The Use of qPCR Reveals a High Frequency of Phytophthora quercina in Two Spanish Holm Oak Areas

The struggling Spanish holm oak woodland situation associated with Phytophthora root rot has been studied for a long time. Phytophthora cinnamomi is considered the main, but not the only species responsible for the decline scenario. This study verifies the presence and/or detection of Phytophthora species in two holm oak areas of Spain (southwestern “dehesas” and northeastern woodland) using different isolation and detection approaches. Direct isolation and baiting methods in declining and non-declining holm oak trees revealed Phytophthora cambivora, Phytophthora cinnamomi, Phytophthora gonapodyides, Phytophthora megasperma, and Phytophthora pseudocryptogea in the dehesas, while in the northeastern woodland, no Phytophthora spp. were recovered. Statistical analyses indicated that there was not a significant relationship between the Phytophthora spp. isolation frequency and the disease expression of the holm oak stands in the dehesas. Phytophthora quercina and P. cinnamomi TaqMan real-time PCR probes showed that both P. cinnamomi and P. quercina are involved in the holm oak decline in Spain, but P. quercina was detected in a higher frequency than P. cinnamomi in both studied areas. Thus, this study demonstrates that molecular approaches complement direct isolation techniques in natural and seminatural ecosystem surveys to determine the presence and distribution of Phytophthora spp. This is the first report of P. pseudocryptogea in Europe and its role in the holm oak decline should be further studied.

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Vegetative Propagation of Phytophthora cinnamomi-Tolerant Holm Oak Genotypes by Axillary Budding and Somatic Embryogenesis

Forests ◽

10.3390/f11080841 ◽

2020 ◽

Vol 11 (8) ◽

pp. 841

Author(s):

Maria Teresa Martínez ◽

Francisco Javier Vieitez ◽

Alejandro Solla ◽

Raúl Tapias ◽

Noelia Ramírez-Martín ◽

...

Keyword(s):

Somatic Embryogenesis ◽

Somatic Embryos ◽

Phytophthora Cinnamomi ◽

Shoot Proliferation ◽

Holm Oak ◽

Induction Medium ◽

Axillary Shoot ◽

Oak Decline ◽

Shoot Cultures

Holm oak (Quercus ilex) is one of the most widely distributed tree species in the Mediterranean basin. High mortality rates have been observed in holm oak populations in the southwest of the Iberian Peninsula as a result of oak decline syndrome. Selection and propagation of genotypes tolerant to this syndrome could aid the restoration of affected areas. In this article, we report micropropagation and conservation procedures based on axillary budding and somatic embryogenesis (SE) of holm oak plants, selected for their tolerance to Phytophthora cinnamomi—the main biotic factor responsible for oak decline. Forced shoots were obtained from potted plants of eight different genotypes, and used as stock material to establish in vitro shoot proliferation cultures. Reliable shoot proliferation was obtained in seven out the eight genotypes established in vitro, whereas multiplication rates were genotype-dependent. The highest rooting rates were obtained by culturing shoots for 24 h or 48 h on rooting induction medium containing 25 mg L−1 indole-3-butyric acid, followed by transfer to medium supplemented with 20 µM silver thiosulphate. Axillary shoot cultures can be successful conserved by cold storage for 12 months at 4 °C under dim lighting. Shoot tips, excised from axillary shoot cultures established from tolerant plants, were used as initial explants to induce SE. Somatic embryos and/or nodular embryogenic structures were obtained on induction medium with or without indole-acetic acid 4 mg L−1, in two out the three genotypes evaluated, and induction rates ranged between 2 and 4%. Plantlet recovery was 45% after two months cold stratification of somatic embryos and eight weeks of culture on germination medium. Vegetative propagation of P. cinnamomi-tolerant Q. ilex trees is a valuable milestone towards the restoration of disease-affected areas.

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

Plant Disease ◽

10.1094/pdis-04-18-0666-re ◽

2018 ◽

Vol 102 (12) ◽

pp. 2560-2570 ◽

Cited By ~ 4

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.

