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Blight
Kinds of Blight Terms modified by Blight Selected AbstractsOccurrence and Distribution of Microdochium and Fusarium Species Isolated from Durum Wheat in Northern Tunisia and Detection of Mycotoxins in Naturally Infested GrainJOURNAL OF PHYTOPATHOLOGY, Issue 9 2009Lobna Gargouri Kammoun Abstract An outbreak of Fusarium Head Blight of durum wheat occurred in 2004 being localized in sub-humid and higher semi-arid region of Northern Tunisia. A mycological survey carried out throughout these regions, revealed that 78% of the prospected fields were infested. Results of the morphological and molecular identification, showed that the most common species isolated from diseased wheat spikes was Microdochium nivale var. nivale (63.5%), followed by Fusarium culmorum (26%), F. pseudograminearum (9%) and F. avenaceum (1.5%). To evaluate mycotoxin content of naturally infected grain, the amounts of trichothecene mycotoxin deoxynivalenol (DON) in harvested grain from 45 fields were quantified by RIDASCREEN DON Enzyme Immunoassay Kit (ELISA). This study showed that the infection levels in freshly harvested grain were very low and the maximum deoxynivalenol (DON) level of the positive samples was 53 ppb. This is the first report on the natural occurrence of DON in naturally infected wheat grain sampled from Northern Tunisia. [source] Ultrastructural and Immunocytochemical Studies on Effects of Barley Yellow Dwarf Virus , Infection on Fusarium Head Blight, Caused by Fusarium graminearum, in Wheat PlantsJOURNAL OF PHYTOPATHOLOGY, Issue 1 2006Y. Liu Abstract The interactions between barley yellow dwarf virus (BYDV) and Fusarium head blight (FHB), caused by Fusarium graminearum, were studied in the two winter wheat cultivars (cvs.), Agent (susceptible to FHB) and Petrus (moderately resistant to FHB), using ultrastructural and immunocytochemical methods. Infections of wheat plants of both cvs. by BYDV increased susceptibility to FHB. BYDV infection caused numerous cytological changes in lemma tissue of both cvs. such as formation of vesicles in the cytoplasm, degradation of fine structures of chloroplasts of both cvs. and accumulation of large starch grains in the chloroplasts. Electron microscopical studies showed that the development of F. graminearum on spike surfaces was not affected in BYDV-infected plants. After penetration and intercellular growth in lemma tissue, defence responses to Fusarium infections were markedly reduced in BYDV-diseased plants compared to the tissue of virus-free plants. At sites of contact of fungal cells with host tissue, depositions of cell wall material were distinctly less pronounced than in tissues of virus-free plants of cv. Petrus. Detection of , -1,3-glucanases and chitinases in lemma tissue of cv. Agent revealed no appreciably increased accumulation of both defence enzymes in F. graminearum -infected virus-free and BYDV-infected tissues compared to the non-infected control tissue. On the other hand, in cv. Petrus, infection with F. graminearum induced a markedly enhanced activity of both enzymes 3 days after inoculation. The increase of both enzyme activities was less pronounced in BYDV-infected plants than in tissue exclusively infected with F. graminearum. Cytological studies suggest that in contrast to the susceptible cv. Agent postinfectional defence responses may play still an important role in the resistance of the moderately resistant cv. Petrus to FHB. [source] Use of a Mini-Dome Bioassay and Grafting to Study Resistance of Chickpea to Ascochyta BlightJOURNAL OF PHYTOPATHOLOGY, Issue 10 2005W. Chen Abstract A mini-dome bioassay was developed to study pathogenicity of Ascochyta rabiei and relative resistance of chickpea (Cicer arietanium). It was determined that the best condition for assaying pathogenicity of A. rabiei was to use 2 × 105 spores/ml as inoculum and to maintain a leaf wetness period of 24 h under mini-domes at a temperature between 16 and 22°C. This mini-dome pathogenicity assay was used to determine relative resistance of six chickpea cultivars (cvs) to isolates of two pathotypes of