Prevalence of Phytophthora species in macadamia orchards in Australia and their ability to cause stem canker

In Australia, Phytophthora cinnamomi is the only species reported as the causal agent of stem canker and root rot in macadamia. In other countries, five Phytophthora species have been reported to cause diseases in macadamia, which led us to question if more than one Phytophthora species is responsible for poor tree health in macadamia orchards in Australia. To investigate this, samples were collected from the rhizosphere, stem, and root tissues of trees with and without symptoms, nurseries, and water sources from 70 commercial macadamia orchards in Australia. Phytophthora isolates were identified based on morphological characteristics and DNA sequencing. P. cinnamomi was the most predominant and widely distributed species, and was obtained from the different types of samples including symptomless root tissues. In addition to P. cinnamomi, only P. multivora was isolated from diseased tissue (stem canker) samples. Six other Phytophthora species were obtained from the rhizosphere samples: P. pseudocryptogea, P. citrophthora, P. nicotianae, P. gondwanense, P. sojae, and a new Phytophthora taxon. Only P. cinnamomi was obtained from macadamia nursery samples, while five Phytophthora species were obtained from water sources. Of the heterothallic Phytophthora species, mating type A2 isolates were dominant in P. cinnamomi isolates, whereas only mating type A1 isolates were obtained for P. nicotianae, P. pseudocryptogea, and P. citrophthora. Pathogenicity assays revealed that P. cinnamomi and P. multivora caused significantly larger stem and leaf lesions than P. citrophthora, P. nicotianae, and P. pseudocryptogea. Phytophthora sp. and P. sojae were nonpathogenic towards leaves and stems.     

Characterisation and detection of Pythium and Phytophthora species associated with grapevines in South Africa

Replant and decline diseases of grapevines not only cause quantitative and qualitative yield losses, but also result in extra costs when vineyards have to be replanted. This study investigated the role of Pythium and Phytophthora in the decline syndrome in South Africa by determining (1) the species associated with nursery and established vines, and (2) pathogenicity of Ph. sp. niederhauserii and P. vexans relative to known grapevine pathogens. Quantitative real-time PCR (qPCR) assays were also developed for detection of the most prevalent oomycete groups. In total, 26 Pythium and three Phytophthora species were identified from grapevine nurseries and established vineyards. The most common infections in sampled nursery vines were caused by P. vexans (16.7%), followed by P. ultimum var. ultimum (15.0%) and P. irregulare (11.7%). In established vineyards, P. irregulare (18.0%) and P. vexans (6.2%) were also among the three most prevalent species, along with P. heterothallicum (7.3%). Three Phytophthora species were also identified from the sampled established vines, of which Ph. cinnamomi (5.1%) was predominant, followed by Ph. sp. niederhauserii (1.1%). In established vineyards a higher incidence and more diverse species composition was observed in spring and winter, than in summer. Pathogenicity studies showed that some Ph. sp. niederhauserii and P. vexans isolates were as aggressive as the known grapevine pathogens Ph. cinnamomi and P. irregulare. Sensitive qPCR assays were developed for the detection of P. ultimum var. ultimum, P. irregulare, P. vexans and the genus Phytophthora. These assays will be invaluable in limiting pathogen dispersal through screening of nursery material. This is especially important since pathogenic species were also isolated from healthy looking vines in nurseries.     

Phytophthora lateralis discovered in an old growth Chamaecyparis forest in Taiwan

