Phytophthora species in oak ecosystems in Turkey and their association with declining oak trees

From 1999 to 2001, a survey on the occurrence of Phytophthora spp. in the rhizosphere soil of healthy and declining oak trees was conducted in 51 oak stands in Turkey. Seven Phytophthora spp. were recovered from six out of the nine oak species sampled: P .  cinnamomi , P .  citricola , P .  cryptogea , P .  gonapodyides , P .  quercina , Phytophthora sp. 1 and Phytophthora sp. 2. The most frequently isolated species, P .  quercina , was very common on slopes susceptible to drought. It occurred in four different climatic zones and on six Quercus spp., suggesting that it is native to oaks. The second most common species, P .  citricola , was separated into three subgroups: type C was recovered only in Anatolia, whereas A and B occurred only in the European part of Turkey. Phytophthora cinnamomi was recovered at one site only, and may not be involved in oak decline in Turkey. The other four species were recovered sporadically. On affected sites there was a significant association between deteriorating crown status and the presence of Phytophthora spp., particularly P .  quercina . The occurrence of Phytophthora species was significantly influenced by soil pH. Stem inoculation tests on oak seedlings revealed that Q .  petraea was the most susceptible species.     

Interaction between root rot basidiomycetes and Phytophthora species on pedunculate oak

Forest declines are usually complex multifactorial phenomena that involve interactions between different factors. The possible interaction between different types of mycelial pathogens was investigated through artificial inoculation of oak seedlings, involving two root rot basidiomycetes, Collybia fusipes and Armillaria mellea, and two Phytophthora species, P. cinnamomi and P. cambivora. These pathogens were inoculated onto young Quercus robur saplings in greenhouse conditions, either alone or combining a root rot basidiomycete with a Phytophthora species. Three out of the four Phytophthora spp.*root rot basidiomycete combinations tested resulted in significantly greater damage to the oak host than the sum of the damages induced by the individual pathogens. This positive interaction could be significant in oak decline syndrome.     

Root infection by Phytophthora cinnamomi in seedlings of three oak species

The combination of soil infestation with Phytophthora cinnamomi and repetitive flooding was studied on 1-year-old plants of Quercus ilex (holm oak) and Q. suber (cork oak). In a second experiment, using 2-year-old plants of the same species and of red oak ( Q. rubra ), the soil infestation was followed by two drought-rewatering cycles. Oak predawn leaf water potential (PLWP) and stomatal conductance (gs) were monitored during both experiments. Root infection, root loss, wilting and mortality were assessed at the end of the experiments. Q. ilex exhibited the highest susceptibility to P. cinnamomi , and Q. rubra the lowest. Root infections caused by P. cinnamomi were more severe in the flooding than in the drought experiment. The most noticeable effect of the infection on plant water relations was a decrease in stomatal conductance. This occurred at different times after inoculation, varying with species susceptibility and experiment. Inoculation with P. cinnamomi induced a decrease of PLWP in Q. ilex plants, and in some Q. suber plants exhibiting a severe root loss. The results further showed that the relationship between PLWP and gs was modified by infection with P. cinnamomi . The combination of flooding and infection with P. cinnamomi acted synergistically on the water relations of Q. ilex . By contrast, there was no significant increase in disease severity due to the postinoculation water stress imposed on the oaks.     

Relationships between health of Quercus robur, occurrence of Phytophthora species and site conditions in southern Sweden

The effect of Phytophthora species, soil chemistry, precipitation and temperature on the vitality of oak was evaluated in 32 oak stands in southern Sweden. In addition, the relationship between the occurrence of Phytophthora species and soil conditions was determined. The results showed that there was a weak association between the presence of P. quercina , the most frequently recovered Phytophthora species in southern Sweden, and the vitality of the oak stands (determined from estimates of crown defoliation of individual trees). The pathogens occurred more frequently in clayey and loamy soils that were less acidic and which had higher base saturation. However, they were found in all but the most acidic soils (pH < 3·5). In stands where Phytophthora species were not present, positive correlations between the average crown defoliation and proportion of damaged trees with average summer precipitation and average annual precipitation were found. There were no significant differences in soil chemistry between healthy and declining stands included in this study, and no significant correlations were found between any soil parameter and crown vitality. Based on the results from these 32 oak stands, it is likely that the decline of oaks in southern Sweden can be attributed to several different site-specific factors, such as infection by P. quercina or unusual weather events, which interact with a number of biotic and abiotic factors, leading to oak decline.     