A. rabiei. Grafting was employed to detect any translocated factors produced in the chickpea plant that mediate disease response, which could help elucidate possible resistance mechanisms to Ascochyta blight. The six chickpea cv. were grafted in all possible scion,rootstock combinations, and then inoculated with isolates of two pathotypes of A. rabiei using the mini-dome technique. Results showed that self-grafted-resistant plants remained resistant and self-grafted-susceptible plants stayed susceptible, indicating the grafting procedure did not alter host response to infection by A. rabiei. Susceptible scions always exhibited high and similar levels of disease severity regardless of rootstock genotypes, and resistant scions always showed low and similar levels of disease severity when they were grafted onto any of the six rootstock genotypes. Orthogonal contrasts showed that scion genotypes determined disease phenotype, and that rootstock genotypes had no contribution to disease phenotype of the scions. The pathogenicity assay did not detect any translocated disease-mediating agents responsible for susceptibility or resistance in chickpea. Disease phenotypes of Ascochyta blight of chickpea were conditioned locally by scion genotypes. [source] Identification of Critical Stage for Disease Development and Biocontrol of Alternaria Blight of Indian Mustard (Brassica juncea)JOURNAL OF PHYTOPATHOLOGY, Issue 4 2004P. D. Meena Abstract Fungicides mancozeb and carbendazim caused 100% reduction in mycelial growth of Alternaria brassicae over control in vitro while 1% (w/v) aqueous bulb extract of Allium sativum and leaf extract of Acacia nilotica caused significant reductions. In dual culture, GR isolate of Trichoderma viride performed the best among the test isolates of Trichoderma, causing 81%, 82% reduction in mycelial growth of A. brassicae over control. Performance of isolates SI-2, P and SI-1 of T. viride were at par (P < 0.01) with that of GR isolate. Spraying of A. brassicae at different ages of the mustard host plant identified 75 days after sowing (d.a.s.) as the most critical age of the mustard plant for development of Alternaria blight severity on the crop with 45 d.a.s. being the next most important one. Mancozeb was the best among all the treatments, resulting in the lowest disease severity on leaves of mustard at both Sewar and Ludhavai as also the lowest A-value (area under disease progress curve). Performance of bulb extract of A. sativum in checking the disease severity on leaves and pods was at par (P,<,0.05) with mancozeb. The GR isolate of T. viride was at par with mancozeb in checking blight severity on mustard leaves at Sewar while performance of the bioagent was significantly (P,<,0.05) inferior to the chemical fungicide at Ludhavai. Performance of the bioagent isolate GR of T. viride in checking the disease severity on pods was at par (P < 0.05) with mancozeb at both Sewar and Ludhavai, the treatment recording the lowest A-value on pods. While application of bulb extract of A. sativum resulted in highest seed yield at Sewar in 2001,2002, the bioagent isolate GR of T. viride did so at Ludhavai, both the treatments being at par (P < 0.05) with mancozeb and significantly higher than control. Application of bulb extract of A. sativum at 45 and 75 d.a.s. resulted in lowest blight severity on leaves and pods as also in highest seed yield among the different single and combination of treatments. Although disease severity in the treatment was at par (P < 0.05) with that in mancozeb, application of the plant extract at the two stages of crop growth resulted in significantly higher seed yield compared with the two applications of the chemical fungicide. However, application of the treatments singly only at 75 d.a.s., GR isolate of T. viride at 45 and 75 d.a.s., A. sativum 45 d.a.s. + T. viride 75 d.a.s., and T. viride 45 d.a.s. + A. sativum 75 d.a.s. resulted in seed yield at par (P < 0.05) with application of bulb extract of A. sativum at 45 and 75 d.a.s. [source] Studies on Symptom Development, Phenolic Compounds and Morphological Defence Responses in Wheat Cultivars Differing in