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

Plant Disease ◽

10.1094/pdis.2000.84.6.661 ◽

2000 ◽

Vol 84 (6) ◽

pp. 661-664 ◽

Cited By ~ 19

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.

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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

Canadian Journal of Botany ◽

10.1139/b96-078 ◽

1996 ◽

Vol 74 (4) ◽

pp. 618-624 ◽

Cited By ~ 53

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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Phytophthora cinnamomi as a Contributor to White Oak Decline in Mid-Atlantic United States Forests

Plant Disease ◽

10.1094/pdis-06-13-0649-re ◽

2014 ◽

Vol 98 (3) ◽

pp. 319-327 ◽

Cited By ~ 20

Author(s):

M. E. McConnell ◽

Y. Balci

Keyword(s):

United States ◽

Fine Roots ◽

Phytophthora Cinnamomi ◽

United States Department ◽

Oak Decline ◽

White Oak ◽

Phytophthora Spp ◽

Oak Trees ◽

Root Health ◽

The Impact

To evaluate Phytophthora cinnamomi as a cause of white oak (Quercus alba) decline in mid-Atlantic forests, sampling was conducted at 102 sites from 2011 to 2012. Soil and roots from healthy and declining white oak trees were collected. Phytophthora spp. were isolated using baiting and CFU of P. cinnamomi quantified using wet-sieving. Fine roots were scanned and measured. Phytophthora spp. were isolated from 43% of the sites. P. cinnamomi was common; six other species were isolated infrequently. Little difference in lesion size existed on white oak seedlings inoculated with 32 isolates of P. cinnamomi; only 13 isolates caused significant mortality. Soils from white oak versus nine other hosts did not have significantly different CFU. P. cinnamomi was restricted to United States Department of Agriculture hardiness zones six and seven and never found in zone five. The presence of Phytophthora spp. in soil can be associated with white oak fine root health. When Phytophthora spp. were present, white oak trees in zones five and six had less fine roots. In mid-Atlantic oak forests, however, environmental conditions appear to play a key role in determining the impact of P. cinnamomi on the root system. P. cinnamomi alone does not appear to be a causal factor of white oak decline.

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

Plant Disease ◽

10.1094/pdis-09-20-1873-re ◽

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.

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The Involvement of Phytophthora Root Rot and Drought Stress in Holm Oak Decline: from Ecophysiology to Microbiome Influence

Current Forestry Reports ◽

10.1007/s40725-019-00105-3 ◽

2019 ◽

Vol 5 (4) ◽

pp. 251-266 ◽

Cited By ~ 3

Author(s):

Francisco José Ruiz-Gómez ◽

Alejandro Pérez-de-Luque ◽

Rafael María Navarro-Cerrillo

Keyword(s):

Drought Stress ◽

Root Rot ◽

Holm Oak ◽

Oak Decline ◽

Phytophthora Root Rot

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Factores ambientales en la distribución de la seca en la encina (Quercus ilex subsp. ballota) = Environmental Variables in the Distribution of La Seca Disease in the Holm Oak (Quercus Ilex Subsp. Ballota)

Espacio Tiempo y Forma Serie VI Geografía ◽

10.5944/etfvi.11.2018.21777 ◽

2018 ◽

pp. 107

Author(s):

Mario Corral Ribera ◽

Concepción Fidalgo Hijano ◽

Begoña Peco Vázquez

Keyword(s):

