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 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 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.

Pathogenicity of Pythium spp. And Phytopththora drechsleri to Eucalyptus spp

1974 ◽  
Vol 22 (4) ◽  
pp. 661 ◽  
Author(s):  
GC Marks ◽  
FY Kassaby
Keyword(s):  
Root Rot ◽  
Phytophthora Cinnamomi ◽  
Pythium Ultimum ◽  
Pythium Species ◽  
Marked Contrast ◽  
Small Juvenile ◽  
Eucalypt Forest ◽  
Stage Of Development ◽  
Eastern Australia ◽  
Phytophthora Drechsleri

A number of Pythium spp, and Phytophthora drechsleri have been associated with Phytophthora cinnamomi in the die-back disease of eucalypts in forests of southern and eastern Australia. Although P. cinnamomi is generally considered to be the most important pathogen causing root rot and die-back, there is some uncertainty whether it is the only pathogen. The pathogenicity of Pythium ultimum, P. irregulare, P. debaryanum, P. vexans, P. mamillatum, three unidentified Pythium species from eucalypt forest soil and Phytophthora drechsleri was compared with that of Phytophthora cinnamomi on juvenile and intermediate-aged seedlings of Eucalyptus sieberi and juvenile seedlings of other eucalypt species. Of the Pythiums, only P. ultimum, P. irregulare and P. debaryanum could kill small juvenile seedlings at the two-leaf stage of development. Neither any of the Pythiums nor Phytophthora drechsleri could kill E. sieberi at the intermediate growth stage. In marked contrast, Phytophthora cinnamomi showed considerable pathogenicity, killing seedlings and saplings with rapidity. The unidentified Pythium spp, from native forests were completely innocuous.

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 Screening a Natural Product-Inspired Library for Anti-Phytophthora Activities

Molecules ◽  
2021 ◽  
Vol 26 (7) ◽  
pp. 1819
Author(s):  
Scott A. Lawrence ◽  
Hannah F. Robinson ◽  
Daniel P. Furkert ◽  
Margaret A. Brimble ◽  
Monica L. Gerth
Keyword(s):  
Natural Product ◽  
Root Rot ◽  
Mycelial Growth ◽  
Phytophthora Cinnamomi ◽  
Phytophthora Species ◽  
Front Line ◽  
Invasive Pathogens ◽  
Chemical Treatments ◽  
Ic50 Values ◽  
Inhibition Studies

Phytophthora is a genus of microorganisms that cause devastating dieback and root-rot diseases in thousands of plant hosts worldwide. The economic impact of Phytophthora diseases on crops and native ecosystems is estimated to be billions of dollars per annum. These invasive pathogens are extremely difficult to control using existing chemical means, and the effectiveness of the few treatments available is being jeopardized by increasing rates of resistance. There is an urgent need to identify new chemical treatments that are effective against Phytophthora diseases. Natural products have long been regarded as “Nature’s medicine chest”, providing invaluable leads for developing front-line drugs and agrochemical agents. Here, we have screened a natural product-inspired library of 328 chemicals against two key Phytophthora species: Phytophthora cinnamomi and Phytophthora agathidicida. The library was initially screened for inhibition of zoospore germination. From these screens, we identified twenty-one hits that inhibited germination of one or both species. These hits were further tested in mycelial growth inhibition studies to determine their half-maximal inhibitory concentrations (IC50s). Four compounds had IC50 values of approximately 10 µM or less, and our best hit had IC50s of approximately 3 µM against both Phytophthora species tested. Overall, these hits may serve as promising leads for the development of new anti-Phytophthora agrochemicals

The challenges of managing Phytophthora root rot in the nursery industry

2021 ◽  
Author(s):  
Jerry E Weiland
Keyword(s):  
Disease Control ◽  
Root Rot ◽  
Phytophthora Species ◽  
Control Measures ◽  
Community Members ◽  
Phytophthora Root Rot ◽  
Severe Problem ◽  
Successful Control ◽  
The Individual ◽  
Intensive Sampling

For nearly 100 years, Phytophthora root rot (PRR) has been a severe problem in nurseries. Early surveys found only one or two Phytophthora species on any one host. However, recent surveys show that nurseries are impacted by increasingly complex Phytophthora communities that vary by host, nursery, and region. Individual community members have diverse biological characteristics and differ in their responses to disease control measures. These differences may shift community composition towards members that are less sensitive to treatment, thereby decreasing overall disease control. Together, this suggests that PRR is better approached as a disease complex rather than as a disease caused by a single entity. Yet, most experiments use only a single Phytophthora isolate and therefore overlook the potential for other community members to be less responsive to treatment. Successful control is further limited by a lack of data on the disease losses and soilborne inoculum levels encountered in the nursery industry, which are essential for establishing risks for infection, pathogen movement, and for evaluating disease control efficacy. Focused surveys with intensive sampling are needed to better characterize the Phytophthora communities occurring on major nursery crops. Experiments should utilize a representative set of species and isolates to ensure treatments are effective. The presence of diverse Phytophthora communities in the nursery industry makes it less likely that any one disease control tactic will be broadly effective. Instead, a combination of approaches that take into account the individual weaknesses of each community member will likely be necessary to achieve long-term PRR control.