The geographic origins of the invasive Phytophthora species, P. lateralis and P. ramorum are unknown. In 2008 soil samples were collected in an old growth yellow cedar (Chamaecyparis obtusa var. formosana) stand in the Ma‐kau Ecological Park in north eastern Taiwan and subjected to Phytophthora baiting procedures at 18°C. Cedar needle baits yielded isolates of a slow growing Phytophthora culture from one soil sample, together with P. cinnamomi. Phytophthora bisheria sp. nov. was obtained from another sample. The slow growing isolates conformed closely to P. lateralis in the morphology of their sporangia and chlamydospores, growth–temperature relationships, absence of gametangia and their ITS and cox II sequences. The isolates’ sporangia were partially caducous, with short pre‐formed pedicels of ca. 3–5 μm, a highly unusual feature in a non‐papillate Phytophthora. The isolates also produced multicellular stromata on cedar decoction agar. Small morphological and molecular differences were observed between the Taiwan‐isolates and Oregon‐control isolates. Taiwan may lie within the geographic centre of origin of P. lateralis. By analogy Japan may also lie within the natural range of P. lateralis; and Japan, along with Taiwan and Yunnan, could be an origin for the closely related P. ramorum.     

Pathogenicity of 21 newly described Phytophthora species against seven Western Australian native plant species

The pathogenicity of some Phytophthora species recently described from Western Australia, together with P. cinnamomi as a control, was tested against seven Western Australian native plant species in the glasshouse. Host species were Banksia grandis, B. littoralis, B. occidentalis, Casuarina obesa, Corymbia calophylla, Eucalyptus marginata and Lambertia inermis. Twenty‐two Phytophthora species were grown on a vermiculite, millet seed and V8 substrate and used as soil inoculum when the plant hosts were approximately 3 months old. Pathogenicity was assessed after 6 weeks and plants were scored for death, root damage, and percentage reduction of shoot growth compared with control plants. The pathogenicity of P. cinnamomi was confirmed. Phytophthora niederhauserii was shown to be similar to P. cinnamomi in pathogenicity and of concern ecologically. Other species that killed one or more hosts were P. boodjera, P. constricta, P. elongata, P. moyootj and P. rosacearum, while P. condilina, P. gibbosa, P. gregata, P. litoralis and P. ‘personii’ caused significant reduction to shoot and/or root growth, but did not kill plants. Host species susceptible to the highest number of Phytophthora species were B. grandis, B. littoralis, B. occidentalis and E. marginata. No Phytophthora species tested killed C. calophylla.     

Age‐related susceptibility of Eucalyptus species to Phytophthora boodjera

Phytophthora boodjera is a newly described pathogen causing damping off and mortality of Eucalyptus seedlings in Western Australian nurseries. This study evaluated the age‐related susceptibility of several taxa of mallee Eucalyptus to P. boodjera in sterilized washed river sand‐infestation pot trials. Phytophthora cinnamomi and P. arenaria were included for comparison. Seedlings of Eucalyptus taxa were inoculated at 0, 2, 4, 12 and 88 weeks with individual Phytophthora isolates. Pre‐emergent mortality in the presence of Phytophthora was almost 100%. Post‐emergent mortality was 50–100%, depending on isolate, compared to 0% for the control. Mortality was also high for inoculated 1 month‐old seedlings (46–68%) and root length of surviving seedlings was severely reduced. Death from root infection was not observed for seedlings inoculated at 12 and 88 weeks, but they developed root necrosis and reduced root dry weight compared to non‐inoculated controls. Phytophthora boodjera is a pre‐ and post‐emergent pathogen of mallee eucalypts. These eucalypts are susceptible to P. boodjera at all life stages tested, but the mortality rates declined with plant age. Similar results were obtained for P. cinnamomi and P. arenaria. The events leading to its recent appearance in the nurseries remain unknown and further investigations are underway to determine if this is an introduced or endemic pathogen. The approach used here to understand the impact of a Phytophthora species on multiple hosts at different seedling ages is novel and sets a benchmark for future work.     

