Virulence of five Phytophthora species causing rhododendron root rot in Oregon.

Plant Disease ◽  
2021 ◽  
Author(s):  
Gabe O. Sacher ◽  
Carolyn F. Scagel ◽  
E. Anne Davis ◽  
Bryan R. Beck ◽  
Jerry E. Weiland
Keyword(s):  
Root Rot ◽  
Phytophthora Cinnamomi ◽  
Block Design ◽  
Abundant Species ◽  
Phytophthora Species ◽  
Phytophthora Root Rot ◽  
Moderate Disease ◽  
Randomized Complete Block Design ◽  
Infested Field ◽  
Production Areas

Phytophthora root rot is a destructive disease of rhododendron, causing substantial losses of this nursery crop in infested field and container production areas. Historically, Phytophthora cinnamomi was considered the main causal agent of the disease. However, a recent survey of soilborne Phytophthora species from symptomatic rhododendrons in Oregon revealed that P. plurivora is more common than P. cinnamomi and that several other Phytophthora species may also be involved. We investigated the ability of the five most abundant species from the survey to cause root rot: P. plurivora, P. cinnamomi, P. pini, P. pseudocryptogea, and P. cambivora. Three to four isolates were selected for each species from across six Oregon nurseries. Media of containerized Rhododendron catawbiense ‘Boursault’ was infested with single isolates in a randomized complete block design in a greenhouse. Phytophthora cinnamomi, P. pini, and P. plurivora rapidly caused ≥ 90% incidence of severe root rot while P. pseudocryptogea caused more moderate disease with 46% incidence of severe root rot. Phytophthora cambivora failed to produce enough inoculum and was used at a lower inoculum density than the other four species, but occasionally caused severe root rot (5% incidence). No differences in virulence were observed among isolates of same species, except for one isolate of P. plurivora that caused less disease than other P. plurivora isolates. This study demonstrates that all five Phytophthora species, which were representative of 94% of the survey isolates, are capable of causing severe root rot and plant death, but that not all species are equally virulent.

scholarly journals Variation in Disease Severity Caused by Phytophthora cinnamomi, P. plurivora, and Pythium cryptoirregulare on Two Rhododendron Cultivars

Plant Disease ◽  
2018 ◽  
Vol 102 (12) ◽  
pp. 2560-2570 ◽  
Author(s):  
Jerry E. Weiland ◽  
Carolyn F. Scagel ◽  
Niklaus J. Grünwald ◽  
E. Anne Davis ◽  
Bryan R. Beck ◽  
...  
Keyword(s):  
Disease Control ◽  
Root Rot ◽  
Phytophthora Cinnamomi ◽  
Severe Disease ◽  
Phytophthora Species ◽  
Relative Resistance ◽  
Inoculum Level ◽  
Phytophthora Root Rot ◽  
Mild Disease ◽  
Comparative Information

Rhododendrons are an important crop in the ornamental nursery industry, but are prone to Phytophthora root rot. Phytophthora root rot is a continuing issue on rhododendrons despite decades of research. Several Phytophthora species are known to cause root rot, but most research has focused on P. cinnamomi, and comparative information on pathogenicity is limited for other commonly encountered oomycetes, including Phytophthora plurivora and Pythium cryptoirregulare. In this study, three isolates each of P. cinnamomi, P. plurivora, and Py. cryptoirregulare were used to inoculate rhododendron cultivars Cunningham’s White and Yaku Princess at two different inoculum levels. All three species caused disease, especially at the higher inoculum level. P. cinnamomi and P. plurivora were the most aggressive pathogens, causing severe root rot, whereas Py. cryptoirregulare was a weak pathogen that only caused mild disease. Within each pathogen species, isolate had no influence on disease. Both P. cinnamomi and P. plurivora caused more severe disease on Cunningham’s White than on Yaku Princess, suggesting that the relative resistance and susceptibility among rhododendron cultivars might be similar for both pathogens. Reisolation of P. cinnamomi and P. plurivora was also greater from plants exhibiting aboveground symptoms of wilting and plant death and belowground symptoms of root rot than from those without symptoms. Results show that both P. cinnamomi and P. plurivora, but not Py. cryptoirregulare, are important pathogens causing severe root rot in rhododendron. This study establishes the risks for disease resulting from low and high levels of inoculum for each pathogen. Further research is needed to evaluate longer term risks associated with low inoculum levels on rhododendron health and to explore whether differences among pathogen species affect disease control.

