核桃枝枯病病原菌鉴定及其生物学特性

In May 2018,a new shoot dieback disease was found in several walnut orchards in Rizhao,Shandong Province.The fungal pathogen was obtained on PDA plate from diseased walnut shoots using a tissue isolation method.The purified fungal isolates formed white to grey colonies on PDA plate and three single spore isolates SDWa1-SDWa3 were obtained.Based on morphological characteristics and analysis of rDNA internal transcribed spacer (ITS),calmodulin (CAL),translation elongation factor 1-α (TEF1) and β-tubulin (TUB) sequences,the fungal isolates were identified as Diaporthe nobilis,a new pathogen on walnut.The test of Koch's rule confirmed that D.nobilis was the pathogen of walnut shoot dieback.To determine optimal growing conditions for the pathogen,its biological characteristics test was conducted.The results showed that the optimal growth temperature and pH value were at 25℃ and pH 5-9,respectively.The optimum carbon source was glucose,and favourable nitrogen source was peptone.     

核桃枝枯病病原菌鉴定及其生物学特性

In May 2018,a new shoot dieback disease was found in several walnut orchards in Rizhao,Shandong Province.The fungal pathogen was obtained on PDA plate from diseased walnut shoots using a tissue isolation method.The purified fungal isolates formed white to grey colonies on PDA plate and three single spore isolates SDWa1-SDWa3 were obtained.Based on morphological characteristics and analysis of rDNA internal transcribed spacer (ITS),calmodulin (CAL),translation elongation factor 1-α (TEF1) and β-tubulin (TUB) sequences,the fungal isolates were identified as Diaporthe nobilis,a new pathogen on walnut.The test of Koch's rule confirmed that D.nobilis was the pathogen of walnut shoot dieback.To determine optimal growing conditions for the pathogen,its biological characteristics test was conducted.The results showed that the optimal growth temperature and pH value were at 25℃ and pH 5-9,respectively.The optimum carbon source was glucose,and favourable nitrogen source was peptone.     

Toxic effects of acephate on Paramecium caudatum with special emphasis on morphology,behaviour, and generation time

The continuous increase in the number of new chemicals as well as the discharges of solid and liquid wastes triggered the need for simple and inexpensive bioassays for routine testing. In recent years, there has been increasing development of methods (particularly rapid tests) for testing environmental samples. This paper describes the quick toxic evaluation of an organophosphorus insecticide, acephate (O,S-dimethyl acetylphosphoramidothioate) on Paramecium caudatum for acute and sub-acute toxicity studies with reference to morphology, behaviour, and its generation time. The lethal concentrations for 10 min and 2 h were determined by probit method, as 500 mg L⁻¹ and 300 mg L⁻¹, respectively. Higher concentrations of 10 min exposure caused cell lysis with disintegration of cell membrane and precipitation of protoplasm. Combination of conventional light microscopy and computerized video tracking systems were used to study the locomotor behaviour of paramecia. The test organism was under stress and exhibited an initial increase and subsequent decrease in the swimming speed when exposed to 1/4, 1/2, 3/4, and LC₅₀ concentrations for 10 min (125, 250, 375, and 500 mg L⁻¹, respectively). Similar changes were also noticed when paramecia were exposed to LC₅₀ for 2 h. In a separate set of experiments, the number of generations and generation time in 24 h was evaluated with respect to the different sub-lethal concentrations (30, 60, 120, and 240 mg L⁻¹). The number of generations decreased and generation time extended significantly in a concentration dependent manner. The results indicate that the Paramecium toxicity assay could be used as a complimentary system to rapidly elucidate the cytotoxic potential of insecticides. The major advantages associated with these tests are: they are inexpensive, simple, user-friendly, space saving, and seem to be attractive alternatives to conventional bioassays.     