Phytophthora diversity and the population structure of Phytophthora ramorum in Swiss ornamental nurseries

Invasive oomycete pathogens have been causing significant damage to native ecosystems worldwide for over a century. A recent well‐known example is Phytophthora ramorum, the causal agent of sudden oak death, which emerged in the 1990s in Europe and North America. In Europe, this pathogen is mainly restricted to woody ornamentals in nurseries and public greens, while severe outbreaks in the wild have only been reported in the UK. This study presents the results of the P. ramorum survey conducted in Swiss nurseries between 2003 and 2011. In all 120 nurseries subjected to the plant passport system, the main P. ramorum hosts were visually checked for above ground infections. Phytophthora species were isolated from tissue showing symptoms and identified on the basis of the morphological features of the cultures and sequencing of the ribosomal ITS region. Phytophthora was detected on 125 plants (66 Viburnum, 58 Rhododendron and one Pieris). Phytophthora ramorum was the most frequent species (59·2% of the plants), followed by P. plurivora, P. cactorum, P. citrophthora, P. cinnamomi, P. cactorum/P. hedraiandra, P. multivora and P. taxon PgChlamydo. The highest incidence of P. ramorum was observed on Viburnum × bodnantense. Microsatellite genotyping showed that the Swiss P. ramorum population is highly clonal and consists of seven genotypes (five previously reported in Europe, two new), all belonging to the European EU1 clonal lineage. It can therefore be assumed that P. ramorum entered Switzerland through nursery trade. Despite sanitation measures, repeated P. ramorum infections have been recorded in seven nurseries, suggesting either reintroduction or unsuccessful eradication efforts.     

Zoospore chemotaxis of closely related legume‐root infecting Phytophthora species towards host isoflavones

Phytophthora niederhauserii, P. pisi, P. sojae and P. vignae are closely related species that are pathogenic to various legume plants. While P. sojae and P. vignae are reported to specifically infect soybean and cowpea, respectively, P. pisi is reported to attack pea and faba bean. Phytophthora niederhauserii is considered to have a broad host range. Zoospores of some Phytophthora species are chemotactically attracted to the isoflavones that are secreted by their host plants. The focus of the current study was to determine the chemotaxic behaviour of zoospores from closely related legume‐root infecting Phytophthora species and to investigate the correlation, if any, to host preference as determined by greenhouse pathogenicity tests. The results showed that P. sojae and P. vignae were attracted to the non‐soybean isoflavone prunetin as well as to the soybean isoflavones genistein and daidzein, which is in contrast with their host specificity on soybean and cowpea, respectively. On the other hand, P. pisi and P. niederhauserii were only attracted to prunetin, previously reported to be produced by pea, but not to the isoflavones associated with the non‐host soybean. The lack of responsiveness to genistein and daidzein in P. pisi may represent a recent adaptation to the host specialization towards pea. However, the affinity of P. niederhauserii to prunetin shows that this trait can also be present in taxa not specifically associated with legume hosts.     

Molecular and Pathogenicity Characteristics of Phytophthora nicotianae Responsible for Root Necrosis and Wilting of Pepper (Capsicum annuum L.) in Tunisia

Isolates of Phytophthora from pepper, produced in Tunisia, were characterised according to molecular and pathogenicity criteria. Polymerase chain reaction amplification of the ITS1 region in the ribosomal DNA resulted in different sized fragments. The pepper isolates and P. nicotianae yielded a fragment of 310bp that distinguished it from P. capsici with a fragment of 270bp. The ribosomal RNA gene amplicons of both internal transcribed spacers and the 5.8 S of the pepper Phytophthora and P. nicotianae were digested with 8 endonucleases. The patterns generated, with the 2 enzymes that cut, were identical for both taxa. This molecular analysis corroborated the morphological and biological characteristics and suggests strongly that the isolates of Phytophthora from pepper belong to the species P. nicotianae. Inoculation of pepper, tomato, eggplant and tobacco plants with the isolates of P. nicotianae from pepper showed they were highly pathogenic on pepper but not on tobacco, while their pathogenicity was weak on tomato and eggplant and was associated with atypical symptoms not observed in the field. These pathogenicity tests suggest that pepper isolates of P. nicotianae are particularly adapted to their host and may thus constitute a forma specialis of P. nicotianae.     