scholarly journals Interactions Between Root Rotting Phytophthora, Abies Christmas Trees, and Environment

Plant Disease ◽  
2019 ◽  
Vol 103 (3) ◽  
pp. 538-545 ◽  
Author(s):  
Kathleen M. McKeever ◽  
Gary A Chastagner
Keyword(s):  
Host Species ◽  
Root Rot ◽  
Regional Scale ◽  
Phytophthora Species ◽  
Host Responses ◽  
Phytophthora Root Rot ◽  
Ambient Temperatures ◽  
Christmas Trees ◽  
Host Mortality ◽  
Production Areas

Defining host-pathogen interactions between species of root-rotting Phytophthora and Abies in Christmas tree production areas is important for tailoring management activities on a regional scale and for developing molecular tools for identifying resistant host species. Classifying Abies species as resistant or susceptible is complicated by regional variation in abundance and aggressiveness of Phytophthora species and the influence of environment on symptom expression and host vigor. Because previous studies performed to assess host response to Phytophthora root rot (PRR) have focused on one or a few species of either the host or pathogen, a multifactorial experiment was conducted to assess the responses of seven species of Abies challenged with three isolates each of four Phytophthora species under contrasting temperature conditions. Evaluation of mortality, root rot severity, and remaining root biomass after 16 weeks of exposure to the pathogen confirmed prior inferences regarding inherent variation in the resistance responses of various species of Abies and demonstrated evidence of variation in aggressiveness among species of Phytophthora as well as different isolates of the same Phytophthora species. The ambient temperatures at which studies were conducted had a conspicuous effect on host mortality, root rot severity, and radial growth of Phytophthora. Understanding how host responses differ under variable pathogen attack and ambient environment will improve efforts to control PRR using host species substitutions on infested ground.

scholarly journals Cellulase Activity as a Mechanism for Suppression of Phytophthora Root Rot in Mulches

2011 ◽  
Vol 101 (2) ◽  
pp. 223-230 ◽  
Author(s):  
Brantlee Spakes Richter ◽  
Kelly Ivors ◽  
Wei Shi ◽  
D. M. Benson
Keyword(s):  
Root Rot ◽  
Phytophthora Cinnamomi ◽  
Cellulase Activity ◽  
Enzyme Concentration ◽  
Disease Suppression ◽  
In Vitro Assays ◽  
Infested Soil ◽  
Phytophthora Root Rot ◽  
Standard Curve

Wood-based mulches are used in avocado production and are being tested on Fraser fir for reduction of Phytophthora root rot, caused by Phytophthora cinnamomi. Research with avocado has suggested a role of microbial cellulase enzymes in pathogen suppression through effects on the cellulosic cell walls of Phytophthora. This work was conducted to determine whether cellulase activity could account for disease suppression in mulch systems. A standard curve was developed to correlate cellulase activity in mulches with concentrations of a cellulase product. Based on this curve, cellulase activity in mulch samples was equivalent to a cellulase enzyme concentration of 25 U ml–1 or greater of product. Sustained exposure of P. cinnamomi to cellulase at 10 to 50 U ml–1 significantly reduced sporangia production, but biomass was only reduced with concentrations over 100 U ml–1. In a lupine bioassay, cellulase was applied to infested soil at 100 or 1,000 U ml–1 with three timings. Cellulase activity diminished by 47% between 1 and 15 days after application. Cellulase applied at 100 U ml–1 2 weeks before planting yielded activity of 20.08 μmol glucose equivalents per gram of soil water (GE g–1 aq) at planting, a level equivalent to mulch samples. Cellulase activity at planting ranged from 3.35 to 48.67 μmol GE g–1 aq, but no treatment significantly affected disease progress. Based on in vitro assays, cellulase activity in mulch was sufficient to impair sporangia production of P. cinnamomi, but not always sufficient to impact vegetative biomass.

scholarly journals Phytophthora mediterranea sp. nov., a New Species Closely Related to Phytophthora cinnamomi from Nursery Plants of Myrtus communis in Italy