Resistance to Fusarium Head BlightJOURNAL OF PHYTOPATHOLOGY, Issue 4-5 2002E. SIRANIDOU Abstracts Development of Fusarium head blight, caused by Fusarium culmorum, was evaluated in seven winter wheat cultivars and one spring wheat cultivar in an outdoor pot experiment. Of the cultivars studied, only the spring wheat cultivar Frontana exhibited resistance against initial infection by the fungus. Significantly higher amounts of free phenolic compounds were found in the glumes, lemmas and paleas of Frontana prior to and at all sampling times after inoculation, in comparison to the winter wheat cultivar Agent. Furthermore, the amount of p -coumaric acid increased significantly in the glumes, lemmas and paleas of the cultivar Frontana 2 days after inoculation compared to that in uninoculated spike tissues. However, the amounts of ferulic acid between inoculated and healthy plant tissues did not differ. Ultrastructural studies indicated more pronounced structural defence responses, such as cell wall appositions, in the infected lemma tissue of the resistant cultivar Frontana compared with the susceptible Agent 3 days after inoculation. Immunogold labelling of lignin revealed no differences in the density of gold particles on the cell walls of healthy lemma tissue in the two cultivars. However, density of particles increased in the infected lemma tissue of the resistant cultivar Frontana on cell walls adjacent to the fungal cells, 3 days after inoculation. The susceptible cultivar Agent showed little or no response to the infection. Phenolic compounds appear to play a role in the resistance of the cultivar Frontana to F. culmorum. [source] Influences of Northern Leaf Blight on corn silage fermentation quality, nutritive value and feed intake by sheepANIMAL SCIENCE JOURNAL, Issue 4 2010Peng WANG ABSTRACT This study examined the differences between non-inoculated (control) corn and Northern Leaf Blight (NLB)-damaged corn (inoculated corn); dry matter (DM) yield, silage fermentation quality, nutritive value and feed intake by sheep were compared. Leaf, stem and grain dry weights and gross yield of inoculated corn were significantly (P < 0.05) decreased compared with control corn. The contents of water-soluble carbohydrate and nitrogen-free extract (NFE) were decreased in inoculated corn compared with control corn. Silage made from both inoculated and control corn showed good fermentation quality. The digestibility of DM, organic matter, ether extract, NFE, and energy of silage made from inoculated corn were significantly (P < 0.05) lower, and contents of total digestible nutrients (TDN) and digestible energy (DE) were also significantly (P < 0.05) lower compared with silage made from the control corn. DM intake showed no significant discrepancy between the two types of silage. TDN and DE intakes from inoculated silage were significantly (P < 0.05) lower compared with control silage. From the above results it was shown that NLB caused a decrease in DM yield and NFE content in corn and a decrease in the nutritive value and feed intake of silage. [source] 3-Methylarginine from Pseudomonas syringae pv. syringae 22d/93 Suppresses the Bacterial Blight Caused by Its Close Relative Pseudomonas syringae pv. glycineaCHEMBIOCHEM, Issue 12 2008Sascha D. Braun Abstract The epiphyte Pseudomonas syringae pv. syringae 22d/93 (Pss22d) produces a toxin that strongly inhibits the growth of its relative, the plant pathogen P. syringae pv. glycinea. The inhibition can be overcome by supplementing the growth medium with the essential amino acid, L -arginine; this suggests that the toxin acts as an inhibitor of the arginine biosynthesis. The highly polar toxin was purified by bioassay-guided fractionation using ion-exchange chromatography and subsequent RP-HPLC fractionation. The structure of the natural product was identified by HR-ESI-MS, HR-ESI-MS/MS, and NMR spectroscopy experiments as 3-methylarginine. This amino acid has previously only been known in nature as a constituent of the peptide lavendomycin from Streptomyces lavendulae. Results of experiments in which labeled methionine was fed to Pss22d indicated that the