Showing papers in "European Journal of Plant Pathology in 2003"
TL;DR: The names, abbreviations and synonyms of the whitefly-transmitted viruses are presented in tabulated form together with details of their whitefly vectors, natural hosts and distribution.
Abstract: One-hundred and fourteen virus species are transmitted by whiteflies (family Aleyrodidae). Bemisia tabaci transmits 111 of these species while Trialeurodes vaporariorum and T. abutilonia transmit three species each. B. tabaci and T. vaporariorum are present in the European–Mediterranean region, though the former is restricted in its distribution. Of the whitefly-transmitted virus species, 90% belong to the Begomovirus genus, 6% to the Crinivirus genus and the remaining 4% are in the Closterovirus, Ipomovirus or Carlavirus genera. Other named, whitefly-transmitted viruses that have not yet been ranked as species are also documented. The names, abbreviations and synonyms of the whitefly-transmitted viruses are presented in tabulated form together with details of their whitefly vectors, natural hosts and distribution. Entries are also annotated with references. Whitefly-transmitted viruses affecting plants in the European–Mediterranean region have been highlighted in the text.
822 citations
TL;DR: This review deals with the influence of climate on the production and dispersal of inocula, growth, competition, mycotoxin production and pathogenicity of Fusarium diseases of small-grain cereals.
Abstract: Fusarium head blight of small-grain cereals, ear rot of maize, seedling blight and foot rot of cereals are important diseases throughout the world.Fusarium graminearum, F. culmorum, F. poae, F. avenaceum and Microdochium nivale (formerly known as F. nivale) predominantly cause Fusarium diseases of small-grain cereals. Maize is predominantly attacked by F. graminearum, F. moniliforme, F. proliferatum and F. subglutinans. These species differ in their climatic distribution and in the optimum climatic conditions required for their persistence. This review deals with the influence of climate on the production and dispersal of inocula, growth, competition, mycotoxin production and pathogenicity. Most species produce inocula, grow best, and are most pathogenic to cereal heads at warm temperatures and under humid conditions. However, the optimal conditions for F. moniliforme and F. proliferatum maize ear rot tend to be hot and dry andM. nivale head blight, seedling blight and foot rot of small-grain cereals tend to occur under cooler conditions. Seedling blight and foot rot caused by other species are favoured by warm dry weather. Between them, these fungi produce four important classes of mycotoxins: trichothecenes, zearalenone, fumonisins and moniliformin. Conditions favourable for in vitro growth are also generally the most favourable for mycotoxin production on cereal grains. These fungi rarely exist in isolation, but occur as a complex with each other and with otherFusaria and other fungal genera. Climatic conditions will influence competition between, and the predominance of, different fungi within this complex.
366 citations
TL;DR: Recent data on the epidemiology of the common mycotoxigenic species of Fusarium, Alternaria, Aspergillus and Penicillium in infected or colonized plants, and in stored or processed plant products from the Mediterranean area are reviewed.
Abstract: Recent data on the epidemiology of the common mycotoxigenic species of Fusarium, Alternaria, Aspergillus and Penicillium in infected or colonized plants, and in stored or processed plant products from the Mediterranean area are reviewed. Emphasis is placed on the toxigenicity of the causal fungal species and the natural occurrence of well known mycotoxins (aflatoxins, ochratoxins, fumonisins, trichothecenes, zearalenone, patulin, Alternaria-toxins and moniliformin), as well as some more recently described compounds (fusaproliferin, beauvericin) whose toxigenic potential is not yet well understood. Several Fusarium species reported from throughout the Mediterranean area are responsible of the formation of mycotoxins in infected plants and in plant products, including: Fusarium graminearum, F. culmorum, F. cerealis, F. avenaceum, F. sporotrichioides and F. poae, which produce deoxynivalenol, nivalenol, fusarenone, zearalenone, moniliformin, and T-2 toxin derivatives in wheat and other small grains affected by head blight or scab, and in maize affected by red ear rot. Moreover, strains of F. verticillioides, F. proliferatum, and F. subglutinans, that form fumonisins, beauvericin, fusaproliferin, and moniliformin, are commonly associated with maize affected by ear rot. Fumonisins, were also associated with Fusarium crown and root rot of asparagus and Fusarium endosepsis of figs, caused primarily by F. proliferatum. Toxigenic A. alternata strains and associated tenuazonic acid and alternariols were commonly found in black mould of tomato, black rot of olive and citrus, black point of small cereals, and black mould of several vegetables. Toxigenic strains of A. carbonarius and ochratoxin A were often found associated with black rot of grapes, whereas toxigenic strains of A. flavus and/or P. verrucosum, forming aflatoxins and ochratoxin A, respectively, were found in moulded plant products from small cereals, peanuts, figs, pea, oilseed rape, sunflower seeds, sesame seeds, pistachios, and almonds. Finally, toxigenic strains of P. expansum and patulin were frequently found in apple, pear and other fresh fruits affected by blue mould rot, as well as in derived juices and jams.
356 citations
TL;DR: A diagnostic PCR method was developed to detect the most common species of Fusarium occurring on wheat, and demonstrated that F. graminearum was the most abundant species in the FUSarium complex on wheat in both years.