Comparative aggressiveness of standard and variant hybrid alder phytophthoras, Phytophthora cambivora and other Phytophthora species on bark of Alnus, Quercus and other woody hosts

Pathogenicity tests were carried out on the bark of Alnus glutinosa with 19 isolates of the standard (near-tetraploid) hybrid alder phytophthora, nine isolates representing its known heteroploid variants and 11 isolates of P. cambivora , a probable parent species of the hybrid. Over a 4-year period, 12 experiments were conducted on living alder logs incubated at 20°C. Most isolates of the standard hybrid and those of the 'Dutch variant' were highly aggressive to alder bark. Isolates of the 'Swedish', 'UK' and 'German variants', and of P. cambivora , were only weakly pathogenic. Also, isolates of P. fragariae , P. cinnamomi , P . sp. 'O-group', P. cryptogea , P. megasperma , P. gonapodyides and P. citricola were either weakly or nonpathogenic. Rates of lesion development were greatest on logs cut during July–October, slower on logs cut between November and March and zero on logs cut during April, indicating a strong seasonal effect. Other evidence indicated that lesion development was subject to critical thresholds of host resistance. The standard hybrid was nonpathogenic to the bark of four other hardwood and two conifer species, indicating that it is relatively host specific. In contrast, P. cambivora was an aggressive pathogen on live bark of Quercus and Castanea . The significance of these results is discussed.     

接种体密度、土壤水分基质势和土壤温度对辣椒疫病死苗率的影响

 在生长箱内控制条件下分析测定了接种体密度、土壤水分基质势和土壤温度对辣椒疫病死苗率的影响。结果表明,在每克干土中接种1个辣椒疫霉菌孢子囊就能造成侵染,引致辣椒死苗,随着接种体密度升高死苗率增大,直至接种体孢子囊密度达到50~80个/g干土时死苗率达到最高。土壤温度和土壤水分状况是决定辣椒疫病死苗率的重要因子,病菌侵染的最适土温是22~28℃,土壤水分接近饱和,即土壤水分基质势(Ψ_m值)为0时最容易侵染发病,土壤过于干燥和过饱和都不利于侵染发病。辣椒疫病死苗率与土壤温度、土壤水分基质势及其互作之间可用数学模式描述。     

Involvement of Iron and Ferritin in the Potato–Phytophthora infestans Interaction

This work shows that the infection of potato (Solanum tuberosum) detached leaves by the late blight pathogen Phytophthora infestans, was drastically reduced by adding deferoxamine, an exogenous iron chelator. Reactive oxygen species in leaves inoculated with P. infestans were also reduced after adding deferoxamine. A leaf ferritin cDNA fragment was obtained by PCR and used as probe for screening a tuber cDNA library. A cDNA (named StF1) encoding the iron-storing potato ferritin was cloned. StF1 is 915 bp in length and has an open reading frame of 230 amino acids that contains the information for the mature 28 kDa subunit of potato ferritin. StF1 was used as probe in northern blot hybridizations to analyze expression of the ferritin gene. In leaves, ferritin mRNA accumulated in response to pathogen attack. In tubers, ferritin mRNA increased upon treatment with the elicitor eicosapentaenoic acid. These results suggest that iron plays a role in the potato-P. infestans interaction.     

库布齐沙地柠条根际土壤微生物生物量及其与土壤因子的关系

对库布齐沙地柠条根际、非根际土壤微生物生物量碳、氮分布状况及其与土壤因子的关系进行了研究。结果表明:柠条土壤生物量碳、氮含量的分布趋势均为根际土壤>非根际土壤>流沙,且以表层(0-10cm)最高,随土层加深,呈下降趋势;柠条土壤中微生物量碳、氮对土壤有机质、全氮的贡献率分别为1.55%-4.73%,5.61%-13.39%,微生物量碳氮比为3.10-7.22;微生物量碳氮间呈显著正相关,土壤全氮、有机质含量与土壤微生物生物量碳、氮相关性最大。     

辣椒疫病发病主导因素及综合防治技术研究

通过3a在多年辣椒重茬地的田间试验及调查研究,基本明确了辣椒疫病发生与灌水方法、栽培方式、降水、中心病株的出现等主导因素的关系。提出了栽培防病、化学治疗的综防技术,达到控病增产的目的。     

Effect of host factors on the susceptibility of Rhododendron to Phytophthora ramorum