key step in the biosynthesis of 3-methylarginine is the introduction of the methyl group by a S -adenosylmethionine (SAM)-dependent methyltransferase. Transposon mutagenesis of Pss22d allowed the responsible SAM-dependent methyltransferase of the 3-methylarginine biosynthesis to be identified. [source] Passage through alternative hosts changes the fitness of Fusarium graminearum and Fusarium pseudograminearumENVIRONMENTAL MICROBIOLOGY, Issue 2 2007Olufemi A. Akinsanmi Summary Species of the necrotrophic fungal pathogen Fusarium that cause head blight and crown rot of cereals including wheat also infect a number of alternative host plants. This raises the prospect of more damaging pathogen strains originating and persisting as highly successful saprophytes on hosts other than wheat. The immediate impact on pathogenic (aggressiveness) and saprophytic (growth rate and fecundity) behaviour of six isolates with low, moderate or high initial aggressiveness was examined in two species of Fusarium after their passage through 10 alternative plant hosts. One passage through alternative hosts significantly reduced the pathogenic fitness of most isolates, but this change was not associated with a concomitant change in their overall saprophytic behaviour. The overall weak association between aggressiveness, fecundity and growth rate both before and after passage through the alternative hosts indicate that pathogenic and saprophytic fitness traits may be independently controlled in both Fusarium species. Thus, there was no trade-off between pathogenic and saprophytic fitness in these necrotrophic plant pathogens. [source] Prediction studies supported by computer on potato late blight in central Anatolia in Turkey,EPPO BULLETIN, Issue 2 2007E. Cakir Prediction of potato late blight epidemics, caused by Phytophthora infestans (Mont) de Bary, was studied in three different villages of Bolu Province having large potato growing areas with the Winstel and Ullrich Schrodter models in the years 2002,05. During these years, a late blight outbreak was observed only in 2005 with the disease being less apparent in the other years. The Ullrich Schrodter model was found to poorly predict potato late blight epidemics in 2005. The Winstel model gave first warnings too early but correctly predicted late infections. Both the A1 and A2 mating types were found in Central Anatolia for the first time, in Bolu province. [source] First laboratory confirmation of Xylophilus ampelinus in Slovenia,EPPO BULLETIN, Issue 1 2005T. Dreo Bacterial blight of grapevine is caused by a slow-growing bacterium Xylophilus ampelinus. It has been suspected to occur in Slovenia on the basis of visual observation of characteristic symptoms in the 1960s. In the present study, symptoms were recorded in an infected vineyard during three consecutive years (2002/2004). Samples from this vineyard were tested by nested-PCR and isolation of bacteria on media was attempted. In the first year, angular lesions on leaves were highly expressed and an isolate morphologically similar to X. ampelinus was obtained from one sample. It was purified and identified as X. ampelinus using biochemical and nutritional tests, fatty acid analysis, immuno-fluorescence, nested PCR and partial sequencing of the 16S rRNA gene. The 16S rDNA sequence showed 99,100% homology to known sequences of X. ampelinus strains, including the type strain. Pathogenicity of the isolate was confirmed in tissue-cultured and potted grapevine plants. In the following two years, symptoms of bacterial blight were only faintly expressed. Using isolation on media and nested-PCR, 23 and 17 extracts prepared from 10 and 8 grapevines, respectively, were analysed. In 2003, no positive sample was found, but X. ampelinus was again isolated and identified by colony morphology and nested-PCR in 2004. [source] Osmotic shock tolerance and membrane fluidity of cold-adapted Cryptococcus flavescens OH 182.9, previously reported as C. nodaensis, a biocontrol agent of Fusarium head blightFEMS YEAST RESEARCH, Issue 3 2007Christopher A. Dunlap Abstract Cryptococcus flavescens (previously reported as C. nodaensis), a