Metabarcoding and development of new real‐time specific assays reveal Phytophthora species diversity in holm oak forests in eastern Spain

The evergreen holm oaks (Quercus ilex subsp. ilex and Q. ilex subsp. ballota) are the most representative tree species in the Iberian peninsula and the main tree species in oak‐rangeland ecosystems (dehesas). Oak decline in western, central and southern parts of Spain has been associated with root rot caused by Phytophthora cinnamomi for decades. However, Phytophthora species such as P.  quercina and P. psychrophila have recently been found associated with Quercus decline in eastern Spain where calcareous soils are predominant. Soil and root samples from two Quercus forests presenting decline symptoms in two different geographical areas in eastern Spain (Carrascar de la Font Roja and Vallivana) were analysed by amplicon pyrosequencing. Metabarcoding analysis showed Phytophthora species diversity, and revealed that an uncultured Phytophthora taxon, named provisionally Phytophthora taxon ballota, was the predominant species in both areas. In addition, a real‐time PCR assay, based on the pyrosequencing results, was developed for the detection of this uncultured Phytophthora taxon, and also for the detection of P. quercina. TaqMan assays were tested on soil and root samples, and on Phytophthora pure cultures. The new assays showed high specificity and were consistent with metabarcoding results. A new real‐time PCR protocol is proposed to evaluate the implication of different Phytophthora spp. in oak decline in eastern Spain.     

Diversity of Phytophthora species in natural ecosystems of Taiwan and association with disease symptoms

In 2013 a survey of Phytophthora diversity was performed in 25 natural and seminatural forest stands and 25 rivers in temperate montane and subtropical lowland regions of Taiwan. Using baiting assays, 10 described species and 17 previously unknown taxa of Phytophthora were isolated from 71.5% of the 144 rhizosphere soil samples from 33 of 40 tree species sampled in 24 forest stands, and from 19 rivers: P. capensis, P. citrophthora, P. plurivora, P. tropicalis, P. citricola VII, P. sp. × botryosa‐like, P. sp. × meadii‐like and P. sp. occultans‐like from Clade 2; P. palmivora from Clade 4; P. castaneae and P. heveae from Clade 5; P. chlamydospora and P. sp. forestsoil‐like from Clade 6; P. cinnamomi (Pc), P. parvispora, P. attenuata nom. prov., P. flexuosa nom. prov., P. formosa nom. prov., P. intricata nom. prov., P. × incrassata nom. prov. and P. × heterohybrida nom. prov. from Clade 7; P. sp. palustris and five new hybrid species from Clade 9. The A1 mating type of Pc was widespread in both montane and lowland forests and rarely associated with disease, whereas the A2 mating type was limited to lowland forests and in some cases causing severe dieback. Most other Phytophthora species were not associated with obvious disease symptoms. It is concluded that (i) Taiwan is within the centre of origin of most Phytophthora taxa found, (ii) Pc A2 is an introduced invasive pathogen, and (iii) interspecific hybridizations play a major role in speciation and species radiations in diverse natural ecosystems.     

Specific and Sensitive Detection of Phytophthora nicotianae By Simple and Nested-PCR

Phytophthora nicotianae Breda de Haan is one of the most important soil-borne plant pathogens. The identification of this pathogen based on morphological or physiological characters is time-consuming and labour-intensive and requires comprehensive knowledge of fungi. Molecular analysis of the internal transcribed spacer (ITS) regions of rDNA is a novel and very effective method of species determination. Based on this concept, conventional and single closed tube nested-PCRs were developed for the specific and sensitive detection of P. nicotianae. Two new specific primers, designed from the spacer regions ITS1 and ITS2, internal to the nucleotide sequence flanked by universal primers ITS4 and ITS6, were used. To evaluate the specificity of the method, 36 morphologically characterized isolates were tested. A positive reaction, characterized by an amplification product of 737 bp, was shown by all P. nicotianae isolates and two P. nicotianae/cactorum hybrids. No amplification product was observed when other Phytophthora species and genera were assayed. The sensitivity of this method was analysed by serial dilutions of a defined amount of fungal DNA in a healthy root extract. Nested-PCR was at least 1000 times more sensitive than conventional PCR. In addition, samples from different infection sites, origins and crops, samples from nutrient solution, water and the rockwool used in hydroponic cultures, were analysed to validate this method.     