Pest survey of softwood boxes,with special emphasis on pinewood nematode,Bursaphelenchus xylophilus (Nematoda: Parasitaphelenchidae)

Wood packaging material (WPM) is an important pathway for the spread of non‐native plant pests. To reduce the likelihood of plant pest movement with WPM, the International Standard for Phytosanitary Measures No. 15: “Regulation of Wood Packaging Material in International Trade” (ISPM 15) was developed in the framework of the International Plant Protection Convention. To be compliant with this Standard, WPM shipped internationally must be either heat‐treated or fumigated, regardless of any specific characteristics of the WPM. The objective of this survey was to determine if Bursaphelenchus xylophilus (Nematoda: Parasitaphelenchidae) or insects, especially Monochamus spp. (Coleoptera: Cerambycidae), were present in a specific subset of softwood boxes. While not compliant with ISPM 15, these boxes had been treated with wood preservatives, stored indoors for over five years, and, in addition to meeting various quality standards, almost all had a moisture content below 20 percent. United States Department of Agriculture staff inspected a sample of 630 softwood boxes, focusing on those showing signs of possible pest infestation. Based on a binomial distribution with an efficacy of detection equal to 0.95, a sample size of 630 provides a 95 percent confidence of detecting pests if >0.5 % of boxes are infested. No B. xylophilus or insect pests were found in the boxes, though other nematode genera (Aphelenchoides, Aphelenchus, and Filenchus), which feed on decomposing fungi in wood and do not damage trees, were found in 21 boxes. This study demonstrates that not all types of WPM present a high phytosanitary risk. It may be worthwhile to consider an amendment to ISPM 15 to differentiate between various risk categories of WPM in order to minimize costs and environmental impacts associated with treatments currently prescribed in ISPM 15.     

Studies on the spread of the olive scab pathogen,Spilocaea oleagina1

Investigations were carried out to study the occurrence and effectiveness of wind dispersal of conidia of the olive spot pathogen Spilocaea oleagina. Dissemination in absence of rain was confirmed both by collecting conidia at various distances from an inoculum source and by using trap plants. The dispersal gradient of conidia was very steep: 3–10% of leaves of olive seedlings placed 20 m from diseased trees became infected.     

Toxic effects of acephate on Paramecium caudatum with special emphasis on morphology, behaviour, and generation time

The continuous increase in the number of new chemicals as well as the discharges of solid and liquid wastes triggered the need for simple and inexpensive bioassays for routine testing. In recent years, there has been increasing development of methods (particularly rapid tests) for testing environmental samples. This paper describes the quick toxic evaluation of an organophosphorus insecticide, acephate (O,S-dimethyl acetylphosphoramidothioate) on Paramecium caudatum for acute and sub-acute toxicity studies with reference to morphology, behaviour, and its generation time. The lethal concentrations for 10 min and 2 h were determined by probit method, as 500 mg L⁻¹ and 300 mg L⁻¹, respectively. Higher concentrations of 10 min exposure caused cell lysis with disintegration of cell membrane and precipitation of protoplasm. Combination of conventional light microscopy and computerized video tracking systems were used to study the locomotor behaviour of paramecia. The test organism was under stress and exhibited an initial increase and subsequent decrease in the swimming speed when exposed to 1/4, 1/2, 3/4, and LC₅₀ concentrations for 10 min (125, 250, 375, and 500 mg L⁻¹, respectively). Similar changes were also noticed when paramecia were exposed to LC₅₀ for 2 h. In a separate set of experiments, the number of generations and generation time in 24 h was evaluated with respect to the different sub-lethal concentrations (30, 60, 120, and 240 mg L⁻¹). The number of generations decreased and generation time extended significantly in a concentration dependent manner. The results indicate that the Paramecium toxicity assay could be used as a complimentary system to rapidly elucidate the cytotoxic potential of insecticides. The major advantages associated with these tests are: they are inexpensive, simple, user-friendly, space saving, and seem to be attractive alternatives to conventional bioassays.     

Relative humidity and wind velocity associated with diurnal rhythmicity of aerial dispersal ofPuccinia arachidis urediniospores