Abstract: The re-emergence of fusarium head blight throughout the world and especially in Western Europe prompted a survey of the situation in the Netherlands. To allow for a high throughput screening of large numbers of samples, a diagnostic PCR method was developed to detect the most common species of Fusarium occurring on wheat. Seven primer pairs were tested for their ability to identify isolates of Fusarium avenaceum, F. culmorum, F. graminearum, F. poae, F. proliferatum and Microdochium nivale var. majus and M. nivale var. nivale. Each primer pair only generated a PCR product with the corresponding Fusarium species and all PCR fragments had different molecular sizes. This allowed the generation of these amplicons using a mixture of all seven primer pairs. The robustness of this multiplex PCR encouraged us to screen a large series of isolates collected in 2000 and 2001. In both years 40 fields were sampled leading to a collection of 209 isolates from 2000 and 145 isolates from 2001. The results of the multiplex PCR demonstrated that F. graminearum was the most abundant species in the Fusarium complex on wheat in both years. This is in sharp contrast to reports from the 1980s and early 1990s, which found F. culmorum as the predominant species. Primers derived from the tri7 and tri13 genes, which are implicated in the acetylation and oxygenation of the C-4 atom of the backbone of the trichothecene molecule, were used to discriminate between deoxynivalenol and nivalenol (NIV) producers. The populations of F. culmorum and F. graminearum both showed a slight increase in NIV-producers in 2001.
329 citations
TL;DR: Progress is being made toward accurate models for risk assessment of both diseases, but key challenges remain in terms of integrating models of pre- and post-infection events, quantifying the roles of insects in these diseases, and characterizing interactions among competing fungi and the environment.
Abstract: Fusarium species cause two distinct diseases on ears of maize, Fusarium ear rot (or pink ear rot) and Gibberella ear rot (or red ear rot), both of which can result in mycotoxin contamination of maize grain. The primary causal agent for Fusarium ear rot is Fusarium verticillioides, but F. subglutinans and F. proliferatum are also important. Gibberella ear rot is caused primarily by F. graminearum, but F. culmorum can also be important, especially in Europe. Aspects of the epidemiology of both diseases have been studied for decades, but only recently have efforts been made to synthesize this information into comprehensive models of disease development. Much of the work on F. graminearum has focused on Fusarium head blight of small-grain crops, but some of the results obtained are also relevant to maize. The primary mycotoxins produced by these fungi, fumonisins and deoxynivalenol, have differing roles in the disease-cycle, and these roles are not completely understood, especially in the case of fumonisins. Progress is being made toward accurate models for risk assessment of both diseases, but key challenges remain in terms of integrating models of pre- and post-infection events, quantifying the roles of insects in these diseases, and characterizing interactions among competing fungi and the environment.
326 citations
TL;DR: A more holistic ecological view is needed when considering management approaches to long-term-safe storage of cereal grains after harvest.
Abstract: Grain quality after harvest is influenced by a wide variety of abiotic and biotic factors and has been studied as a stored grain ecosystem. Important factors include grain and contaminant mould respiration, insects and mites, and the key environmental factors of water availability and temperature. Interactions between these factors influence the dominance of fungi, particularly mycotoxigenic species. Studies have shown that growth, mycotoxin production, competitiveness and niche occupation by mycotoxigenic species are influenced by the presence of other contaminant moulds and environmental factors. This has been demonstrated for both Fusarium culmorum and deoxynivalenol production, Aspergillus ochraceus/Penicillium verruscosum and ochratoxin production and Fusarium section Liseola and fumonisin production. Interactions between mycotoxigenic spoilage fungi and insects do occur but have not been studied thoroughly. Some insects disseminate mycotoxigenic species, others are known to use spoilage moulds as a food source, while others avoid certain fungal species. Thus, a more holistic ecological view is needed when considering management approaches to long-term-safe storage of cereal grains after harvest.
320 citations
TL;DR: The race structure of L. maculans was assessed on the basis of the analysis of 1011 isolates collected in France between 1990 and 2000, and it was suggested that the development of integrated strategies aiming at maximising the durability of novel resistance is now a priority for this pathosystem.
Abstract: Leptosphaeria maculans, the cause of stem canker of oilseed rape (OSR), exhibits gene-for-gene interactions with its host plant. The race structure of L. maculans was assessed on the basis of the analysis of 1011 isolates collected in France between 1990 and 2000, with regards to three AVR genes, AvrLm1, AvrLm2 and AvrLm4. The effect of selection pressure, due to large-scale cropping of Rlm1 cultivars, on the evolution of races of the fungus was also evaluated. The results revealed a scarcity or complete absence of isolates harbouring AvrLm2, whereas isolates harbouring AvrLm4 were present at a variable level, that was as high as 17.2–31.2% depending on the sample year and location. When obtained from rlm1 cultivars, isolates harbouring AvrLm1 always represented more than 83% of the populations until the 1997–1998 growing season. As a consequence, the Rlm1 cultivars had been highly efficient at controlling the disease and were grown on an estimated 43.7% of the total French acreage in OSR in 1998–1999. However, the increased commercial success of Rlm1 cultivars was paralleled by a decrease in the proportion of isolates harbouring AvrLm1 in 1997–1998 and 1998–1999. This resulted in less than 13% of isolates harbouring AvrLm1 in populations being collected from rlm1 cultivars in 1999 and 2000, and contributed to the loss of efficiency of the Rlm1 resistance in the field. The present study is an illustration of one round of a `boom and bust' cycle that occurred for a pathosystem where it has never been reported before. These data and the high evolutionary potential of L. maculans are fully supportive of one pathogen species with a high risk of breaking down resistance genes in OSR and suggest that the development of integrated strategies aiming at maximising the durability of novel resistance is now a priority for this pathosystem.