Diversity and detections of Phytophthora species from trade and non‐trade environments in Ireland

The genus Phytophthora is one of the genera of organisms that poses the most threat to plant health worldwide. Statutory monitoring for Phytophthora species focuses on the species regulated in the European Union and recommended for regulation by EPPO (Plant Health Directive 2000/29 EC and the EPPO A2 List). This research provides details of the Phytophthora species detected from trade and non‐trade environments in Ireland between 2013 and 2015. The results of statutory surveys for the regulated species Phytophthora ramorum, Phytophthora kernoviae and Phytophthora lateralis from 2003 to 2015 are also presented. Testing of more than 11 000 samples was carried out using morphological and/or DNA identification with specifically designed Phytophthora conserved primers. This led to the detection of 19 species and 3 informally designated taxa of Phytophthora, including 8 new records for Ireland. Eight species were found in both trade and non‐trade locations, and three informally designated taxa were also detected. Phytophthora ramorum was found on the most hosts (30 hosts), followed by Phytophthora syringae (6 hosts) and Phytophthora kernoviae (3 hosts). Rhododendron was the host on which Phytophthora species were most frequently detected (12 Phytophthora species). The role of the plant trade in spreading invasive Phytophthora species is discussed.     

Detection of <Emphasis Type="Italic">Phytophthora nicotianae</Emphasis> and <Emphasis Type="Italic">P. palmivora</Emphasis> in citrus roots using PCR-RFLP in comparison with other methods

Phytophthora nicotianae and P. palmivora are the most important soil-borne pathogens of citrus in Florida. These two species were detected and identified in singly and doubly infected plants using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) of internal transcribed spacer (ITS) regions of ribosomal DNA. The sensitivity of the PCR-RFLP was analyzed and the usefulness of the method evaluated as an alternative or supplement to serological methods and recovery on semi-selective medium. In a semi-nested PCR with universal primers ITS4 and ITS6, the detection limit was 1 fg of fungal DNA, which made it 1000× more sensitive than a single-step PCR with primers ITS4 and DC6. The sensitivity of detection for P. nicotianae was shown to be ten-fold lower than for P. palmivora, limiting its detection with restriction profiles in plants infected by both fungal species. Phytophthora nicotianae was detected with species-specific primers in all samples inoculated with this species despite the absence of species-specific patterns in RFLP. In contrast, the incidence of detection of P. palmivora in the presence of P. nicotianae was considerably lower using plating and morphological detection methods. Due to its high sensitivity, PCR amplification of ribosomal ITS regions is a valuable tool for detecting and identifying Phytophthora spp. in citrus roots, provided a thorough knowledge of reaction conditions for the target species is established prior to the interpretation of data.     

Towards a best practice methodology for the detection of Phytophthora species in soils

The genus Phytophthora contains species that are major pathogens worldwide, affecting a multitude of plant species across agriculture, horticulture, forestry, and natural ecosystems. Here, we concentrate on those species that are dispersed through soil and water, attacking the roots of the plants, causing them to rot and die. The intention of this study was to compare the soil baiting protocol developed by the Centre for Phytophthora Science and Management (CPSM) with two other baiting methods used in Australia. The aim was to demonstrate the effectiveness of each protocol for soil baiting Phytophthora species in different substrates. Three experiments were conducted: the first to test the sensitivity of each method to detect Phytophthora cinnamomi, the second to test the effect of substrate type (sand or loam), and the third to test the detection of species (P. cinnamomi, P. multivora, or P. pseudocryptogea). The specificity of different plant species baits was compared within and between the methods. Substrate type influenced isolation in all methods; however, the CPSM method was superior regardless of substrate, albeit slower than one of the other methods for one substrate. Comparing bait species between the three methods, Quercus ilex was the most attractive bait for P. cinnamomi, particularly in the CPSM method. The choice of protocol affected the isolation associated with each bait type. Overall, the multiple bait system used by CPSM was shown to provide the most sensitive and reliable detection of Phytophthora species from soil samples.     

