Search Results (26)

The quarantine pathogen Phytophthora ramorum has a high potential for dispersal due to its airborne inoculum, its wide range of hosts, and its ability to spread through the trade of nursery plants. For these reasons, it represents a serious threat to ornamental nursery production and, consequently, to urban, natural and semi-natural ecosystems. This oomycete pathogen (EU1 lineage, A1 mating type) has been detected on Viburnum tinus in a commercial nursery located in the Pistoia nursery district (PND) (Tuscany, central Italy), one of the main nursery areas for the production of ornamentals in Europe. Artificial inoculations were carried out in the laboratory under controlled conditions, following a standard detached-leaf assay protocol, on leaves of 16 ornamental shrub species commonly marketed by the PND. Disease severity was assessed, and susceptibility categories (high, moderate, low, and non-susceptible) were defined based on data collected at 7 and 14 days post-inoculation and validated through statistical analysis. Inoculated species exhibited variable levels of disease severity. The results confirmed the pathogen’s high virulence on Viburnum tinus and Rhododendron hybrid ‘Madame Masson’. The following species were also found to be highly susceptible: Ilex aquifolium, Loropetalum chinense, Magnolia stellata, Osmanthus fragrans, and Trachelospermum jasminoides. Camellia japonica, Nerium oleander, Osmanthus heterophyllus, Prunus laurocerasus, and Rhododendron obtusum showed moderate susceptibility. Arbutus unedo, Laurus nobilis, Photinia fraseri and Syringa vulgaris exhibited low susceptibility. At the end of the trial, no infected species fell into the non-susceptible categories. The oomycete proved particularly aggressive on Ilex aquifolium, the most susceptible host among those tested. This high susceptibility is a new finding that could have significant epidemiological implications. Our findings emphasize the need for rigorous phytosanitary surveillance in nursery systems, based on constant monitoring and the adoption of high-throughput diagnostic protocols, in order to implement effective and rapid control measures. Full article

Phytophthora ramorum causes Sudden Oak Death, threatening global forests and nurseries. We modelled its current and future global distribution using an optimized MaxEnt model (mean AUC = 0.978). Temperature seasonality was the key driver (29.4%). Currently, suitable habitats (~42.48 million km²) concentrate in mid-latitude coastal regions (e.g., North America, Europe, East Asia). Future projections (SSP126-585) show no systematic contraction but rather significant spatial shifts: suitable areas expand poleward and upward in elevation while contracting in some current regions. High-suitability areas (5.52–6.40 million km²) change by −3% to +12%, with the centroid shifting northwestward, notably into the African Sahel under high emissions. Our findings indicate that, within the framework of the current modeling approach and the emission scenarios applied, climate warming is likely to lead to a net increase in the suitable habitat for this pathogen at the global scale, providing a critical scientific basis for the development of international phytosanitary strategies. Full article

Invasive Phytophthora species are increasingly impacting UK landscapes. Most recently, cryptic outbreaks of P. pluvialis Reeser, Sutton & E. Hansen have occurred on western hemlock and Douglas fir at several forest sites across Britain. To better understand the ubiquity and life cycle of this pathogen in British forests and the assemblages of co-inhabiting Phytophthora species, metabarcoding and baiting methodologies were applied to soil, stream water, and rainwater samples collected over a full calendar year from seventeen sites across Britain. Thirty-five Phytophthora species were detected across all sites, substrates, and detection methods, with most detections occurring in stream water by metabarcoding. The three most frequently detected species were (1) P. pluvialis, (2) P. gonapodyides H.E. Petersen & Buisman and (3) P. ramorum Werres, De Cock & Man in ‘t’ veld. Other species detected included the regulated pathogens P. austrocedri Greslen & Hansen, P. kernoviae Brasier, Beales & S.A. Kirk and P. lateralis Tucker & Milbraith, as well as P. ornamentata Scanu, Linald & T. Jung, a new species record for the UK. Phytophthora pluvialis was most frequently detected in March, with rainfall trap metabarcoding data suggesting that aerial dissemination occurs predominantly in late winter/early spring. Consistent detections of P. pluvialis in soil by metabarcoding indicate the potential for soilborne transfer of this pathogen by animal or human vectors, including equipment or machinery in forest operations. The study’s findings are discussed in relation to understanding how P. pluvialis spreads and the approaches needed to address key knowledge gaps in relation to inoculum sources. The results provide a baseline for Phytophthora diversity in British commercial forests, facilitating a greater understanding of typical and unusual trends in species assemblages. This study also consolidates the value of metabarcoding as an effective surveillance tool for Phytophthora in commercial forests. Full article