Forests ◽  
2021 ◽  
Vol 12 (6) ◽  
pp. 682
Author(s):  
Carlo Bregant ◽  
Antonio A. Mulas ◽  
Giovanni Rossetto ◽  
Antonio Deidda ◽  
Lucia Maddau ◽  
...  
Keyword(s):  
New Species ◽  
Root Rot ◽  
Phytophthora Cinnamomi ◽  
Colony Growth ◽  
Phytophthora Species ◽  
Maximum Temperature ◽  
Pathogenicity Test ◽  
Forest Nurseries ◽  
Collar And Root Rot ◽  
A New Species

Monitoring surveys of Phytophthora related diseases in four forest nurseries in Italy revealed the occurrence of fourteen Phytophthora species to be associated with collar and root rot on fourteen plants typical of Mediterranean and alpine regions. In addition, a multilocus phylogeny analysis based on nuclear ITS and ß-tubulin and mitochondrial cox1 sequences, as well as micromorphological features, supported the description of a new species belonging to the phylogenetic clade 7c, Phytophthora mediterranea sp. nov. Phytophthora mediterranea was shown to be associated with collar and root rot symptoms on myrtle seedlings. Phylogenetically, P. mediterranea is closely related to P. cinnamomi but the two species differ in 87 nucleotides in the three studied DNA regions. Morphologically P. mediterranea can be easily distinguished from P. cinnamomi on the basis of its smaller sporangia, colony growth pattern and higher optimum and maximum temperature values. Data from the pathogenicity test showed that P. mediterranea has the potential to threaten the native Mediterranean maquis vegetation. Finally, the discovery of P. cinnamomi in alpine nurseries, confirms the progressive expansion of this species towards cold environments, probably driven by climate change.

scholarly journals Soilborne Phytophthora and Pythium Diversity From Rhododendron in Propagation, Container, and Field Production Systems of the Pacific Northwest

Plant Disease ◽  
2020 ◽  
Vol 104 (6) ◽  
pp. 1841-1850
Author(s):  
Jerry E. Weiland ◽  
Carolyn. F. Scagel ◽  
Niklaus J. Grünwald ◽  
E. Anne Davis ◽  
Bryan R. Beck ◽  
...  
Keyword(s):  
Disease Control ◽  
Pacific Northwest ◽  
Root Rot ◽  
Production Systems ◽  
Phytophthora Cinnamomi ◽  
Phytophthora Species ◽  
Pythium Species ◽  
Disease Etiology ◽  
The Past ◽  
Field Systems

Rhododendron root rot is a severe disease that causes significant mortality in rhododendrons. Information is needed about the incidence and identity of soilborne Phytophthora and Pythium species causing root rot in Pacific Northwest nurseries in order to better understand the disease etiology and to optimize disease control strategies. The last survey focusing solely on soilborne oomycete pathogens in rhododendron production was conducted in 1974. Since then, advances in pathogen identification have occurred, new species may have been introduced, pathogen communities may have shifted, and little is known about Pythium species affecting this crop. Therefore, a survey of root-infecting Phytophthora and Pythium species was conducted at seven nurseries from 2013 to 2017 to (i) document the incidence of root rot damage at each nursery and stage of production, (ii) identify soilborne oomycetes infecting rhododendron, and (iii) determine whether there are differences in pathogen diversity among nurseries and production systems. Rhododendrons from propagation, container, and field systems were sampled and Phytophthora and Pythium species were isolated from the roots and collar region. Root rot was rarely evident in propagation systems, which were dominated by Pythium species. However, severe root rot was much more common in container and field systems where the genus Phytophthora was also more prevalent, suggesting that Phytophthora species are the primary cause of severe root rot and that most contamination by these pathogens comes in after the propagation stage. In total, 20 Pythium species and 11 Phytophthora species were identified. Pythium cryptoirregulare, Pythium aff. macrosporum, Phytophthora plurivora, and Phytophthora cinnamomi were the most frequently isolated species and the results showed that Phytophthora plurivora has become much more common than in the past. Phytophthora diversity was also greater in field systems than in propagation or container systems. Risks for Phytophthora contamination were commonly observed during the survey and included placement of potting media in direct contact with field soil, the presence of dead plants that could serve as continuous sources of inoculum, and the presence of excess water as a result of poor drainage, overirrigation, or malfunctioning irrigation equipment. In the past, research on disease development and root rot disease control in rhododendron focused almost exclusively on Phytophthora cinnamomi. More research is needed on both of these topics for the other root-infecting species identified in this survey.