222 citations
TL;DR: This review seeks to summarise the significance of FHB and review the effectiveness of cultural, biological and chemical control strategies that have been investigated for the control of the disease.
Abstract: Fusarium head blight (FHB) is a widespread and destructive disease of small grained cereals caused by a number of Fusarium species and Microdochium nivale. In addition to causing significant reductions in grain yield, FHB can result in the reduction of grain quality, either by affecting grain processing qualities or by producing a range of toxic metabolites that have adverse effects on humans and livestock. Control of FHB can be achieved by a number of cultural, biological and chemical strategies along with the exploitation of host plant resistance. In recent years, much of the research undertaken for the control of FHB has been concentrated on understanding and exploiting the genetic resistance of cereal plants to FHB-causing pathogens. Although, a brief overview of genetic resistance is presented, this review seeks to summarise the significance of FHB and review the effectiveness of cultural, biological and chemical control strategies that have been investigated for the control the disease.
177 citations
TL;DR: F. graminearum and F. culmorum were the most pathogenic of the five species, causing at least a 69% reduction in coleoptile growth at 10, 15, 20 and 25 °C, and general linear model analysis showed that species accounted for 51.3–63.4% of the variation in isolate growth.
Abstract: The effect of temperature on the in vitro growth rates and pathogenicity of a European Fusarium collection consisting of isolates of Fusarium graminearum,F culmorum,F avenaceum, F poae and Microdochium nivale was examined Irrespective of geographic origin, the optimum temperature for the growth of F graminearum, F culmorum and F poae was 25 °C, while that for F avenaceum and M nivale was 20 °C In general, the growth rates of F graminearum, F culmorum and F poae increased between 10 and 25 °C and those of F avenaceum and M nivale increased between 10 and 20 °C Pathogenicity tests were carried out by examining the effect of the five species on the in vitro coleoptile growth rate of wheat seedlings (cv Falstaff) Irrespective of geographic origin, the temperature at which F avenaceum, F culmorum and F graminearum caused the greatest retardation in coleoptile growth ranges 20–25 °C (>893% reduction), whilst for F poae and M nivale it was 10–15 °C (>456% retardation), relative to uninoculated control seedlings In general, F culmorum and F graminearum were the most pathogenic of the five species, causing at least a 69% reduction in coleoptile growth at 10, 15, 20 and 25 °C General linear model analysis (GLIM) showed that species accounted for 513–634% of the variation in isolate growth and from 195% to 443% of the variation in in vitro pathogenicity Country of origin contributed from 226% to 519% to growth rate variation and from 073% to 761% to pathogenicity variation The only significant correlation between in vitro growth and pathogenicity was that observed for M nivale at 15 °C (r = -0803, P < 005)
169 citations
TL;DR: Results show that the antagonistic activity of HS93, LS674 and T. harzianum may be stimulated by chitin resulting in significant improvements in their effectiveness against pathogens.
Abstract: Two bacterial isolates and one strain of Trichoderma harzianum were tested alone and in combination with chitin for efficacy in control of root rot disease caused by Phytophthora capsici and Rhizoctonia solani in pepper plants under greenhouse conditions. These bacteria (Bacillus subtilis HS93 and B. licheniformis LS674) were isolated from repeatedly washed roots of pepper plants. In in vitro assays, HS93, LS674 and T. harzianum were antagonistic against P. capsici and R. solani and produced high levels of chitinase. Seed treatment and root drenching with bacterial suspensions of HS93 with 0.5% chitin was more effective against Phytophthora and Rhizoctonia root rot than addition of the organisms without chitin. LS674 and T. harzianum reduced Rhizoctonia but not Phytophthora root rot. In two greenhouse tests, seed treatment and root drenching with HS93 amended with chitin enhanced its biocontrol activity against P. capsici but not on R. solani. The effects of LS674 and T. harzianum against R. solani were significantly enhanced when they were used as suspensions with 0.5% chitin for root drenching, but this had no effect on P. capsici. In both greenhouse experiments, the use of 0.5% chitin alone for root drenching reduced Rhizoctonia root rot. Reduction of root rot disease was accompanied by increased yield. These results show that the antagonistic activity of HS93, LS674 and T. harzianum may be stimulated by chitin resulting in significant improvements in their effectiveness against pathogens.
157 citations
TL;DR: Yield-loss under different rates of progress of yellow spot and septoria nodorum blotch was examined in four experiments over three years to define the relationship between disease severity and yield and provided information towards the development of disease management strategies for the control of septorian blotch and yellow spot.