Environmental Variables ◽

Quercus Ilex ◽

Phytophthora Cinnamomi ◽

Abiotic Factors ◽

Information Criteria ◽

Holm Oak ◽

Oak Decline ◽

Topographic Wetness Index ◽

Daphne Gnidium ◽

Field Samples

La combinación de factores bióticos y abióticos (clima, orografía, litología, competencia interespecífica, etc.) y la patogenicidad de agentes como el hongo Phytophthora cinnamomi Rands han generado la enfermedad fitosanitaria denominada en España como la seca de encinas y alcornoques de la Península Ibérica. El objetivo del presente estudio es el análisis que desempeñan las variables ambientales en el desarrollo de dicha enfermedad y determinar cuáles tienen una mayor influencia en su propagación. Se toma como área de estudio el Monte de Valdelatas, Alcobendas, Madrid (hoja 534 del Mapa Topográfico Nacional a escala 1:50.000. Coordenadas UTM X: X: 442592.51, Y: 4487266.63 zona 30T). Se obtivieron muestras en campo de 100 árboles de Quercus ilex subsp. ballota (50 con apariencia saludable y 50 con síntomas aparentes de enfermedad) azarosamente ubicados en 7 transectos. En relación al modelo estadístico se empleó un modelo binomial cuya variable respuesta se definió como sano/enfermo, según la apariencia del árbol. Así mismo, se manejó el Criterio de Información de Akaike (AIC) con el fin de establecer el mejor modelo. En su caso, presentando un 44% de la varianza (D2 = 0.437) y un valor de 89.68 en AIC. Las principales variables ambientales que interfieren en la enfermedad fueron: proximidad a cursos fluviales, índice de humedad topográfico, cobertura de Daphne gnidium y Quercus ilex subsp. ballota y la edad de los individuos muestreados. Dada la pérdida en la masa forestal de Quercus debido a la enfermedad de la seca, es necesario comprender el comportamiento de dicha enfermedad, así como conocer los factores ambientales que contribuyen a su expansión, pudiendo llegar de tal modo a identificar algún factor inhibidor. The combination of biotic and abiotic factors (climate, orography, lithology, interspecific competition, etc.) and the pathogenicity of agents such as the fungus Phytophthora cinnamomi Rands has generated the phytosanitary disease known as the oak decline (la seca) in holm oak and cork oak stand of the Iberian Peninsula. The aim of this study is to analyse the role played by environmental variables in the development of this disease, and to determine which have a stronger influence in the spread of the disease. Data has been obtained from Monte de Valdelatas, Alcobendas, Madrid (sheet 534 national topographic map, scale 1:50.000, UTM coordinates X: 442592.51, Y: 4487266.63 zone 30T). Field samples were taken from 100 randomly selected Quercus ilex subsp. ballota individuals (50 with a healthy appearance and 50 that showed disease symptoms), located within 7 transects. In relation to the statistical model, in this work a binomial model was used. On it, the response variable was defined as healthy/unhealthy, depending on the appearance of each tree. Akaike Information Criteria (AIC) was used to define the quality of the model. We selected model obtained a score of 89.68 and accounts for approximately 44% of data variability (D2 = 0,437). The main environmental variables that impact disease were: proximity to river course, topographic wetness index, cover of Daphne gnidium and Quercus ilex subsp. ballota, and the age of the individuals. Given the loss of Quercus forest mass caused by the spread of the oak decline disease, detected in several countries, including Spain, it becomes necessary to adequately understand the different factors that contribute and, in some cases, is the cause of the expansion of the disease, as well as to identify any inhibiting factors.

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Effects of Fuel Reduction Treatments on Incidence of Phytophthora Species in Soil of a Southern Appalachian Mountain Forest

Plant Disease ◽

10.1094/pdis-07-10-0505 ◽

2011 ◽

Vol 95 (7) ◽

pp. 811-820 ◽

Cited By ~ 7

Author(s):

I. M. Meadows ◽

D. C. Zwart ◽

S. N. Jeffers ◽

T. A. Waldrop ◽

W. C. Bridges

Keyword(s):