Coast Live Oak (Quercus agrifolia) is a native keystone hardwood species of the California coastal and semi-arid forest environment. Q. agrifolia is threatened by pathogens such as the oomycete Phytophthora ramorum, which is known to cause Sudden Oak Death in environments from Southern California to Oregon. This study considers oaks and their rootzone microbes recovering from moderate and low-intensity fires in rapid succession, compared to high- and low-intensity fires with a large time gap between them. cDNA libraries from nine oak leaf tissue samples were sequenced on DNBseq. Soil samples were sent out for shotgun metagenomics and for 16S community profiling. The de novo Q. agrifolia assembly yielded 521,817 transcripts with an average length of 805.2 bp. Among identified DEGs (differentially expressed genes) between the trail areas, several candidate genes were identified including shikimate dehydrogenase and myrcene synthase. The MegaBLAST results showed a high degree of similarity to WGS sequences from Q. agrifolia that had been previously annotated in other closely related Quercus species. There was a differential abundance of microbial genera associated with the different burn areas, including Pedobacter, Filimonas, Cohnella, and Sorangium. The data embody the first Q. agrifolia transcriptome that with further development could be used to screen oak seedlings for resistance; beneficial microbial populations have been identified that are associated with fire recovery under varied conditions. Full article

Phytophthora ramorum, the cause of Sudden Oak Death and related diseases, threatens over 130 tree and shrub species. We evaluated the biocontrol potential of isolates from nine Trichoderma species against P. ramorum using growth-rate studies, dual-culture assays, and culture-filtrate assays. Results showed significant variation in Trichoderma growth rates and biocontrol potential. Some isolates exhibited rapid growth, effective overgrowth, and lethal effects against P. ramorum and produced potent antagonistic metabolites. Faster growth rates only partially correlated with biocontrol efficacy, indicating that factors beyond growth, such as metabolite production, play significant roles. Notably, isolates of T. koningii, T. viride, and the commercial product SoilGard™ (T. virens) showed promising efficacy. We calculated a combined biocontrol variable to rank isolates based on vigour and efficacy to aid in identifying promising candidates. Our findings support the use of Trichoderma spp. as biocontrol agents against P. ramorum and underscore the need for a multifaceted approach to selecting and optimizing isolates. Our evaluation demonstrated the importance of using different assays to assess specific mechanisms of action of biocontrol candidates. Future research should further explore these interactions to enhance the sustainable management of P. ramorum. Full article

Phytopathogenic fungi are living organisms that cause plant diseases and great damage to agricultural products. Despite the wide range of commercial fungicide products in use, there is a clear need for new and environmentally friendly fungicides. Here we propose a new ecological fungicide, copper alginate microspheres prepared by ionic gelation. The microspheres were characterized (morphology and topography, encapsulation efficiency, loading capacity, swelling behavior, rheology, kinetics and mechanism of copper ions release) and their in vitro antifungal potential against selected genera of phytopathogenic fungi was evaluated. Copper alginate microspheres inhibited spore germination of Botrytis cinerea. Compared to the control, the inhibition of B. cinerea spore germination (48%) was greater than that of the commercial fungicide Neoram^® (22%). The mycelial growth of Cercospora beticola and Phytophthora ramorum was also significantly inhibited by the addition of copper alginate microspheres. Novel fungicide offer effective disease control while minimizing environmental impact and promoting sustainable agriculture practices. Full article