Abstract: Yellow or tan spot (caused by Pyrenophora tritici-repentis) and septoria nodorum blotch (caused by Phaeosphaeria nodorum) occur together and are a constraint to wheat yields in Australia. Recently, higher crop yields and lower fungicide costs have made fungicides an attractive management tool against these diseases. Yield-loss under different rates of progress of yellow spot and septoria nodorum blotch was examined in four experiments over three years to define the relationship between disease severity and yield. In these experiments, differences in disease were first promoted by inoculations either with P. tritici-repentis-infected stubble or aqueous spore suspensions of P. nodorum. Disease progress was further manipulated with foliar application of fungicide. The pattern of disease development varied in each year under the influence of different rainfall patterns. The inoculation and fungicide treatments produced differences in disease levels after flag leaf emergence. The infection of yellow spot or septoria nodorum blotch caused similar losses in grain yield, ranging from 18% to 31%. The infection by either disease on the flag or penultimate leaf provided a good indication of yield-loss. Disease severity on flag leaves during the milk stage of the crop or an integration of disease as area under the disease progress curve on the flag leaves based on thermal time explained more than 80% variance in yield in a simple regression model. The data provided information towards the development of disease management strategies for the control of septoria nodorum blotch and yellow spot.
TL;DR: Research on the epidemiology of Fusarium ear (or head) blight of small-grain cereals is reviewed, focusing on inoculum, infection and disease forecasting, and it is confirmed that warm and moist conditions during anthesis are the key factors for FEB development.
Abstract: Recent research on the epidemiology of Fusarium ear (or head) blight (FEB or FHB) of small-grain cereals is reviewed, focusing on inoculum, infection and disease forecasting. Both conidia and ascospores have been shown to be important for causing FEB. For Fusarium graminearum, propagules from crop debris are the main source of initial inoculum. Inoculum production is critically dependent on rainfall although the precise relationship is not clear. Recent work on understanding the effects of climatic variables on FEB development has been based on field observations. These field-based studies confirmed that warm and moist conditions during anthesis are the key factors for FEB development. Several empirical models were derived from the field data and proposed for use in disease forecasting. However, these models may not be applicable to a broader range of areas because of the limited nature of the field data. Several areas are proposed for future research, focusing on the development of more generally applicable forecasting models and on understanding the relationships between disease severity, fungal biomass and the production of associated mycotoxins.
TL;DR: The results suggest that meteorological differences between years and grape-growing areas are responsible for differences in OTA levels, but the data are at present insufficient to draw firm conclusions.
Abstract: Fungi responsible for ochratoxin A (OTA) production have been studied especially on cereals, where Penicillium verrucosum and Aspergillus ochraceus are to be considered the main producers. Until 1998, these fungi were also believed to be responsible for the production of the toxin in grape, but OTA-producing A. carbonarius and A. niger were identified in dried vine fruits in 1999. Further studies pointed out that mycoflora potentially responsible for the presence of OTA in grapes are present in the field. Aspergilli are dominant to Penicillia, and among these Aspergilli section Nigri. A. carbonarius probably plays an important role because of the high percentage of positive strains and the amount of OTA produced. Aspergilli section Nigri are present on grape bunches early in the season and their frequency increases during later growth stages. At early veraison and ripening, the incidence of colonised berries is more related to the year than to the growth stage, but not to visible symptoms, since it is normal to isolate fungi from intact berries. Differences in ochratoxin content of berries have been detected between years, when the same vineyards, managed in the same way, showed high levels (1999) or the absence (2000) of the toxin. The results suggest that meteorological differences between years and grape-growing areas are responsible for differences in OTA levels, but the data are at present insufficient to draw firm conclusions.
TL;DR: Common methodologies that are used to quantify and model spatio-temporal dynamics of plant diseases, with emphasis on developing temporal forecast models and on quantifying spatial patterns are outlined.
Abstract: An epidemic is the progress of disease in time and space. Each epidemic has a structure whose temporal dynamics and spatial patterns are jointly determined by the pathosystem characteristics and environmental conditions. One of the important objectives in epidemiology is to understand such spatio-temporal dynamics via mathematical and statistical modelling. In this paper, we outline common methodologies that are used to quantify and model spatio-temporal dynamics of plant diseases, with emphasis on developing temporal forecast models and on quantifying spatial patterns. Several examples of epidemiological models in cereal crops are described, including one for Fusarium head blight.
TL;DR: Results show that, although AG 3 is the most common R. solani group on potato in France, AG 5 and AG 2-1 may be present, and isolates were highly sensitive to flutolanil, iprodione and pencycuron, except the AG 5 isolates, moderately sensitive to pencyCuron.
Abstract: A collection of 241 isolates of Rhizoctonia solani obtained from potato plants grown in different areas in France was characterized for anastomosis grouping, symptomatology on tubers of different cultivars and sensitivity to three fungicides. Most isolates collected belonged to (anastomosis groups (AGs)) AG 3, but 2% and 4% of the isolates were AG 5 and AG 2-1. AG 3 and AG 2-1 isolates were mostly obtained from sclerotia on tubers, but all AG 5, some AG 3 and some AG 2-1 isolates were recovered from superficial tuber alterations, like deformations, corky or scabby lesions. Sclerotia were formed on tubers produced by healthy stem cuttings grown in soil artificially infested with AG 3, but not on tubers grown in soil infested with either AG 5 or AG 2-1. No variation in susceptibility to sclerotial formation was observed among five potato cultivars. In all cases, a large proportion of tubers showed superficial corky lesions, often associated with deformations. The proportion of tubers with lesions and deformations was highest in soil infested with AG 2-1 and significantly lower on cv. Samba in all treatments. All isolates were highly sensitive to flutolanil, iprodione and pencycuron, except the AG 5 isolates, moderately sensitive to pencycuron. These results show that, although AG 3 is the most common R. solani group on potato in France, AG 5 and AG 2-1 may be present. Isolates differed for pathogenicity. In vitro sensitivity to fungicides varied among AGs.