Prescribed Burning ◽

Phytophthora Cinnamomi ◽

Phytophthora Species ◽

Mountain Forest ◽

Fuel Reduction ◽

Appalachian Mountain ◽

Phytophthora Spp ◽

Southern Appalachian ◽

Southern Appalachian Mountain ◽

Mountain Laurel

The National Fire and Fire Surrogate Study was initiated to study the effects of fuel reduction treatments on forest ecosystems. Four fuel reduction treatments were applied to three sites in a southern Appalachian Mountain forest in western North Carolina: prescribed burning, mechanical fuel reduction, mechanical fuel reduction followed by prescribed burning, and a nontreated control. To determine the effects of fuel reduction treatments on Phytophthora spp. in soil, incidences were assessed once before and twice after fuel reduction treatments were applied. Also, the efficiency of the baiting bioassay used to detect species of Phytophthora was evaluated, and the potential virulence of isolates of Phytophthora spp. collected from forest soils was determined. Phytophthora cinnamomi and P. heveae were the only two species recovered from the study site. Incidences of these species were not significantly affected by fuel reduction treatments, but incidence of P. cinnamomi increased over time. In the baiting bioassay, camellia leaf disks were better than hemlock needles as baits. P. cinnamomi was detected best in fresh soil, whereas P. heveae was detected best when soil was air-dried and remoistened prior to baiting. Isolates of P. heveae were weakly virulent and, therefore, potentially pathogenic—causing lesions only on wounded mountain laurel and rhododendron leaves; however, isolates of P. cinnamomi were virulent and caused root rot and mortality on mountain laurel and white pine plants.

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Phytophthora Species in Soils Associated with Declining and Nondeclining Oaks in Missouri Forests

Plant Disease ◽

10.1094/pdis-91-5-0633a ◽

2007 ◽

Vol 91 (5) ◽

pp. 633-633 ◽

Cited By ~ 7

Author(s):

B. W. Schwingle ◽

J. Juzwik ◽

J. Eggers ◽

B. Moltzan

Keyword(s):

United States ◽

The United States ◽

Selective Medium ◽

Phytophthora Species ◽

Oak Decline ◽

Eastern United States ◽

Contributing Factors ◽

Phytophthora Spp ◽

Agar Plug ◽

Stem Lesions

Periodic episodes of oak decline have occurred in the Missouri Ozark forests since the early 1900s and the disease is currently severe (2). Several Phytophthora spp. contribute to oak decline in Europe (1), but the role of Phytophthora spp. in oak decline in the eastern United States is not known. Mineral soils collected around the bases of declining and nondeclining oaks in paired sites in central Missouri forests were assayed for the presence of these taxa by baiting flooded soil with Quercus robur leaves. Q. rubra and Q. velutina were the oak species on three sites and Q. alba was on the fourth. Isolates from symptomatic baits plated on PARPNH selective medium were identified tentatively on classical taxonomic characteristics. Five isolates of P. cambivora, two of P. quercina, and eight of P. cinnamomi were obtained from soils around one, one, and three trees, respectively, on decline sites. The internal transcribed spacer sequences for each isolate were compared to those in GenBank; BLAST searches for all isolates had nucleotide identities of 99% and E values of 0, which confirmed the identifications. Greenhouse pot trials were conducted to assess pathogenicity of isolates on stems of 2-year-old Q. alba and Q. rubra. A mycelial agar plug was inserted into a 1-cm long slit cut into the cambium 5 cm above the root collar and covered with sterile, moist cotton and wrapped with laboratory film. The treatments included two isolates of P. cambivora, one of P. quercina, three of P. cinnamomi, and a sterile agar plug. Each host × isolate combination was replicated four times, and the experiment was conducted twice in the greenhouse (natural lighting; temperature ≤32°C in summer and ≥7°C in winter). Stem lesions were produced commonly by P. cambivora (28 of 32 seedlings) and P. cinnamomi (46 of 48 seedlings) within 3 months; none was found on control seedlings or those inoculated with P. quercina. Mean lengths (cm) of lesions caused by P. cinnamomi were greater for Q. rubra (5.6) than for Q. alba (4.3) and lesion lengths for P. cambivora were greater for Q. alba (5.2) than for Q. rubra (4.4). Seven Q. alba seedlings inoculated with P. cambivora and one Q. alba inoculated with P. cinnamomi died before 3 months. All Phytophthora species were recovered from inoculated stems at 3 months except that P. quercina was not recovered in one trial. To our knowledge, this is the first report of Phytophthora species in soils of Missouri oak forests, of P. quercina in the United States, and of the ability of P. cambivora to cause stem lesions on Q. alba. P. cinnamomi and P. cambivora should be investigated in situ as possible contributing factors of oak decline in Missouri. References: (1) T. Jung et al. Plant Pathol. 49:706, 2000. (2) R. Lawrence et al. MO. Conserv. 63:11, 2002.

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