Incidence of Phytophthora species in oak forests in Austria and their possible involvement in oak decline

Five Phytophthora species comprising a total of 243 isolates (77 P. cinnamomi, 23 P. citrophthora, 18 P. multivora, 18 P. pini, and 107 P. plurivora) were screened for sensitivity to mefenoxam, fosetyl-Al, dimethomorph, dimethomorph + ametoctradin and fluoxastrobin using amended agar assays. Mefenoxam-insensitive isolates were detected within P. cinnamomi (4%), P. multivora (11%), and P. plurivora (12%) even at approximately 2.5x the recommended label rate. These isolates were also insensitive to higher (off-label) concentrations of fluoxastrobin. Concentrations of dimethomorph (400 g/mL) and dimethomorph + ametoctradin (100 g/mL) were mostly effective in mycelial growth inhibition, but two P. plurivora isolates were insensitive, suggesting that resistance management is required. All mefenoxam-insensitive isolates were sensitive to fosetyl-Al at the label rate. Surprisingly, the populations of P. cinnamomi from mid-Atlantic oak forests included insensitive isolates. With almost all species, isolates recovered from asymptomatic hosts (e.g., soil/potting media collected of randomly selected asymptomatic hosts) had a significantly greater relative growth rate when compared to isolates recovered from symptomatic hosts (e.g., isolates recovered from lesions or wilted plants). These findings suggest that mefenoxam should no longer be used to manage oomycetes in Maryland ornamental nurseries and that the use of fluoxastrobin should be limited.

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An Overview of Phytophthora Species Inhabiting Declining Quercus suber Stands in Sardinia (Italy)

Forests ◽

10.3390/f11090971 ◽

2020 ◽

Vol 11 (9) ◽

pp. 971

Author(s):

Salvatore Seddaiu ◽

Andrea Brandano ◽

Pino Angelo Ruiu ◽

Clizia Sechi ◽

Bruno Scanu

Keyword(s):

Rhizosphere Soil ◽

Phytophthora Cinnamomi ◽

Stream Water ◽

Morphological Characters ◽

Quercus Suber ◽

Phytophthora Species ◽

Cork Oak ◽

Oak Forests ◽

Primary Role ◽

Ecological Value

Cork oak forests are of immense importance in terms of economic, cultural, and ecological value in the Mediterranean regions. Since the beginning of the 20th century, these forests ecosystems have been threatened by several factors, including human intervention, climate change, wildfires, pathogens, and pests. Several studies have demonstrated the primary role of the oomycete Phytophthora cinnamomi Ronds in the widespread decline of cork oaks in Portugal, Spain, southern France, and Italy, although other congeneric species have also been occasionally associated. Between 2015 and 2019, independent surveys were undertaken to determine the diversity of Phytophthora species in declining cork oak stands in Sardinia (Italy). Rhizosphere soil samples were collected from 39 declining cork oak stands and baited in the laboratory with oak leaflets. In addition, the occurrence of Phytophthora was assayed using an in-situ baiting technique in rivers and streams located throughout ten of the surveyed oak stands. Isolates were identified by means of both morphological characters and sequence analysis of internal transcribed spacer (ITS) regions of ribosomal DNA. In total, 14 different Phytophthora species were detected. Phytophthora cinnamomi was the most frequently isolated species from rhizosphere soil, followed by P. quercina, P. pseudocryptogea, and P. tyrrhenica. In contrast, P. gonapodyides turned out to be the most dominant species in stream water, followed by P. bilorbang, P. pseudocryptogea, P. lacustris, and P. plurivora. Pathogenicity of the most common Phytophthora species detected was tested using both soil infestation and log inoculation methods. This study showed the high diversity of Phytophthora species inhabiting soil and watercourses, including several previously unrecorded species potentially involved in the decline of cork oak forests.

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Developing a Stand Hazard Index for Oak Decline in Upland Oak Forests of the Ozark Highlands, Missouri

Northern Journal of Applied Forestry ◽

10.1093/njaf/28.1.19 ◽

2011 ◽

Vol 28 (1) ◽

pp. 19-26 ◽

Cited By ~ 6

Author(s):

Zhaofei Fan ◽

Xiuli Fan ◽

Martin A. Spetich ◽

Stephen R. Shifley ◽

W. Keith Moser ◽

...