TL;DR: This is the first report of GLRaV-1 and -3 transmission by mealybug and coccid species in France, and the first reports of the ability of H. bohemicus and Phenacoccus aceris to transmit these viruses to grapevines.
Abstract: Many grape viruses, such as filamentous Grapevine leafroll-associated viruses in the Closteroviridae family, are spread primarily through infected propagating material. However, there is increasing evidence that leafroll disease are spread in the field by insect vectors, namely mealybugs and other scale insects. This study was carried out in the northern wine-growing regions of France where Grapevine leafroll-associated virus-1 and -3 (GLRaV-1 and -3) are the most widespread grape Ampelovirus species. The vineyards were inspected for presence of mealybug and scale insects and grapes infected by GLRaV-1 and -3. Mealybugs, Heliococcus bohemicus, Phenacoccus aceris (Pseudococcidae) and the soft scale insect Parthenolecanium corni (Coccidae), were capable of a transmission efficiency of 14%, 23% and 29% respectively. GLRaV-1 and -3 infections that resulted from virus transmission were confirmed with DAS-ELISA using polyclonal antibodies. This is the first report of GLRaV-1 and -3 transmission by mealybug and coccid species in France, and the first report of the ability of H. bohemicus and Phenacoccus aceris to transmit these viruses to grapevines. The relevance of these findings with regards to maintenance of virus-free grapevine stocks and to control leafroll spread in commercial vineyards is discussed.
TL;DR: Diagnostic and quantitative polymerase chain reaction assays have been developed to detect and quantify individual fungal species within the disease complex and, where relevant, to differentiate between chemotypes within a single species.
Abstract: Fusarium head blight (FHB) of cereals is a disease complex. Fusarium graminearum is the major pathogen worldwide, while F. culmorum, F. avenaceum and F. poae are also associated with this disease. In addition to the true Fusarium species, Microdochium nivale may also cause head blight and is particularly prevalent where cooler, wetter conditions prevail. Other species such as F. sporotrichioides, F. equiseti and even F. verticillioides may also be of significance in particular situations. FHB is of particular concern because of the ability of the Fusarium species to produce mycotoxins in the grain that are harmful to human and animal consumers. The predominant mycotoxins within cereals are the trichothecenes, chiefly deoxynivalenol, nivalenol and their acetylated derivatives, along with T-2, HT-2, diacetoxyscirpenol and neosolaniol. This paper reviews the use of molecular techniques to identify the individual causal agents and to quantify their relative amounts within plant tissue. Diagnostic and quantitative polymerase chain reaction assays have been developed to detect and quantify individual fungal species within the disease complex and, where relevant, to differentiate between chemotypes within a single species. Assays to determine the type of toxin produced, or monitor the regulation of toxin production also provide valuable tools for understanding this disease. These techniques are being used to dissect the disease complex into its component parts in order to study interactions between the pathogens and their host and between the pathogens themselves as well as to determine the influence of environmental factors on the disease and the toxins produced by these fungi.
TL;DR: The genus name Tapesia is now rejected in favour of the conserved name Mollisia, which appears to comprise heterogeneous fungi, and a new holomorph genus, Oculimacula, is proposed for teleomorphs of the eyespot fungi, while the anamorphs are accommodated in Helgardia gen. nov.
Abstract: Four species so far classified in Pseudocercosporella or Ramulispora (hyphomycetes) are associated with eyespot disease symptoms of cereals. Two of these have been linked to teleomorphs that were described in Tapesia. Sequence data derived from the Internal Transcribed Spacer region (ITS1, 5.8S and ITS2) of the rDNA operon showed, however, that the eyespot fungi associated with Tapesia are not congeneric with Ramulispora sorghi, the type of Ramulispora. The genus name Tapesia is now rejected in favour of the conserved name Mollisia, which appears to comprise heterogeneous fungi. Tapesia yallundae is not closely related to the type of Mollisia, M. cinerea ,b ut clusters separately, being more closely allied to species with Cadophora anamorphs. A new holomorph genus, Oculimacula, is therefore proposed for teleomorphs of the eyespot fungi, while the anamorphs are accommodated in Helgardia gen. nov.
TL;DR: A significant negative correlation was established between virulence and mycelial growth rate, and the grapevine leaves were significantly more susceptible to B. cinerea than those of tobacco.