Fatty acid elongases play crucial roles in synthesizing long-chain polyunsaturated fatty acids. Identifying more efficient elongases is essential for enhancing oleaginous microorganisms to produce high yields of target products. We characterized three elongases that were identified with distinct specificities: McELO from Mucor circinelloides, PrELO from Phytophthora ramorum, and PsELO from Phytophthora sojae. Heterologous expression in Saccharomyces cerevisiae showed that McELO preferentially elongates C16 to C18 fatty acids, PrELO targets Δ6 polyunsaturated fatty acids, and PsELO uses long chain saturated fatty acids as substrates. McELO and PrELO exhibited more homology, potentially enabling fatty acid composition remodeling and enhanced LC-PUFAs production in oleaginous microorganisms. Site-directed mutagenesis of conserved amino acids across elongase types identified residues essential for activity, supported by molecular docking. Alanine substitution of conserved polar residues led to enzyme inactivation, underscoring their importance in the condensation reaction. Our findings offer promising elongase candidates for polyunsaturated fatty acid production, contributing to the bioindustry’s sustainable development. Full article

Phytophthora is a genus of destructive plant pathogens. Certain species are damaging to native ecosystems, forestry, and the horticultural sector, and there is evidence of their dissemination in plant imports. Horticultural nurseries are central nodes of the plant trade and previous studies have found a high diversity of Phytophthora associated with plant nursery stock. It was subsequently hypothesized that green waste disposal sites in nurseries could harbour diverse Phytophthora communities and act as a pathogen reservoir and conduit, facilitating further Phytophthora infection of nursery stock and its spread into the wider environment. This project identified Phytophthora species associated with green waste at three Scottish nurseries by sampling material from waste piles, water run-off from piles, and roots from discarded plants. Species were identified using a baiting method and sequencing of environmental DNA. Plant nursery green waste was shown to harbour diverse and varied Phytophthora species assemblages, with differences among nurseries reflecting biosecurity management practices. Eighteen Phytophthora species were detected in the samples, including the highly destructive pathogens P. ramorum and P. austrocedri. Results suggest that the improved management of waste, for example through effective on-site composting, is essential to reduce the risk of Phytophthora pathogens spreading from nurseries into the wider environment. Full article

The invasive Oomycete pathogen Phytophthora ramorum has killed millions of susceptible oak and tanoak trees in California and southern Oregon forests and is responsible for losses in revenue to the nursery industry through mitigation activities. In addition, infestation of forests in the United Kingdom by this organism has resulted in the destruction of many hectares of larch plantations. Resprouting stumps can be a reservoir for the inoculum of P. ramorum persisting on a site. In areas where the application of herbicides is not permitted, a biocontrol treatment would be an indispensable alternative. Treatment of stumps with the sap-rotting fungus Chondrostereum purpureum (Pers.) Pouzar has been shown to be an effective tool for the suppression of resprouting on several species, most notably red alder. In this project, the ability of C. purpureum to suppress resprouting was evaluated on stumps of two host species, tanoak (Notholithocarpus densiflorus) and California bay laurel (Umbellularia californica). Laboratory testing of three California isolates of C. purpureum indicated that the fungus can colonize bay laurel stems. Field trials were established near Brookings, Oregon, on tanoak and on bay laurel near Soquel, California. Early results of field testing showed that C. purpureum was able to colonize the stumps of tanoak following treatment and was found to occur naturally on tanoak logs and stumps. Formulations of C. purpureum appear to have some effect on reducing sprout survival in tanoak, but the most effective and rapid treatment for this host is the hack and squirt method of applying the herbicide imazapyr. Sprayed herbicide prevents sprouting on bay laurel, and there was evidence that resprouting was inhibited on stumps treated with C. purpureum. Over time, applications of C. purpureum may be a more permanent solution as the stumps begin to decay. Full article