Phytophthora Species Differ in Response to Phosphorous Acid and Mefenoxam for the Management of Phytophthora Root Rot in Rhododendron

Plant Disease ◽  
2020 ◽  
Author(s):  
Jerry E. Weiland ◽  
Carolyn F. Scagel ◽  
Niklaus J. Grünwald ◽  
E. Anne Davis ◽  
Bryan R. Beck
Keyword(s):  
Root Rot ◽  
Production Systems ◽  
Foliar Spray ◽  
Phosphorous Acid ◽  
Phytophthora Species ◽  
Phytophthora Root Rot ◽  
Application Method ◽  
Affect Control ◽  
Pathogen Diversity ◽  
Significant Disease

Phytophthora root rot, caused by many soilborne Phytophthora species, is a significant disease affecting the $42 million rhododendron nursery industry. Rhododendron growers have increasingly reported failure by two systemic fungicides, phosphorous acid and mefenoxam, to adequately control root rot. Both fungicides may be applied as a foliar spray or soil drench, but it is unknown how application method, fungicide chemistry, or pathogen diversity affects disease control. Therefore, two experiments were conducted to (i) determine whether differences in application method or fungicide chemistry affect control of root rot caused by P. cinnamomi and P. plurivora and (ii) evaluate the sensitivity of Phytophthora species and isolates from the rhododendron industry to each fungicide. Results demonstrated that soil drenches of either fungicide were more effective than foliar sprays for control of P. cinnamomi, but were ineffective for P. plurivora. Furthermore, Phytophthora species and isolates varied in sensitivity to phosphorous acid and mefenoxam, and there were multiple fungicide insensitive isolates, especially within P. plurivora. Differences in sensitivity were also observed among isolates from different nurseries and production systems, with some nurseries having less sensitive isolates than others and with container systems generally having less sensitive isolates than field systems. Our results provide three potential reasons for why fungicide control of Phytophthora root rot might fail: (i) the fungicide can be applied to the wrong portion of the plant for optimal control, (ii) there are differences in fungicide sensitivity among soilborne Phytophthora species and isolates infecting rhododendron, and (iii) fungicide insensitive isolates are present in the rhododendron nursery industry.

scholarly journals Environmental assessment of the Tung cultivation through life cycle analysis

2014 ◽  
Vol 3 (1) ◽  
pp. 70 ◽  
Author(s):  
Marcelo Bern�l ◽  
Rosana Schneider ◽  
�nio Machado
Keyword(s):  
Life Cycle ◽  
Production Systems ◽  
Life Cycle Management ◽  
Assessment Method ◽  
Agroforestry Systems ◽  
Family Farms ◽  
Conventional Agriculture ◽  
The Past ◽  
Ecosystem Changes ◽  
Poor Soil

Over the past few decades, conventional agriculture has been facing serious crises caused by numerous factors, including poor soil management and the excessive application of pesticides. Thus, alternative production systems have been developed, including agroforestry systems, especially those that produce both energy and food. The objective of this study was to environmentally evaluate the culture of Aleurites fordii Hemls. (Tung) using the Life Cycle Assessment method with the SimaPro 7.3.2 software. The results revealed that in family farms that use less mechanization to harvest crops, the primary category of environmental impact was land use, which included the removal of animal and vegetable species and ecosystem changes. The full impact of this category was 1741.21 m2yr PDF (potentially disappeared fraction). Subsequently, prognostics were established for the reduction of such impacts, and we conclude that Tung has a high potential for agricultural installation with high responsibility to the environment. Keywords: Environmental factors, Aleurites fordii Hemls, Life Cycle Management, Tung.

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.

Identification of Pythium species as pathogens of garlic root rot

2021 ◽  
Author(s):  
Bo Zhang ◽  
Yueli Zhang ◽  
Liguo Ma ◽  
Kai Qi ◽  
Peng Wang ◽  
...  
Keyword(s):  
Root Rot ◽  
Pythium Species
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