Potential of Ypt1 and ITS gene regions for the detection of Phytophthora species in a lab‐on‐a‐chip DNA hybridization array

A novel DNA‐chip hybridization assay that uses the ras‐related GTP‐binding protein 1 gene (Ypt1) was developed for the identification of several devastating Phytophthora species. The hybridization was conducted in a portable microfluidic lab‐on‐a‐chip device for fast and accurate detection of 40 Phytophthora, two Pythium and one Phytopythium species. Moreover, the functionality of the Ypt1 region was examined in comparison to an array for the internal transcribed spacer (ITS) region by in silico modelling. The difference in species‐specific capture probe sequences was lower for the ITS than for the Ypt1 region. While ITS‐probes of Phytophthora ramorum, Phytophthora fragariae and Phytophthora lateralis cross‐reacted with up to 11 non‐target species, Ypt1‐probes were specific except for P. fragariae/Phytophthora rubi. First analyses of artificially inoculated Rhododendron leaves successfully demonstrated the usability of the respective capture probes for the Ypt1 and the ras‐related plant protein Rab1a gene region. The on‐chip hybridization enabled the detection of up to 1 pg μL^?1 target DNA depending on the species examined. Due to the complementarity of ITS and Ypt1 genetic features, the use of multiple loci is recommended to identify targets of different taxonomic rank.     

Detection of Phytophthora nicotianae and P. citrophthora in Citrus Roots and Soils by Nested PCR

The polymerase chain reaction (PCR) was used for the specific detection of Phytophthora nicotianae and P. citrophthora in citrus roots and soils. Primers were based on the nucleotide sequences of the internal transcribed space regions (ITS1 and ITS2) of 16 different species of Phytophthora. Two primer pairs, Pn5B–Pn6 and Pc2B–Pc7, were designed specifically to amplify DNA from P. nicotianae and P. citrophthora, respectively. Another primer pair (Ph2–ITS4) was designed to amplify DNA from many Phytophthora species. All primer pairs were assessed for specificity and absence of cross-reactivity, using DNA from 118 isolates of Phytophthora and 82 of other common soil fungi. In conventional PCR, with a 10-fold dilution series of template DNA, the limit of detection was of 1pgl^–1 DNA for all the primer pairs (Ph2–ITS4, Pn5B–Pn6, and Pc2B–Pc7). In nested PCR, with primers Ph2–ITS4 in the first round, the detection limit was of 1fgl^–1 for both the primer sets (Pn5B–Pn6 and Pc2B–Pc7). Simple, inexpensive and rapid procedures for direct extraction of DNA from soil and roots were developed. The method yielded DNA of a purity and quality suitable for PCR within 2–3h. DNA extracted from soil and roots was amplified by nested PCR utilizing primers Ph2–ITS4 in the first round. In the second round the primer pairs Pn5B–Pn6 and Pc2B–Pc7 were utilized to detect P. nicotianae and P. citrophthora, respectively. Comparison between the molecular method and pathogen isolation by means of a selective medium did not show any significant differences in sensitivity.     

Phytophthora acerina sp. nov., a new species causing bleeding cankers and dieback of Acer pseudoplatanus trees in planted forests in northern Italy

A severe dieback of Acer pseudoplatanus trees was noticed in planted forest stands in northern Italy in 2010. Affected trees showed collar rot and aerial bleeding cankers along the stems, leading to crown dieback and eventually death. An unknown Phytophthora species was consistently isolated from necrotic bark and xylem tissue and from rhizosphere soil. Based on its unique combination of morphological and physiological characters and phylogenetic analysis, this new taxon is here described as Phytophthora acerina sp. nov. Phylogenetic analysis of ITS, cox1 and β‐tubulin gene regions demonstrated that P. acerina is unique and forms a separate cluster within the ‘P. citricola complex’, closely related to P. plurivora. Phytophthora acerina is homothallic with smooth‐walled oogonia, thick‐walled, mostly aplerotic oospores with a high abortion rate, paragynous antheridia, and persistent, morphologically variable semipapillate sporangia. Four to 5‐week‐old cultures produced globose to subglobose, appressoria‐like and coralloid hyphal swellings and characteristic stromata‐like hyphal aggregations. Optimum and maximum temperatures for growth are 25°C and 32°C, respectively. Genetic uniformity of all 15 studied isolates and the apparent absence of this species in the extensive surveys of nurseries, forests and seminatural ecosystems conducted in the previous two decades across Europe indicate a recent clonal introduction to northern Italy. Under‐bark inoculation tests demonstrated high aggressiveness of P. acerina to A. pseudoplatanus indicating that this pathogen might be a serious risk to maple plantations and forests in Europe.     