scholarly journals Temporal and Spatial Epidemiology of Phytophthora Root Rot in Fraser Fir Plantations

Plant Disease ◽  
2006 ◽  
Vol 90 (9) ◽  
pp. 1171-1180 ◽  
Author(s):  
D. M. Benson ◽  
L. F. Grand ◽  
C. S. Vernia ◽  
T. R. Gottwald
Keyword(s):  
Spatial Analysis ◽  
Root Rot ◽  
Phytophthora Cinnamomi ◽  
Local Area ◽  
Slope Aspect ◽  
Mortality Data ◽  
Phytophthora Root Rot ◽  
Fraser Fir ◽  
Incidence And Mortality ◽  
Over Time

In 1999, 19 plots of Fraser fir (Abies fraseri) with a disease focus were established in commercial plantings grown for Christmas tree production in the mountains of five western North Caro-lina counties. Progress of Phytophthora root rot caused by Phytophthora cinnamomi as estimated by mortality was followed in each plot over 3 to 4 years in an attempt to understand dispersal of inoculum. Slope, aspect, and field production age at the time plots were established were recorded. Rainfall estimated from National Weather Service stations each growing season also was recorded. The relationship of site parameters and rainfall to dispersal and disease was investigated. Disease incidence and mortality were assessed in June and September each year for 3 or 4 years depending on plot. Phytophthora root rot as estimated by mortality counts over time in a logistic regression model progressed in only five of 19 plots over 3 years. None of the site parameters correlated with mortality data, although slightly more disease was found in plots with a north aspect. Rainfall was below normal in the 3 years of the study and did not correlate with mortality in any year. Lack of disease progress in the majority of plots was attributed to drought conditions in the region. In the five plots where mortality increased over time, spatial analysis suggested an aggregated pattern of diseased plants. Aggregation was apparent but not very strong among nearest neighbors, but was considerably stronger among groups of trees within a local area. This aggregation within groups was stronger when larger group sizes were examined by beta-binomial analysis. A spatial analysis by distance indices method (SADIE) indicated the presence of secondary clusters occurring several meters away from the main focus. A stochastic model also was employed that indicated a combination of spatial processes were likely involved, specifically a tendency toward spread within a local area, but not necessarily to the nearest neighboring trees, combined with an influence of background inoculum that could not be accounted for within local areas and may have come from external sources. Thus, all sources of inoculum including infected planting stock, inoculum in soil, infected trees, and contaminated equipment were equally important in epidemics of Phytophthora root rot in Fraser fir and dispersal of P. cinnamomi.

scholarly journals Incidence of Phytophthora Root Rot of Fraser Fir in North Carolina and Sensitivity of Isolates of Phytophthora cinnamomi to Metalaxyl

Plant Disease ◽  
2000 ◽  
Vol 84 (6) ◽  
pp. 661-664 ◽  
Author(s):  
D. M. Benson ◽  
L. F. Grand
Keyword(s):  
North Carolina ◽  
Root Rot ◽  
Phytophthora Cinnamomi ◽  
Disease Incidence ◽  
The State ◽  
Systematic Sampling ◽  
Phytophthora Root Rot ◽  
Fraser Fir ◽  
Phytophthora Spp ◽  
Old Trees

A survey of Fraser fir Christmas trees in North Carolina for incidence of Phytophthora root rot was conducted during 1997 and 1998. Field sites (7- to 13-year-old trees) and nursery transplant beds (4- to 5-year-old trees) selected at random were surveyed based on foliar symptoms of Phytophthora root rot. Field sites were surveyed with a random transect method (>3,000 trees/field) or by counting all trees (<3,000 trees/field). Overall, incidence of Phytophthora root rot averaged 9% over the 58 field sites sampled, with a range of 0 to 75%. No relationship was found between number of years Fraser fir had been planted in the field site and disease incidence. Disease incidence did not increase as field sites were rotated through second or third crops of Fraser fir. Phytophthora spp. were recovered from 1.8% of asymptomatic trees sampled from 58 field sites across the state. P. cinnamomi accounted for 91% of the Phytophthora isolates recovered. In nursery transplant beds where a systematic sampling procedure was used, incidence of diseased trees averaged 2%, with a range of 0 to 12% across 16 locations. Recovery of Phytophthora spp. averaged 1.2% from root samples collected from 50 asymptomatic seedlings at each location. Isolates collected from the field and nursery transplant beds were grown on cornmeal agar incorporated with 0, 1, 1.25, 10, or 100 μg a.i. metalaxyl/ml. All 166 isolates of P. cinnamomi tested were sensitive to metalaxyl at 1 or 1.25 μg a.i. metalaxyl/ml. Although incidence of Phytophthora root rot has not increased in the state compared to a survey done in 1976 to 1977, the disease continues to limit production of Fraser fir in North Carolina.