Abstract: One hundred and twenty-one single-spore strains of Botrytis cinerea isolated from Bordeaux vineyards were molecularly characterized as either transposa or vacuma, two subpopulations of B. cinerea distinguished by the presence of transposable elements. Forty-three vacuma and 68 transposa strains were distributed into two main classes (mycelial or sclerotial) by morphological phenotype according to the organ of origin. Strains isolated from overwintering sclerotia produced exclusively sclerotial colonies. The mycelial growth rate of 21 transposa and 13 vacuma strains was significantly influenced by agar-medium and temperature. The mycelial growth rate was significantly strain-dependent at favourable temperatures (15, 20 and 25 °C), but not at limiting ones (5 and 28 °C): vacuma strains showed the fastest growth rates. The strains of the two subpopulations were similar in virulence on both host species tested (Vitis vinifera and Nicotiana clevelandii). The grapevine leaves were significantly more susceptible to B. cinerea than those of tobacco. A significant negative correlation was established between virulence and mycelial growth rate. The epidemiological consequences concerning population structure of B. cinerea in vineyards are discussed.
TL;DR: A high throughput DNA extraction method, that allowed molecular analysis of this obligate pathogen directly in the host without any isolation procedure, was developed.
Abstract: The Oomycete Plasmopara viticola is the causal organism of downy mildew on grapevine (Vitis spp.). In order to set up the techniques for investigating downy mildew disease dynamics and genetic structure, co-dominant, neutral, highly reproducible and polymorphic microsatellite markers for P. viticola were developed. Five markers, two with a (TC)n repeat (loci BER and ISA), two with a (TC)n(AC)n repeat (loci CES and REX) and one with a (CT)n(CTAT)n repeat (locus GOB), were selected. Simple sequence repeat (SSR) markers revealed different degrees of polymorphism within 190 oil spots (disease symptoms) collected from an infected Italian vineyard. The most polymorphic SSR marker GOB showed 43 alleles (Nei's expected gene diversity He = 0.89) while CES, ISA, BER and REX showed 14 (He = 0.71), 4 (He = 0.57), 3 (He = 0.24) and 1 allele (He = 0), respectively. A high throughput DNA extraction method, that allowed molecular analysis of this obligate pathogen directly in the host without any isolation procedure, was developed. The quality and quantity of oil spots did not influence the SSR analysis. Amplified SSR loci were separated by electrophoresis on a Beckman–Coulter 2000XL sequencer and automatically analysed. The objective of this study was to develop molecular biological tools and methods that allow high throughput analysis of the downy mildew populations.
TL;DR: A remarkable increase in the activity of garlic extracts was observed when extracts were mixed with oil, and the treatment comprising 1% extract plus oil was as effective as the fungicide treatment in controlling both green and blue molds on Valencia oranges.
Abstract: Water and ethanol extracts of garlic cloves were applied to artificially inoculated citrus fruits to test their efficacy in the control of Penicillium digitatum and P. italicum, the cause of citrus green and blue mold respectively. Extracts were tested either alone, or in combination with vegetable (sunflower) cooking oil or fruit wax at the rate of (0.1% v/v), using two orange cultivars (Valencia and Shamouti), and grapefruit. Treated fruits were stored at 10 ± 1 ◦ C, and 90–95% relative humidity for 30 days. All concentrations of extracts were more effective than the water control in inhibiting the growth and development of both pathogens, but were not as effective as the fungicide treatment (imazalil 500 ppm + quazatine 1000 ppm). A remarkable increase in the activity of garlic extracts was observed when extracts were mixed with oil. Consequently, the treatment comprising 1% extract plus oil was as effective (100% control) as the fungicide treatment in controlling both green and blue molds on Valencia oranges.
TL;DR: A sensitive real-time polymerase chain reaction (PCR) assay was developed for the quantification of Spongospora subterranea, the cause of powdery scab and root galling in potato, and the vector of Potato mop top virus and was successful even at low inoculum levels.
Abstract: A sensitive real-time polymerase chain reaction (PCR) assay was developed for the quantification of Spongospora subterranea, the cause of powdery scab and root galling in potato, and the vector of Potato mop top virus. A specific primer pair and a fluorogenic TaqMan® probe were designed to perform a quantitative assay for the detection of S. subterranea in soil, water and plant tissue samples. The assay was tested using DNA from cystosori, zoospores, plasmodia and zoosporangia of the pathogen. DNA was extracted directly from cystosori suspended in water and from clay soil with varying levels of added cystosori. DNA obtained from zoospores released into nutrient solution by cystosori in the presence of tomato bait plants was also tested, as was DNA from plasmodia and zoosporangia in infected tomato roots. In many cases, detection was successful even at low inoculum levels. This specific quantitative assay could therefore be a useful tool for studying the biology of S. subterranea, and for the optimisation of disease avoidance and control measures.
TL;DR: Steaming at 50 or 60°C for 3min, followed by an 8-min resting period in the steamed soil and immediate removal from the soil thereafter, resulted in 100% kill of all weeds, diseases and nematodes.
Abstract: Agricultural soil samples containing survival structures of the fungal crop pathogens Verticillium dahliae, Sclerotinia sclerotiorum, Sclerotium cepivorum, Pythium ultimum, potato cyst nematodes Globodera rostochiensis and G. pallida and weeds Chenopodium album and Agropyron repens [Elymus repens] were treated in the laboratory with aerated steam at temperatures ranging from 40 to 80°C in a specially constructed apparatus. Steaming at 50 or 60°C for 3min, followed by an 8-min resting period in the steamed soil and immediate removal from the soil thereafter, resulted in 100% kill of all weeds, diseases and nematodes. When steamed at 45°C, there was a small but significant reduction in the survival of V. dahliae microsclerotia but no reduction in survival of S. cepivorum.