Phosphorous acid treatments control Phytophthora diseases in Australia1

Treatments with a partially neutralized formulation of phosphorous acid containing potassium phosphite were assessed for control of Phytophthora diseases in subtropical and temperate crops in Australia. In Queensland, trunk injections of phosphite (10% solution) controlled severe root rot (Phytophthora cinnamomi) of avocado trees and resulted in the recovery of trees. Single pre-harvest sprays (2.5 kg ha^-1) of phosphite controlled root and heart rot (P. cinnamomi) of pineapples. Foliar sprays of phosphite (64 g per tree) controlled root rot (P. nicotianae var. parasitica) and trunk canker (P. citrophthora) of mandarin trees. In Victoria, a foliar spray of phosphite (300 g ha^-1) reduced root rot (P. clandestina) of subterranean clover and increased dry matter by 1.96 to 5.11 t ha^-1. Trunk injections of phosphite (10% solution) controlled trunk rot (P. cactorum) of peach trees and foliar sprays (10 kg ha^-1) reduced severity of root rot (P. nicotianae var. nicotianae) of tomatoes.     

Occurrence and distribution of <Emphasis Type="Italic">Phytophthora</Emphasis> species in European chestnut stands,and their association with Ink Disease and crown decline

The Phytophthora complex associated with Castanea sativa Mill. was investigated in five European countries in 35 regions and with respect to various domestication levels. Annual precipitation and length of drought season were the main parameters that regulated the presence of Phytophthora species in the chestnut stands. Seven species of Phytophthora were detected; three of these, P. megasperma, P. cryptogea and P. syringae had not been previously reported on sweet chestnut. P. cinnamomi. P. cambivora and P. citricola were most frequently isolated. P. cinnamomi and P. cambivora were the species significantly associated with declining trees with symptoms of Ink Disease. P. cinnamomirequired distinct ecological conditions compared to the other species. P. cinnamomi was never detected in sites characterized by minimum temperatures below 1.4 °C, maximum temperature above 28 °C, or soil pH below 5.4. The results obtained provide useful information for modeling the probability of Ink Disease, crown decline and associated Phytophthora species in chestnut groves in global climatic change scenarios.     

Observations of Phytophthora spp. in Water Recirculation Systems in Commercial Hardy Ornamental Nursery Stock

Samples of water and sediment were taken from drains, reservoirs and wells from four commercial hardy ornamental nurseries with water recirculation systems. The samples were taken on seven different dates throughout a single year from August 1994 to July 1995. The samples were screened for Phytophthora species using five different methods: direct plating, three bait tests (using lupin seedlings, apples and Rhododendron leaves) and a DAS-ELISA (double-antibody sandwich enzyme-linked immunosorbent-assay) with two antisera. In the nurseries with old water recirculation systems, Phytophthora species were detected in the drains and in the reservoirs. In the nursery with a new recirculation system, the pathogens were only present in the drains. None of the water samples from wells in any of the nurseries were contaminated. Phytophthora species were present in the water as well as in the sediment samples from drains and reservoirs. They were detected in the water recirculation systems irrespective of the season. The number of isolates increased about sevenfold between late summer and spring. At least 12 different Phytophthora species were identified: some isolates were previously unrecorded species. The epidemiology of the pathogens in outdoor water recirculation systems as well as the importance of the results for commercial nurseries is discussed.