Epidemiological models are important for the understanding of disease progression in plants and for the design of control strategies. Phytophthora ramorum, the pathogen responsible for the disease known as Sudden Oak Death, causes lethal infection on several oaks but relies on California bay laurels for transmission. Here, repeated surveys of bay laurels and oaks indicated that bay laurel disease incidence was positively correlated with rainfall, bay laurel density, and an eastern aspect, and negatively correlated with bay laurel basal area. Oak infection only occurred in years when rainfall was higher than the 30-year average, and although infection rates were greater among larger trees, mortality was greater among smaller trees. Additionally, larger oaks closer to infected bay laurels exhibited greater infection rates. Disease incidence differed among sites, and only a fraction of bay laurels were disease superspreaders, while even fewer individuals were refugial trees harboring active infections during dry periods. Based on this study, reducing bay laurel density in denser stands and the number of superspreaders or refugial trees in less dense stands may reduce disease incidence. However, the selective removal of bay laurel trees 0–10 m from oaks is likely to be more effective in preventing infection of specific oaks. Full article

Field surveys conducted on nine farms over a 2-year period showed the widespread presence of Phytophthora-related diseases on globe artichoke plants in the main growing area in Sardinia (Italy). Characteristic symptoms included wilting and necrosis of the outermost leaves and dark brown discoloration of stem tissues, as well as root rot. A total of 18 Phytophthora colonies belonging to three species were isolated and characterized. Based on morphological features and ITS sequence data, Phytophthora isolates were identified as P. crassamura (eight isolates) and P. cactorum (four isolates). Six isolates could not be assigned to any formally described species of Phytophthora and are therefore described here as Phytophthora marrasii sp. nov. The ITS phylogeny places P. marrasii in a terminal clade basal to the sister taxa (P. foliorum, P. hibernalis, P. lateralis, and P. ramorum) of the clade 8c. In particular, P. marrasii is phylogenetically related to P. foliorum, a species from which it differs in 62 nucleotides in the ITS region. At the same time, it can easily be distinguished morphologically from P. foliorum mainly because of the low minimum temperature for growth, the bigger and persistent non-papillate sporangia, and smaller oogonia. Pathogenicity tests confirmed that all three Phytophthora species are pathogenic on globe artichokes, which represent a new host for these pathogens. Full article

As global plant trade expands, tree disease epidemics caused by pathogen introductions are increasing. Since ca 2000, the introduced oomycete Phytophthora ramorum has caused devastating epidemics in Europe and North America, spreading as four ancient clonal lineages, each of a single mating type, suggesting different geographical origins. We surveyed laurosilva forests for P. ramorum around Fansipan mountain on the Vietnam-China border and on Shikoku and Kyushu islands, southwest Japan. The surveys yielded 71 P. ramorum isolates which we assigned to eight new lineages, IC1 to IC5 from Vietnam and NP1 to NP3 from Japan, based on differences in colony characteristics, gene x environment responses and multigene phylogeny. Molecular phylogenetic trees and networks revealed the eight Asian lineages were dispersed across the topology of the introduced European and North American lineages. The deepest node within P. ramorum, the divergence of lineages NP1 and NP2, was estimated at 0.5 to 1.6 Myr. The Asian lineages were each of a single mating type, and at some locations, lineages of “opposite” mating type were present, suggesting opportunities for inter-lineage recombination. Based on the high level of phenotypic and phylogenetic diversity in the sample populations, the coalescence results and the absence of overt host symptoms, we conclude that P. ramorum comprises many anciently divergent lineages native to the laurosilva forests between eastern Indochina and Japan. Full article

Phosphites have been used to control Sudden Oak Death; however, their precise mode of action is not fully understood. To study the mechanism of action of phosphites, we conducted an inoculation experiment on two open-pollinated tanoak families, previously found to be partially resistant. Stems of treatment group individuals were sprayed with phosphite, and seven days later, distal leaves were inoculated with the Sudden Oak Death pathogen Phytophthora ramorum. Leaves from treated and untreated control plants were harvested before and seven days after inoculation, and transcriptomes of both host and pathogen were analyzed. We found that tanoak families differed in the presence of innate resistance (resistance displayed by untreated tanoak) and in the response to phosphite treatment. A set of expressed genes associated with innate resistance was found to overlap with an expressed gene set for phosphite-induced resistance. This observation may indicate that phosphite treatment increases the resistance of susceptible host plants. In addition, genes of the pathogen involved in detoxification were upregulated in phosphite-treated plants compared to phosphite-untreated plants. In summary, our RNA-Seq analysis supports a two-fold mode of action of phosphites, including a direct toxic effect on P. ramorum and an indirect enhancement of resistance in the tanoak host. Full article