biological control agent of Fusarium head blight, has been previously shown to have improved desiccation tolerance after cold adaptation. The goal of the current study was to determine the effect of cold adaptation on the physicochemical properties of C. flavescens that may be responsible for its improved desiccation tolerance. The results show that cold adaptation improves liquid hyperosmotic shock tolerance and alters the temperature dependence of osmotic shock tolerance. Fluorescence anisotropy was used to characterize differences in the membrane fluidity of C. flavescens with and without cold adaptation. Force curves from atomic force microscopy showed a significant increase in the cell wall spring constant after cold adaptation. Cold adaptation of C. flavescens during culturing was shown to produce smaller cells and produced a trend towards higher CFU yields. These results suggest that cold adaptation significantly alters the membrane properties of C. flavescens and may be an effective method of improving the desiccation tolerance of microorganisms. In addition, we provide information on the correct naming of the isolate as C. flavescens. [source] Characteristics of the Cryphonectria parasitica isolated from Quercus in SlovakiaFOREST PATHOLOGY, Issue 5 2010K. Adam, íková Summary The occurrence of chestnut blight (Cryphonectria parasitica) on oaks in mixed chestnut-oak forests was studied in 2003,2008 in Slovakia. Infections on living Quercus trees were found at four of seven localities. The disease incidence on oaks ranged from 1.3% to 15.8%. The symptoms on infected oaks were similar to those on chestnut, but less conspicuous. Cankers of C. parasitica were found only on Quercus robur and Q. petraea. A total of 22 isolates of C. parasitica, all virulent, were isolated. Each site yielded only a single vc type (EU12 or EU13). Field inoculation experiments on chestnuts with seven strains of C. parasitica from oaks and an isolate from Castanea sativa showed no differences in virulence. On Quercus robur stems, the cankered area was significantly smaller than on C. sativa and the cankers developed very slowly. [source] Distribution and severity of damage by Cryphonectria parasitica in the chestnut stands in Guilan province, IranFOREST PATHOLOGY, Issue 5 2010E. Ghezi Summary Chestnut blight caused by Cryphonectria parasitica has recently been reported from Guilan province, the only region with natural chestnut (Castanea sativa) stands in Iran. During the past few years, chestnut stands in Iran have been seriously threatened by the fungus, incidence of the disease is increasing and vast canopies are reduced to sprouts. As yet, there is no report on the disease distribution and severity in this region. Six sites from three main growing regions of chestnut in Guilan province were selected for investigation. We report occurrence and evaluation of the damage of the disease caused by C. parasitica. To evaluate the scale of damage, the investigated trees were classified into six categories based on the degree of crown damage, the number of canker wounds and the presence of the fungus. Index of health condition was calculated for all sites. During this study, a total of 250 isolates of Cryphonectria species were obtained, of which 232 isolates were C. parasitica and 18 were Cryphonectria radicalis. Castanea parasitica was observed in all regions. Index of health condition was scored from 0 to 6 with 0 being disease free and six being the most severe infection. Index results in the investigated sites varied between 0.69,5.45 and 0.93,5.55 for years 2006 and 2007, respectively. The highest damage was found in Doran (IH = 5.55), which is located some 100 km away from Shahbalutmahalleh, the site with lowest damage (IH = 0.93). This is the first extended report on aspects of chestnut blight in Iran. [source] Vegetative compatibility types of Cryphonectria parasitica, causal agent of chestnut blight, in the Black Sea region of TurkeyFOREST PATHOLOGY, Issue 6 2009S. Akilli Summary Vegetative compatibility types (vc types) of 296 isolates of the chestnut blight fungus, Cryphonectria parasitica, were