Four groundnut plots were inoculated withPuccinia arachidis during the growing season 1984 in Adiopodoumé (Ivory Coast). Rust intensity assessments and spore trappings were performed during the development of the resulting epidemics. Spore density in the air at canopy height ranged from 0 to 800 spores m^–3. A significant linear regression was found of the logit of the relative air spore content on the logit of rust intensity expressed as the number of lesions m^–2 of field. During the first sporulation wave following inoculation, the spore density in the air and the spore content of the pustules were determined at regular intervals. These data were related to weather parameters measured simultaneously. The spore content of the air ranged from 0 to 20 spores m^–3. A pronounced daily rhythmicity was found in the spore density of the air, related to a daily rhythm in the depletion and repletion of uredinia. The major explanatory variable was relative humidity, a secondary was wind velocity. The hypothesis is made that this periodicity affects the whole range of variation of aerial spore densities measured at different rust intensities.Samenvatting Vier veldjes met aardnoten in Adiopodoumé (Ivoorkust) werden in het groeiseizoen kunstmatig besmet metPuccinia arachidis. Gedurende het verloop van de daaropvolgende epidemie werd de mate van aantasting door roest bepaald en werden de gevangen sporen geteld. De sporendichtheid op gewashoogte varieerde van 0–800 sporen m^–3. Een significante lineaire regressie tussen de sporendichtheid en de roest-aantasting (uitgedrukt in het aantal lesies m^–2) kon worden vastgesteld na logit transformaties van de relatieve aantallen. Gedurende de eerste sporulatiegolf na de inoculatie werden de sporedichtheid in de lucht en de hoeveelheid sporen in de sporenhoopjes periodiek bepaald. De hoeveelheid sporen in de lucht varieerde van 0 tot 20 sporen m^–3. Er werd een duidelijke dagelijkse ritmiek van de sporendichtheid in de lucht gevonden. Deze hield verband met het dagelijks ritme in het verlies en de aanwas van sporen in de sporenhoopjes. De belangrijkste verklarende factor was de relatieve luchtvochtigheid, gevolgd door de windsnelheid. Er wordt verondersteld dat de gevonden periodiciteit geldt voor de gehele variatiebreedte aan sporendichtheid, bepaald bij verschillende niveaus van roestaantasting.     

Splash dispersal of Leptosphaeria maculans pycnidiospores and the spread of blackleg on oilseed rape

The fungus Leptosphaeria maculans causes blackleg (phoma stem canker), one of the most serious diseases of oilseed rape. The role of pycnidiospores produced during asexual reproduction is poorly documented and limits the understanding of the pathogen's population dynamics. The objectives of this study were to assess rain-splash dispersal of pycnidiospores of L. maculans from phoma leaf spots, and transmission of the disease from oilseed rape stubble carrying pycnidia. The work was conducted in still air with either a drop generator or a rain simulator. The impact of simulated incident drops on phoma leaf spots resulted in the dispersal of L. maculans pycnidiospores within splash droplets. Ninety per cent of the spores were collected within 14 cm of the source and a few were regularly observed up to 40 cm. Pycnidiospores produced on oilseed rape stubble and dispersed by simulated rain infected oilseed rape trap plants in a spatial pattern that matched the spatial dispersal of the pycnidiospores. In the field, rain-splash dispersal of pycnidiospores could increase the pathogen population and may enhance sexual reproduction by facilitating the mating of initially spatially separated isolates of opposite mating type.     

Evolution of gene-for-gene systems in metapopulations: the effect of spatial scale of host and pathogen dispersal

The concept of gene-for-gene coevolution is a major model for research on disease resistance in crop plants. However, few theoretical or empirical studies have examined such systems in natural situations, and as a consequence, there is little knowledge of how spatial effects are likely to influence the evolution of host resistance and pathogen virulence in gene-for-gene interactions. In this work, a simulation approach was used to investigate the epidemiological and genetic consequences of varying host and pathogen dispersal in metapopulation situations. The results demonstrate clear impacts of dispersal distance on the total number of host and pathogen genotypes that are maintained, as well as on genetic variation at individual host resistance and pathogen virulence loci. Several other important results also emerged from this study. In contrast to the predictions of many earlier nonspatial models, so-called 'super-races' of pathogens do not always evolve and dominate, indicating that it is not necessary to assume costs of resistance or virulence to maintain high levels of polymorphism in biologically realistic situations. The rate of evolution of both resistance and virulence depend on the scale of dispersal, with greater mixing (as a function of dispersal scale) resulting in a faster approach to a dynamic endpoint. The model in this paper also predicts that, despite the greater total genotypic diversity of pathogens across the metapopulation, variation in host resistance will generally be greater than variation in pathogen virulence within local populations.     