TL;DR: Results indicate that competition for nutrients is one of the modes of action of P. agglomerans CPA-2, but that physical contact between pathogen and antagonist is important for effective control.
Abstract: Pantoea agglomerans CPA-2 is an effective antagonist against the postharvest pathogens Penicillium digitatum and Penicillium italicum on citrus fruits but its mode of action is unknown. Possible mechanisms studied in this work were antibiosis, induced resistance, competition and production of chitinolytic enzymes. P. agglomerans CPA-2 was unable to produce antibiotics or chitinolytic enzymes under the conditions tested. Induction of resistance by P. agglomerans CPA-2 was studied in oranges by measuring phenylalanine ammonia lyase and peroxidase enzyme activity in the orange peel at different time points after inoculation with the antagonist and/or the pathogen. No significant augmentation of enzyme activity after inoculation of oranges with P. agglomerans CPA-2 in the presence or absence of the pathogen was observed. P. agglomerans was effective only when it is in close contact with the pathogens. Competition for nutrients was studied using tissue culture plates with cylinder inserts, which allowed competition for nutrients to be studied without competition for space since physical contact between pathogen and antagonist was avoided. The presence of P. agglomerans in the tissue culture wells clearly decreased the germination of Penicillium conidia present in the cylinder when diluted orange peel extract or diluted potato dextrose broth was the nutrient source. Germination of Penicillium conidia, however, was almost completely inhibited when pathogen and antagonist were in physical contact. These results indicate that competition for nutrients is one of the modes of action of P. agglomerans CPA-2, but that physical contact between pathogen and antagonist is important for effective control.
TL;DR: β-Aminobutyric acid (BABA), an inducer of pathogen resistance in plants, induced disease resistance in reproductive parts of the plant, such as grapefruit peel tissue, by application of BABA to specific wound sites on the fruit peel surface.
Abstract: β-Aminobutyric acid (BABA), an inducer of pathogen resistance in plants, induced disease resistance in reproductive parts of the plant, such as grapefruit peel tissue. Application of BABA to specific wound sites on the fruit peel surface induced resistance to Penicillium digitatum, the main postharvest pathogen of citrus fruit, in a concentration-dependent manner, being most effective at 20mM, and rather less effective at either higher or lower concentrations. The effect of BABA in inducing resistance to P. digitatum in the fruit peel surface was local and limited to the vicinity (within 1–2cm) of the BABA-treated site. In addition to inducing pathogen resistance, increasing concentrations of BABA (from 1 to 100mM) also exhibited direct antifungal activity and inhibited P. digitatum spore germination and germ tube elongation in vitro. The induction of resistance to P. digitatum by BABA was accompanied by the activation of various pathogen defense responses in grapefruit peel tissue, including activation of chitinase gene expression and protein accumulation after 48h, and an increase in phenylalanine ammonia lyase (PAL) activity after 72h.
TL;DR: Findings indicate the existence of Xcc strains in Tanzania that are distinct from those included in Biolog and MIS databases, and warrant continued improvement of databases and inclusion of pathogenicity testing, using universally susceptible cultivars, as an integral part of strain identification.
Abstract: Black rot, caused by Xanthomonas campestris pv. campestris (Xcc), is a major disease constraint to cabbage production by smallholder farmers in Africa. Variability exists within the pathogen, and yet differentiation of Xcc strains from other closely-related xanthomonads attacking crucifers is often difficult. The Biolog system, fatty acid methyl ester analysis using microbial identification system (MIS), rep-PCR and pathogenicity tests were used to identify and characterise Xcc strains from Tanzania. Great diversity was observed among Xcc strains in their Biolog and rep-PCR profiles. Specific rep-PCR genomic fingerprints were linked to some geographical areas in the country. Most of the Xcc strains were clustered in two groups based on their fatty acid profiles and symptom expression in cabbage although some deviant strains were found. Each of the methods allowed a degree of identification from species, pathovar to the strain level. Biolog and MIS identified all Xcc strains at least to the genus level. Additionally, Biolog identified 47% of Xcc strains to the pathovar and 43% to strain level, whereas MIS identified 43% of the strains to pathovar level. In the absence of a database, the utility of rep-PCR for routine diagnosis of strains was limited, although the procedure was good for delineation of Xcc to the strain level. These findings indicate the existence of Xcc strains in Tanzania that are distinct from those included in Biolog and MIS databases. The limitations noticed warrant continued improvement of databases and inclusion of pathogenicity testing, using universally susceptible cultivars, as an integral part of strain identification.
TL;DR: Application of the presently developed PCR method for the detection of Guignardia citricarpa will enable citrus producing as well as importing countries to prevent further spread of this harmful organism.