Keyword(s):

Tree Mortality ◽

Survival Rates ◽

Hazard Index ◽

Classification And Regression Tree ◽

Tree Level ◽

Oak Forests ◽

Oak Decline ◽

White Oak ◽

Ozark Highlands ◽

Black Oak

Abstract Black oak (Quercus velutina Lam.) and scarlet oak (Quercus coccinea Muenchh.)—two major components (44% of total stand basal area) of upland oak forests—are suffering severe decline and mortality in the Ozark Highlands, Missouri. However, factors influencing their survival (mortality) are not well understood. In this study we quantified how stand and tree-level predisposing factors are associated with survival of black and scarlet oaks. Sixteen-year monitoring data from the Missouri Ozark Forest Ecosystem Project (MOFEP) indicated that overall annual mortality of black and scarlet oaks averaged 2.2 and 1.7%, respectively, three to five times higher than expected (around 0.5%) for white oak, a common associate. For the first 8 years of the study (1990‐1998), survival rates of black and scarlet oaks were similar. Thereafter, the survival rate of black oak declined relative to scarlet oak. Using the classification and regression tree (CART) method we classified black oak and scarlet oak trees into seven and nine risk groups, respectively, that differed significantly in rates of tree mortality. Groups were distinguished based on tree diameter, crown class, and size relative to competitors. An oak decline and mortality hazard index was thus developed as the weighted means of risk group mortality, which can help managers prescribe species-specific silvicultural treatments to help mitigate oak decline and associated mortality.

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Zoning of Areas with Susceptibility to Oak Decline in Western Iran

Quaestiones Geographicae ◽

10.2478/quageo-2021-0006 ◽

2021 ◽

Vol 0 (0) ◽

Author(s):

Mohadeseh Ghanbari Motlagh ◽

Masoud Kiadaliri

Keyword(s):

Slope Aspect ◽

Oak Forests ◽

Oak Decline ◽

Effective Parameters ◽

Western Iran ◽

Forest Density ◽

Temperature And Precipitation ◽

Zagros Forests ◽

Rapid Action ◽

Overlap Method

Abstract Zagros forests have the greatest impact on soil and water protection in western Iran. Despite this, a significant part of these forests, especially in Ilam province, have suffered a lot due to the phenomenon of oak decline. The first and most fundamental thing a person must know when combating this issue is the distribution of these areas in forests. Therefore, using the parameters affecting the decline in the forests of Ilam province and based on fuzzy logic, a map of susceptible to oak decline areas was prepared. In this study, the parameters of temperature and precipitation, slope, aspect, altitude, distance from farmlands, roads and forest density were selected as effective parameters and fuzzy gamma overlap method was used. The results showed that more than 77% of the oak forests in the province are highly and extremely susceptible to the decline. This confirms the need for rapid action to plan and protect these forests. In addition, the fuzzy method is proposed, which is considered as a fast and efficient method in preparing such maps for other areas.

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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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Phytophthora species and oak decline - can a weak competitor cause significant root damage in a nonsterilized acidic forest soil?

New Phytologist ◽

10.1111/j.1469-8137.2004.01016.x ◽

2004 ◽

Vol 162 (1) ◽

pp. 211-222 ◽

Cited By ~ 27

Author(s):

Ulrika Jonsson

Keyword(s):

Forest Soil ◽

Phytophthora Species ◽

Oak Decline ◽

Root Damage ◽

Weak Competitor

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Endemic and Emerging Pathogens Threatening Cork Oak Trees: Management Options for Conserving a Unique Forest Ecosystem

Plant Disease ◽

10.1094/pdis-03-16-0408-fe ◽

2016 ◽

Vol 100 (11) ◽

pp. 2184-2193 ◽

Cited By ~ 27

Author(s):

Salvatore Moricca ◽

Benedetto T. Linaldeddu ◽

Beatrice Ginetti ◽

Bruno Scanu ◽

Antonio Franceschini ◽

...

Keyword(s):

Mediterranean Basin ◽

Rural Landscape ◽

Cork Oak ◽

Oak Forests ◽

Oak Decline ◽

Primary Role ◽

Emerging Pathogens ◽

Management Options ◽

Oak Trees ◽

Cork Production

Cork oak (Quercus suber) forests are economically and culturally intertwined with the inhabitants of the Mediterranean basin and characterize its rural landscape. These forests cover over two million hectares in the western Mediterranean basin and sustain a rich biodiversity of endemisms as well as representing an important source of income derived from cork production. Currently cork oak forests are threatened by several factors including human-mediated disturbances such as poor or inappropriate management practices, adverse environmental conditions (irregular water regime with prolonged drought periods), and attacks of pathogens and pests. All these adverse factors can interact, causing a complex disease commonly known as “oak decline.” Despite the numerous investigations carried out so far, decline continues to be the main pathological problem of cork oak forests because of its complex etiology and the resulting difficulties in defining suitable control strategies. An overview of the literature indicates that several pathogenic fungi and oomycota can play a primary role in the etiology of this syndrome. Therefore, the aim of this review is to analyze the recent advances achieved regarding the bio-ecology of the endemic and emerging pathogens that threaten cork oak trees with particular emphasis on the species more directly involved in oak decline. Moreover, the effect of climate change on the host-pathogen interactions, a task fundamental for making useful decisions and managing cork oak forests properly, is considered.

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