Understanding the effects of multiple sources of seasonality on the risk of pathogen spread to vineyards: vector pressure,natural infectivity,and host recovery

Seasonality plays an important role in the dynamics of infectious disease. For vector‐borne pathogens, the effects of seasonality may be manifested in the variability in vector abundance, vector infectiousness, and host‐infection dynamics over the year. The relative importance of multiple sources of seasonality on the spread of a plant pathogen, Xylella fastidiosa, into vineyards was explored. Observed seasonal population densities of the primary leafhopper vector, Graphocephala atropunctata, from 8 years of surveys in northern California were incorporated into a model of primary spread to estimate the risk of pathogen infection under different scenarios regarding seasonality in vector natural infectivity (i.e. constant or increasing over the season) and grapevine recovery from infection (i.e. none or seasonal recovery). The extent to which local climatic conditions affect risk estimates via differences in vector abundance was investigated. Seasonal natural infectivity, seasonal recovery, and especially the combination, reduced (up to 8‐fold on average) within‐season and cumulative yearly estimates of pathogen spread. Estimated risk of infection also differed greatly among years due to large differences in vector abundance, with wet and moderate winter and spring conditions favouring higher G. atropunctata abundance. Seasonal variation of the pathogen–vector interaction may play an important role in the dynamics of disease in vineyards, reducing the potential prevalence from what it could be in their absence. Moreover, climate, by affecting sharpshooter leafhopper abundance or activity, may influence Pierce’s disease dynamics.     

The effects of dispersal gradient and pathogen life cycle components on epidemic velocity in computer simulations

ABSTRACT The velocity of expansion of focal epidemics was studied using an updated version of the simulation model EPIMUL, with model parameters relevant to wheat stripe rust. The modified power law, the exponential model, and Lambert's general model were fit to primary disease gradient data from an artificially initiated field epidemic of stripe rust and employed to describe dispersal in simulations. The exponential model, which fit the field data poorly (R (2) = 0.728 to 0.776), yielded an epidemic that expanded as a traveling wave (i.e., at a constant velocity), after an initial buildup period. Both the modified power law and the Lambert model fit the field data well (R(2) = 0.962 to 0.988) and resulted in dispersive epidemic waves (velocities increased over time for the entire course of the epidemic). The field epidemic also expanded as a dispersive wave. Using parameters based on the field epidemic and modified power law dispersal as a baseline, life cycle components of the pathogen (lesion growth rate, latent period, infectious period, and multiplication rate) and dispersal gradient steepness were varied within biologically reasonable ranges for this disease to test their effect on dispersive wave epidemics. All components but the infectious period had a strong influence on epidemic velocity, but none changed the general pattern of velocity increasing over time.     

Long‐term viability of the northern anthracnose pathogen,Kabatiella caulivora,facilitates its transportation and spread

The conidia and resting hyphae of the northern anthracnose pathogen of Trifolium species, Kabatiella caulivora, were effectively carried by, and maintained long‐term viability on, a range of materials, including metals, fabrics, woods and plastics. Conidia and hyphae became thick‐walled and melanized with time. There were significant (P < 0.001) differences in conidia/resting hyphae survival between carrier materials and between temperature regimes. At 23 °C/8 °C day/night, conidia and resting hyphae remained viable on steel, corrugated iron, galvanized steel, all tested fabrics, wood and random mixed materials for up to 8 months. At 36 °C/14 °C day/night, conidia and resting hyphae remained viable for up to 8 months, but only on cotton, denim, fleece, silk, leather, paper, plastic and all wood materials. At 45 °C/15 °C day/night, conidia and resting hyphae remained viable up to 8 months only on fleece wool, Eucalyptus marginata (jarrah wood) and paper. There were significant differences between carrier materials in their abilities to retain conidia and resting hyphae after washing (P < 0.001). Metabolic activity was confirmed for conidia and resting hyphae recovered after 8 months and K. caulivora colonies successfully re‐established on potato dextrose agar. Findings confirmed the critical importance of materials as long‐term carriers of viable K. caulivora conidia and resting hyphae, highlighting the potential for spread of a highly virulent K. caulivora race within and outside Australia via farming equipment, clothing and other associated materials. Results also have wider biosecurity implications for the transportation of fungal‐infested carrier materials previously considered as low risk.     

Further spread of the gypsy moth fungal pathogen,Entomophaga maimaiga,to the west and north in Central Europe

Journal of Plant Diseases and Protection - The gypsy moth, Lymantria dispar, is one of the most important pests of deciduous trees in Europe, occurring in all environmental zones of Europe except...     