Abstract: Based on the ITS regions of the ribosomal DNA, specific primer sets were developed for the citrus pathogen Guignardia citricarpa and the common citrus endophyte, G. mangiferae, and tested for their specificity against 37 isolates of G. citricarpa, 29 isolates of G. mangiferae, 10 isolates of related species and other fungi found on citrus. The efficacy of the PCR-detection method for G. citricarpa was approximately 60–70% for lesions without pycnidia, and approximately 90% for lesions with pycnidia. A reliability of 99% can be reached by analysing multiple lesions per sample. An internal control was developed to monitor DNA samples for PCR inhibition; samples with PCR inhibition should be re-examined. Detection by PCR is more rapid than the current five-day incubation method prescribed by the European Union for diagnosis of black spot lesions lacking the diagnostic pycnidia. The latter method had an efficacy of 40–50%, while culturing of suspected lesions had an efficacy of 10%. Species-specific primers and ITS sequence data showed that G. citricarpa can occur as a symptomless endophyte in leaves. This shows that wild and cultivated plants occurring in citrus groves are potential carriers of this quarantine fungus. Application of the presently developed PCR method for the detection of G. citricarpa will enable citrus producing as well as importing countries to prevent further spread of this harmful organism.
TL;DR: A single application of prochloraz, tebuconazole, epoxiconazole or bromuconazoles, applied to durum wheat varieties at the manufacturer's recommended dose at the beginning of anthesis stage, provided good control of the disease when infective pressure in the field was low to medium, and when the main pathogens were F. graminearum and F. culmorum.
Abstract: In 1998–99 and 1999–2000 six trials were conducted to evaluate the effect of fungicides on Fusarium head blight in the field, on infected kernels and deoxynivalenol (DON) concentration in grain. A single application of prochloraz, tebuconazole, epoxiconazole or bromuconazole, applied to durum wheat varieties at the manufacturer's recommended dose at the beginning of anthesis stage, provided good control of the disease when infective pressure in the field was low to medium, and when the main pathogens were F. graminearum and F. culmorum. Kresoxim-methyl showed a low efficacy at controlling the disease. Tebuconazole, prochloraz and bromuconazole were effective at controlling F. graminearum and F. culmorum, while kresoxim-methyl was not effective in reducing Fusarium infected kernels. DON concentration in grain of cultivars inoculated with F. graminearum and F. culmorum was high, averaging 4.2 mg kg−1 (untreated control). Tebuconazole, prochloraz and bromuconazole reduced DON concentration by 43%, while epoxiconazole was ineffective. DON concentration in kernels of naturally infected cultivars was 1.95 mg kg−1, a concentration which exceeds the 1 mg kg−1 maximum level of contamination allowed in the United States. Furthermore prochloraz, bromuconazole and tebuconazole applications, in the naturally inoculated trials, reduced DON concentration from 73% to 96%, while epoxiconazole showed the lowest effectiveness. Moreover, a positive linear correlation between Fusarium infected grains and the DON concentration was observed.
TL;DR: Existing methods used to quantify microsclerotia of Verticillium dahliae in soil are reviewed, and some original results are presented to illustrate certain arguments.
Abstract: Existing methods used to quantify microsclerotia of Verticillium dahliae in soil are reviewed. Most quantification methods are soil-type dependent, but are useful for disease prediction within certain soils. The major factor determining the accuracy of dry plating methods is the amount of soil plated per Petri dish. Wet plating methods are less sensitive to higher amounts of soil, especially when the fraction smaller than 20 um is removed by wet sieving. Despite general assumptions, wet plating methods do not have lower detection limits than dry plating methods. Dry plating methods are less variable at higher inoculum levels, but more variable at low inoculum levels. Bioassays are helpful tools in answering specific research questions, but are not convenient for large scale use. Molecular quantification techniques are promising, because they are not hampered by antagonistic effects, but data on their disease predictive abilities are still largely lacking. Suggestions are given for a better comparison of techniques, and some original results are presented to illustrate certain arguments.
TL;DR: Based on both conserved and divergent nt regions in the CP and ORF5, oligonucleotide primers were designed for the simultaneous RT-PCR detection of all GVA isolates and for the specific detection of the most divergent virus variants represented here by mild isolates of the virus.
Abstract: Eight isolates of Grapevine virus A (GVA), which induced different symptoms in leaves of Nicotiana benthamiana, were recovered from various grapevines. The dsRNA patterns of two isolates, which consistently induced mild vein clearing (referred here as mild isolates of GVA) were similar, but different from those of other isolates of GVA. Analysis based on overall nucleotide (nt) sequence identity in the 3′ terminal part of the GVA genome, comprising part of ORF3 (putative movement protein, MP), entire ORF4 (capsid protein, CP), entire ORF5 and part of 3′ UTR, revealed that GVA isolates separate into three groups (I, II, III), sharing 91.0–99.8% nt sequence identity within groups and 78.0–89.3% nt sequence identity between groups. Mild isolates of the virus were group III and shared only 78.0–79.6% nt sequence identity with the other isolates. The comparison of predicted amino acid sequences for MP and CP revealed many amino acid alterations, revealing distinct local net charges of these proteins for mild isolates of the virus. Based on both conserved and divergent nt regions in the CP and ORF5, oligonucleotide primers were designed for the simultaneous RT-PCR detection of all GVA isolates and for the specific detection of the most divergent virus variants represented here by mild isolates of the virus.