determined. The isolates had been obtained from 32 localities in 11 provinces in the Black Sea region of Turkey. Five vc types were detected: EU-1, EU-12, EU-14, EU-2 and EU-5. The number of vc types found in single provinces varied between one and five. All of the five vc types were present only in the Kastamonu province. Vc type EU-1 was detected in all the provinces. EU-1 accounted for 90.8% of all isolates. Vc type EU-12 was present in eight provinces and accounted for 6.8% of the isolates, whereas one or two isolates each of EU-14, EU-2 and EU-5 were found in one or two provinces. Isolates possessing the white colony phenotype were considered to be hypovirulent. Hypovirulent isolates of each vc type were found, and they were detected in nine of 11 provinces. [source] Sirococcus shoot blight on Picea spinulosa in BhutanFOREST PATHOLOGY, Issue 1 2007T. Kirisits Summary During a recent survey of forest tree diseases in Western and Central Bhutan, Sirococcus shoot blight and an associated Sirococcus sp. were found on saplings and mature trees of Eastern Himalayan spruce (Picea spinulosa). Based on morphological characteristics and DNA sequence comparisons of the ITS region of the rDNA operon, representative isolates from Bhutan were unequivocally identified as Sirococcus conigenus. The DNA sequence data also showed that these isolates belong to the P group of S. conigenus. To our best knowledge, this is the first report of Sirococcus shoot blight from the Himalayas or any other part of Asia. Sirococcus conigenus does not appear to cause dramatic damage at the moment, but this fungus has the potential to cause severe disease problems on P. spinulosa in Bhutan. [source] Dothistroma (red-band) needle blight of pines and the dothistromin toxin: a reviewFOREST PATHOLOGY, Issue 3 2004R. E. Bradshaw Summary Dothistroma (red-band) needle blight has been a problem in plantations of exotic pines in the southern hemisphere for many decades. The prevalence of this disease is currently increasing in the northern hemisphere and is now affecting trees in their native ranges. The fungal pathogen Mycosphaerella pini with its anamorph Dothistroma pini, which is responsible for the disease, produces a toxin, dothistromin, that is closely related to the potent carcinogen, aflatoxin. Understandably this has provoked concern about possible effects on the health of forestry workers. This review gives a broad coverage of literature on both disease and toxin. The fungus has a complicated taxonomy with many synonyms and in most countries only the anamorph is found. It is a necrotrophic pathogen that kills needle tissue and completes its life cycle in the lesion thus formed. Dispersal of the disease is normally by rain splash of conidiospores but there is evidence that long range dispersal has occurred by transport of contaminated plant tissue and by wind/cloud dispersal of spores in air currents. The severity of disease is affected by humidity, temperature and light. There is variation in susceptibility of different Pinus species and some achieve increased resistance with age. The current method of control in southern hemisphere plantation forests is through spraying with copper fungicides and, with P. radiata, increased disease resistance has been achieved through a breeding programme. The dothistromin toxin is a difuroanthraquinone and is similar in structure to the aflatoxin precursor versicolorin B. Part of a gene cluster encoding dothistromin biosynthetic genes has been cloned and this has confirmed parallels between the dothistromin and aflatoxin biosynthetic pathways. Dothistromin produces damaging oxygen radicals by reductive oxygen activation rather than by photosensitization, but is also thought to exert its toxic effects on specific cellular targets. Studies have shown that dothistromin is a weak mutagen and clastogen and is therefore a potential carcinogen. Although the risks to forest workers are considered very low it is prudent to avoid unnecessary exposure during periods when dothistromin levels are likely to be at their peak. Résumé La maladie des bandes rouges causée par Dothistroma est un problème