Disease outbreaks caused by introduced Phytophthora species have been increasing in British forests and woodlands in recent years. A better knowledge of the Phytophthora communities already present in the UK is of great importance when developing management and mitigation strategies for these diseases. To do this, soils were sampled in “disturbed” sites, meaning sites frequently visited by the public, with recent and new plantings or soil disturbances versus more “natural” forest and woodland sites with little disturbance or management. Phytophthora diversity was assessed using high-throughput Illumina sequencing targeting the widely accepted barcoding Internal Transcribed Spacer 1 (ITS1) region of rRNA and comparing it with the mitochondrial cytochrome c oxidase I (COI) gene. Isolation of Phytophthora was run in parallel. Nothophytophthora spp. and Phytophthora spp. were detected in 79 and 41 of the 132 locations of the 14 studied sites when using ITS or COI, respectively. A total of 20 Phytophthora amplicon sequence variants (ASVs) were assigned to known Phytophthora species from eight clades (1a, 2, 2b, 3a, 5, 6b, 7a, 8b, 8c, 8d, 10a, and 10b) and 12 ASVs from six clades (1a, 2c, 3a, 3b, 6b, 7a, 8b, 8c, and 8d) when using ITS or COI, respectively. Only at two locations were the results in agreement for ITS, COI, and isolation. Additionally, 21 and 17 unknown Phytophthora phylotypes were detected using the ITS and COI, respectively. Several Phytophthora spp. within clades 7 and 8, including very important forest pathogens such as P. austrocedri and P. ramorum, were identified and found more frequently at “disturbed” sites. Additionally, eight ASVs identified as Nothophytophthora spp. were detected representing the first report of species within this new genus in Britain. Only three species not known to be present in Britain (P. castaneae, P. capsici, and P. fallax) were detected with the ITS primers and not with COI. To confirm the presence of these or any potential new Phytophthora species, sites should be re-sampled for confirmation. Additionally, there is a need to confirm if these species are a threat to British trees and try to establish any eradication measures required to mitigate Phytophthora spread in Britain. Full article

Research Highlights: This research identified areas of the eastern United States forests that may be at particular risk from Sudden Oak Death (SOD) if it becomes established in the region. The highest suitability for SOD occurs where there are both species at risk of serious infection and species that could spread SOD to new hosts. Background and Objectives: SOD, caused by Phytophthora ramorum, can cause serious damage to forests. Although SOD is not believed to exist in the wild in the eastern United States, the presence of potential P. ramorum hosts in the area has led to questions about the potential for its establishment there. The present project expanded on previous efforts by examining both the possibility and potential consequences of P. ramorum establishment based on the presence of suitable hosts. Materials and Methods: We developed a map of the potential severity of tree loss that could result from a P. ramorum establishment in the eastern United States as well as a habitat suitability index based on the density of P. ramorum susceptible and spreader host species. We also implemented a connectivity analysis method for determining patches important to the spread of P. ramorum in the Great Smoky Mountains National Park. Results: The Ozarks and Appalachians both had a high potential severity of infection due to their high percentage of susceptible species, but the Appalachians had a higher overall level of risk due to the presence of more spreader tree species in the area. Connectivity analysis in the Great Smoky Mountains National Park identified patches likely to be particularly important to P. ramorum spread. Conclusions: Analysis of the presence of potential P. ramorum hosts in the eastern United States identified suitable conditions for SOD establishment there, particularly in the Appalachians. Techniques developed in this research can identify critical areas for SOD spread at both landscape and regional scales. Full article