Phytophthora ramorum causes sudden oak death (SOD) in western coastal forests of the USA. In Europe, the pathogen is mainly present in the nursery industry, particularly on Rhododendron. Because of the primary role of Rhododendron as a host and potentially as a vector, the effect of Rhododendron host factors on P. ramorum susceptibility and sporulation was investigated. Inoculation methods using either wounded or non‐wounded detached leaves were applied to 59 Rhododendron cultivars and 22 botanical species, replicated in three separate years. All Rhododendron species and cultivars were susceptible when using wounded leaves, but not when using non‐wounded leaves, suggesting a resistance mechanism operating at the level of leaf penetration. Using a regression tree analysis, the cultivars and species were split into four susceptibility classes. Young leaves were more susceptible than mature leaves when wounded, but less susceptible when non‐wounded. This effect was not correlated with leaf hydrophobicity or the number of leaf hairs. The presence or the type of rootstock did not affect the cultivar susceptibility level. Sporangia and chlamydospore production in the leaf lesions varied widely among Rhododendron cultivars and was not correlated with the susceptibility level. The susceptibility to P. ramorum correlated well with the susceptibility to P. citricola and P. hedraiandra × cactorum, suggesting that the resistance mechanisms against these species are non‐specific. Susceptibility to P. kernoviae was low for most cultivars. These findings have implications for detection, spread and disease control, and are therefore important in pest risk assessment.     

Two novel and potentially endemic species of Phytophthora associated with episodic dieback of Kwongan vegetation in the south‐west of Western Australia

Two novel homothallic species of Phytophthora causing dieback of Kwongan vegetation in south‐west Western Australia are described here as Phytophthora arenaria sp. nov. and Phytophthora constricta sp. nov. DNA sequencing of the ITS rDNA and cox1 gene confirmed that P. arenaria and P. constricta are unique species residing in ITS clades 4 and 9, respectively. Phytophthora arenaria has been isolated from vegetation occurring on the northern sandplains which are warmer and drier than the southern sandplains from which P. constricta has been predominantly isolated, and both species appear morphologically and physiologically well adapted to the ecosystems in which they occur. Both species have been associated mainly with dead and dying Banksia species and the pathogenicity of both P. arenaria and P. constricta to Banksia attenuata was confirmed in this study. The combination of unique DNA sequences, including considerable variation in cox1 sequence data, thick oospore walls and physiological characteristics that appear to be adaptations favouring survival in the harsh Kwongan ecosystem suggest that these species may be endemic to Western Australia.     

Phytophthora pachypleura sp. nov., a new species causing root rot of Aucuba japonica and other ornamentals in the United Kingdom

Isolates of an unknown Phytophthora species from the ‘Phytophthora citricola complex’ have been found associated with mortality of Aucuba japonica in the UK. Based on morphological characteristics, growth–temperature relationships, sequences of five DNA regions and pathogenicity assays, the proposed novel species is described as Phytophthora pachypleura. Being homothallic with paragynous antheridia and semipapillate sporangia, P. pachypleura resembles other species in the ‘P. citricola complex’ but can be discriminated by its distinctively thick‐walled oospores with an oospore wall index of 0·71. In the phylogenetic analysis based on three nuclear (ITS, β‐tubulin, EF‐1α) and two mitochondrial (cox1, nadh1) DNA regions, P. pachypleura formed a distinct clade within the ‘P. citricola complex’ with P. citricola s. str., P. citricola E and P. acerina as its closest relatives. Phytophthora pachypleura is more aggressive to A. japonica than P. plurivora and P. multivora and has the potential to affect other ornamental species.     

A review and critical analysis of the European situation of soilborne disease management in the vegetable sector

This review concentrates on the situation of soilborne disease management on several vegetable crops with the use of different strategies, including host resistance and grafting, with special focus??based on the experience gained in Italy and Europe??on the practical problems encountered after the phaseout of methyl bromide. Special attention is given to the emergence of new diseases or the re-emergence of old ones on several crops, and on the results and problems encountered by using grafting, biofumigation and other non-chemical control methods. The search for effective, economically and environmentally sound methods for soil and substrate disinfestation remains a continuous and challenging task for growers, despite intensive research. The European Regulation No 1107/2009, concerning the placing of plant protection products on the market and the European Directive No 2009/128/EC, establishing a framework for Community action to achieve the sustainable use of pesticides, requires, by 2014, that all professional users implement the general principles of IPM. Research efforts associated with phaseout of methyl bromide generated new knowledge about the biology, ecology and management of soilborne pathogens and suggested more attention towards crop and soil health.     

Long-term storage and survival structure of three species of <Emphasis Type="Italic">Phytophthora </Emphasis>in water

 Cultures of Phytophthora cinnamomi, P. parasitica, and P. palmivora remained viable in water at room temperature for periods ranging from 6 to 23 years. The colonies that developed from the stored cultures were thin-walled and spherical, ranging from 19.2 to 30.0 μm in diameter. The survival structures are thought to be small chlamydospores produced in the absence of adequate nutrition and aeration. Received: October 7, 2002 / Accepted: January 8, 2003 Acknowledgment I thank Dr. Michael L. Parsons for assistance in preparing the photograph.     

