between treatments and controls, further indicating that the length of the experiments was sufficient to draw conclusions, and saved us the unnecessary use of resources associated with longer trials. Additionally, it should be pointed out that other researchers have routinely performed experiments of comparable length to assess the virulence of Phytophthora species (Eyre, Hayden, Kozanitas, Grünwald, & Garbelotto, ) including P. cactorum (Lilja, Karjalainen, Parikka, Kammiovirta, & Nuorteva, ) and P. tentaculata (Meng & Wang, ; Rooney‐Latham & Blomquist, ). Although mortality (a qualitative variable) can be assessed using longer experiments, quantitative variables including canker size and severity of canopy symptoms are often biased in longer trials, because the size of lesions and the appearance of the canopy cannot be considered reliable when plants are dead.…”

Section: Discussionmentioning

confidence: 99%

Susceptibility to the rare Phytophthora tentaculata and to the widespread Phytophthora cactorum is consistent with host ecology and history

Sims

Garbelotto

2018

Forest Pathology

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We evaluated the susceptibility of three California endemic plant species Heteromeles arbutifolia, Platanus racemosa and Quercus agrifolia to the two congeneric soilborne pathogen species: Phytophthora tentaculata and Phytophthora cactorum. These pathogens were recently introduced in ecosystems east of the San Francisco Bay, where the three plant species above are dominant. Phytophthora cactorum has a worldwide distribution inclusive of California, and a broad host range. Phytophthora tentaculata, in contrast, is suspected to be a “new” exotic to California and has been described on relatively few hosts. By separately challenging the roots and the stems of the three plant species above, we show that: (a) Both were equally pathogenic, but the type of disease differed based on host; (b) disease was consistent with host ecology and with previous disease reports, even if caused by different Phytophthora spp. and; (c) there were intraspecific differences in virulence. This study provides the following significant information regarding the management and early modelling of polyphagous soilborne Phytophthoras: (a) Endemic species can be as problematic as recently introduced exotics. (b) Multiple introductions should be avoided due to varying virulence levels among genotypes. (c) Riparian species like P. racemosa may develop disease tolerance in their root systems, but remain susceptible in their aerial portions, and thus, diseases could be facilitated by flooding or splash of infectious structures of soilborne pathogens onto aerial plant portions.

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

Cited by 17 publications

References 67 publications

Direct and indirect effects of forest microclimate on pathogen spillover

Direct and indirect effects of forest microclimate on pathogen spillover

The ecology of infection between a transmissive and a dead‐end host provides clues for the treatment of a plant disease

Susceptibility to the rare Phytophthora tentaculata and to the widespread Phytophthora cactorum is consistent with host ecology and history

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