Control of Phytophthora Root Rot in Field Plantings of Fraser Fir with Fosetyl-Al and Mefenoxam

2006 ◽  
Vol 7 (1) ◽  
pp. 25 ◽  
Author(s):  
D. M. Benson ◽  
J. R. Sidebottom ◽  
J. Moody
Keyword(s):  
Root Rot ◽  
Tree Mortality ◽  
Phytophthora Cinnamomi ◽  
Flood Plain ◽  
Treatment Programs ◽  
Phytophthora Root Rot ◽  
Rainfall Events ◽  
Fraser Fir ◽  
Growing Seasons ◽  
Western North Carolina

Fungicides were evaluated for control of Phytophthora root rot for five growing seasons in two field plantings of Fraser fir (Abies fraseri) affected by Phytophthora cinnamomi in western North Carolina. At the first site, which had a fairly well-drained soil, treatment programs with Aliette (5 lb/100 gal, three applications per year), Subdue Maxx (3.7 fl oz/1.15 gal/1000 ft2, two applications per year), and Subdue GR (5.75 lb/1000 ft2, two applications per year) maintained low rates of mortality (< 10%) for three growing seasons, whereas tree mortality in the untreated plots reached 13 and 37% by the second and third growing seasons, respectively. At the second site, which was in a flood plain, disease did not develop during the first 2.5 years, even in untreated control plots. However, mortality increased rapidly following several high-rainfall events, but none of the fungicides had any effect on disease development. Apparently, at least under conditions not overly conducive to the disease, the fungicide treatment programs can delay the onset of high mortality rates caused by P. cinnamomi in Fraser fir for up to three growing seasons. Accepted for publication 23 February 2006. Published 31 March 2006.

scholarly journals Synergistic effects of a cellulase-producing Micromonospora carbonacea and an antibiotic-producing Streptomyces violascens on the suppression of Phytophthora cinnamomi root rot of Banksia grandis

1996 ◽  
Vol 74 (4) ◽  
pp. 618-624 ◽  
Author(s):  
Khaled A. El-Tarabily ◽  
Melissa L. Sykes ◽  
Ipek D. Kurtböke ◽  
Giles E. St. J. Hardy ◽  
Aneli M. Barbosa ◽  
...  
Keyword(s):  
Root Rot ◽  
Phytophthora Cinnamomi ◽  
Synergistic Effects ◽  
Control Plant ◽  
Pathogenic Fungi ◽  
Plant Pathogenic Fungi ◽  
Selective Isolation ◽  
Phytophthora Root Rot ◽  
Mine Site ◽  
Isolation Techniques

Three polyvalent Streptomyces phages were used to isolate four Micromonospora species (M. carbonacea, M. chalcea, M. purpureochromogenes, and M. inositola) from mine-site rhizosphere soils in Western Australia. Streptomyces violascens was isolated using selective isolation techniques from the same soils. The Micromonspora spp. were examined for their ability to produce cellulases. Micromonospora carbonacea, M. chalcea, and M. purpureochromogenes, which were found to produce the enzyme, caused lysis of Phytophthora cinnamomi hyphae. Glasshouse trials showed that the use of the cellulase-producing M. carbonacea isolate, in conjunction with the antibiotic-producing S. violascens isolate, had a synergistic effect on the suppression of the Phytophthora root rot and in promoting growth of Banksia grandis. The importance of using a number of antagonists with different antagonistic abilities to control plant pathogenic fungi is discussed. Keywords: biological control, Micromonospora carbonacea, Streptomyces violascens, cellulases, Phytophthora cinnamomi.

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