Alternative hosts and plant tissues for the survival,sporulation and spread of the Ascochyta blight pathogen of chickpea

Various crop and weed species were infected naturally by Didymella rabiei (anamorph: Ascochyta rabiei) in blight-affected chickpea fields in the Palouse region of eastern Washington and northern Idaho, USA. The fungus was isolated from asymptomatic plants of 16 species commonly found in commercial crops in this region. Isolates of the pathogen from crop and weed species were pathogenic to chickpea and indistinguishable in cultural and morphological characteristics from isolates of D. rabiei from chickpea. Both mating types of D. rabiei were isolated from eight naturally infected plant species. Chickpeas were infected by D. rabiei when plants emerged through infested debris of seven crop and weed species. The teleomorph developed on overwintered tissues of seven plant species infected naturally by D. rabiei in a blight screening nursery and on debris of wheat, white sweet clover and pea inoculated with ascospores of D. rabiei or conidia of two compatible isolates of the pathogen. Didymella rabiei naturally infected 31 accessions of 12 Cicer spp. and the teleomorph developed on the overwintered debris of all accessions, including those of three highly resistant perennial species. The fungus developed on the stem and leaf pieces of ten plant species common to southern Spain inoculated with conidia of two compatible isolates of D. rabiei, and formed pseudothecia with asci and viable ascospores on six of ten species and pycnidia with conidia on all plant species.     

Pervasive fungicide resistance in Botrytis from strawberry in Norway: Identification of the grey mould pathogen and mutations

Control of grey mould, caused by Botrytis spp., is a major challenge in open field strawberry production. Botrytis was isolated from plant parts collected from 19 perennial strawberry fields with suspected fungicide resistance in the Agder region of Norway in 2016. Resistance to boscalid, pyraclostrobin and fenhexamid was high and found in 89.1%, 86.0% and 65.4% of conidia samples, respectively. Multiple fungicide resistance was common; 69.6% of conidia samples exhibited resistance to three or more fungicides. Botrytis group S and B. cinerea sensu stricto isolates were obtained from 19 and 16 fields, respectively. The sdhB, cytb, erg27 and mrr1 genes of a selection of isolates were examined for the presence of mutations known to confer fungicide resistance to boscalid, pyraclostrobin, fenhexamid and pyrimethanil plus fludioxonil, respectively. Allele-specific PCR assays were developed for efficient detection of resistance-conferring mutations in cytb. Among B. cinerea isolates, 84.7%, 86.3% and 61.3% had resistance-conferring mutations in sdhB, cytb and erg27, respectively. A triplet deletion in mrr1, resulting in ΔL497, commonly associated with the multidrug resistance phenotype MDR1h, was detected in 29.2% of Botrytis group S isolates. High frequencies of resistance to several fungicides were also detected in Botrytis from both imported and domestically produced strawberry transplants. Fungicide resistance frequencies were not different among fields grouped by level of grey mould problem assessed by growers, indicating factors other than fungicide resistance contributed to control failure, a fact that has important implications for future management of grey mould.     

Effects of dieback on the vegetative,chemical, and physiological status of mangrove forests,Iran

Mangrove forests are valuable resources in tropical and subtropical regions, which have been faced dieback due to various human activities including rapid expansion of shrimp farming, urban development, and pollution, as well as natural factors such as rising sea level, increasing air temperature, drought, and sharp decrease in rainfall. However, the mechanisms of dieback of mangrove forests are not well understood. Therefore, this research aimed to assess the vegetative, chemical, and physiolog...     

Post-genomics of microsporidia, with emphasis on a model of minimal eukaryotic proteome: a review

The genome sequence of the microsporidian parasite Encephalitozoon cuniculi Levaditi, Nicolau et Schoen, 1923 contains about 2,000 genes that are representative of a non-redundant potential proteome composed of 1,909 protein chains. The purpose of this review is to relate some advances in the characterisation of this proteome through bioinformatics and experimental approaches. The reduced diversity of the set of E. cuniculi proteins is perceptible in all the compilations of predicted domains, orthologs, families and superfamilies, available in several public databases. The phyletic patterns of orthologs for seven eukaryotic organisms support an extensive gene loss in the fungal clade, with additional deletions in E. cuniculi. Most microsporidial orthologs are the smallest ones among eukaryotes, justifying an interest in the use of these compacted proteins to better discriminate between essential and non-essential regions. The three components of the E. cuniculi mRNA capping apparatus have been especially well characterized and the three-dimensional structure of the cap methyltransferase has been elucidated following the crystallisation of the microsporidial enzyme Ecm1. So far, our mass spectrometry-based analyses of the E. cuniculi spore proteome has led to the identification of about 170 proteins, one-quarter of these having no clearly predicted function. Immunocytochemical studies are in progress to determine the subcellular localisation of microsporidia-specific proteins. Post-translational modifications such as phosphorylation and glycosylation are expected to be soon explored.