Phytophthora bilorbang sp. nov., a new species associated with the decline of Rubus anglocandicans (European blackberry) in Western Australia

A new homothallic Phytophthora species, isolated from rhizosphere soil and roots of declining or dead Rubus anglocandicans (European blackberry) in south-west Western Australia, is described as Phytophthora bilorbang sp. nov. It produces non-papillate sporangia, smooth-walled oogonia containing thick-walled oospores, and paragynous antheridia. Although morphologically similar to several species within ITS Clade 6 and sub-clade II, namely P. gibbosa, P. gregata and P. megasperma, phylogenetic analyses of the ITS, cox1, HSP90, BT and NADH gene regions demonstrate that P. bilorbang sp. nov. is a distinct species. Additionally, P. bilorbang differs from these species in its growth and colony morphology on several media. Pathogenicity tests indicate that P. bilorbang could be responsible for the decline syndrome of blackberry within the Warren and Donnelly River catchments in the south-west of Western Australia.     

Population structure of Phytophthora infestans collected on potato and tomato in Italy

Late blight caused by the oomycete Phytophthora infestans is a disease of potato and tomato of worldwide relevance and is widespread throughout Europe and the Mediterranean region. While pathogen populations in northern Europe have been sampled and characterized for many years, the genetic structure of populations from southern Europe, including Italy, has been less studied. Between 2018 and 2019, we collected 91 samples of P. infestans from potato and tomato crops in Italy, Algeria, and Tunisia on FTA cards and genotyped them using 12-plex microsatellites. These samples were compared to genotypes of P. infestans previously collected within the framework of the EuroBlight network and from published sources. Four clonal lineages were identified: 13_A2 (Blue 13), 2_A1, 23_A1, and 36_A2. Two other isolates collected could not be matched to any currently known clonal lineage. The 13_A2 and 36_A2 lineages were found exclusively in southern Italy and Algeria, while 2_A1 was only found in Algeria. This is the first report of the 36_A2 lineage in Italy. Two isolates from Solanum nigrum were 13_A2, suggesting this weed host could be a reservoir of inoculum. The 23_A1 lineage was found widely on infected tomato crops in Italy and is the same as the lineage US-23 that is widespread in North America. Differences in genotypes across the country suggests that there may be different sources of introduction into Italy, possibly via infected seed tubers from other countries in Europe, tubers for consumption from North Africa, or tomatoes.     

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.     

青海马铃薯晚疫病菌线粒体DNA单倍型鉴定及分析

 为查明青海地区晚疫病菌单倍型分布情况,本研究对青海不同地区采自2006～2007年的70个晚疫病菌材料的线粒体单倍型进行了分析,结果表明：94.3%的菌株为Ⅱa型,5.7%的菌株为Ⅱb型,其中Ⅱb型均分离自番茄。这说明青海地区马铃薯晚疫病菌群体类型比较单一,主要为Ⅱa型,线粒体单倍型不存在多态性。     

Suppression of clubroot disease under neutral pH caused by inhibition of spore germination of Plasmodiophora brassicae in the rhizosphere

To elucidate the mechanism of clubroot suppression under neutral soil pH, a highly reproducible germination assay system under soil culture conditions was designed based on the hypothesis that germinated spores of Plasmodiophora brassicae could be identified by the absence of a nucleus (i.e. having released a zoospore to infect a root hair of the host plant). Brassica rapa var. perviridis seedlings were inoculated with a spore suspension of P. brassicae at a rate of 2·0 × 10⁶ spores g⁻¹ soil and grown in a growth chamber for 7 days. The spores were recovered from rhizosphere and non-rhizosphere soils and stained with both Fluorescent Brightener 28 (cell-wall-specific) and SYTO 82 orange fluorescent nucleic-acid stain (nucleus-specific stain). Total numbers of spores were counted under UV-excitation, and spores with a nucleus that fluoresced orange under G-excitation were counted. The significant increase in the percentage of spores without a nucleus (germinated spores) in the rhizosphere after 7 days' cultivation and the correlation with root-hair infections validated the assay system. Applications of calcium-rich compost or calcium carbonate to neutralize the soil significantly reduced the percentage of germinated spores in the rhizosphere, as well as the number of root-hair infections. The present study provides direct evidence that the inhibition of spore germination is the primary cause of disease suppression under neutral soil pH.