dans les plantations de pins exotiques de l'hémisphère sud depuis de nombreuses années. La prévalence de cette maladie est en augmentation dans l'hémisphère nord et affecte maintenant les pins dans leurs régions d'origine. Le champignon pathogène Dothistroma pini, responsable de la maladie, produit une toxine, la dothistromine, proche de l'aflatoxine qui est un puissant carcinogène. Ceci pose donc la question des effets possibles sur la santé des travailleurs forestiers. Cette revue repose sur une large couverture de la littérature concernant aussi bien la maladie que la toxine. Le champignon a une taxonomie complexe avec de nombreux synonymes, et seul l'anamorphe se rencontre dans de nombreux pays. C'est un champignon nécrotrophe qui tue les tissus de l'aiguille et réalise son cycle biologique dans la lésion ainsi formée. La dissémination de la maladie s'effectue principalement par éclaboussures de pluie contenant les conidies mais une dissémination à longue distance a été mise en évidence par transport de matériel contaminé ou par dissémination des spores par le vent ou les nuages dans les courants aériens. La sévérité de la maladie est affectée par l'humidité, la température et la lumière. Il existe des différences de sensibilité entre espèces de Pinus, et certaines présentent une résistance accrue avec l'âge. La méthode actuelle de lutte dans les forêts de plantations de l'hémisphère sud consiste à pulvériser des fongicides à base de cuivre ; dans le cas de Pinus radiata, une augmentation de la résistance a été obtenue grâce à un programme d'amélioration génétique. La toxine dothistromine est une difuroanthraquinone, similaire en structure à la versicolorine B, précurseur de l'aflatoxine. Une partie d'une batterie de gènes comprenant des gènes de biosynthèse de la dothistromine a été clonée, confirmant les analogies entre les voies de biosynthèse de la dothistromine et de l'aflatoxine. La dothistromine produit des radicaux oxygène nocifs par activation de la réduction de l'oxygène plutôt que par photosensibilisation, mais ses effets toxiques s'exercent aussi probablement sur des sites cellulaires spécifiques. Des études montrent que la dothistromine est un mutagène et clastogène faible, et donc potentiellement carcinogène. Bien que les risques pour les ouvriers forestiers soient considérés comme très faibles, il est prudent d'éviter dans la mesure du possible de s'exposer dans les périodes où les niveaux de dothistromine sont supposés élevés. Zusammenfassung Die Dothistroma -Nadelbräune ist in der Südhemisphäre in Plantagen mit exotischen Kiefernarten seit vielen Jahren ein Problem. In der Nordhemisphäre nimmt die Bedeutung dieser Krankheit derzeit zu und sie befällt nun Bäume auch in ihren natürlichen Verbreitungsgebieten. Der Erreger ist der Ascomycet Mycosphaerella pini (Anamorphe: Dothistroma pini). Der Pilz bildet das Toxin Dothistromin, das eng mit dem hochtoxischen Karzinogen Aflatoxin verwandt ist. Daraus ergab sich die Frage nach möglichen Nebenwirkungen dieser Baumkrankheit auf die Gesundheit von Waldarbeitern. Dieser Review fasst die Information über die Krankheit und das Toxin zusammen. Der Pilz hat eine komplizierte Taxonomie mit vielen Synonymen und in den meisten Ländern wurde nur die Anamorphe nachgewiesen. Er ist ein nekrotrophes Pathogen, das Blattgewebe abtötet, und in den so gebildeten Läsionen seinen Lebenszyklus abschliesst. Der normale Ausbreitungsweg der Krankheit erfolgt über Konidiosporen mit Regentropfen, aber es gibt auch Hinweise auf einen Ferntransport mit infiziertem Pflanzenmaterial und über die Verbreitung von Sporen mit dem Wind bzw. Wolken in Luftströmungen. Die Krankheitsintensität wird durch Luftfeuchte, Temperatur und Licht beeinflusst. Es gibt Unterschiede in der Anfälligkeit zwischen verschiedenen Kiefernarten und manche davon werden mit zunehmendem Alter resistenter. Derzeit werden in Plantagen der südlichen Hemisphäre Kupferfungizide zur Kontrolle dieser Krankheit eingesetzt und für Pinus radiata wurde in Züchtungsprogrammen eine erhöhte Resistenz erreicht. Das Toxin Dothistromin ist ein Difuroanthrachinon und ähnelt in seiner Struktur dem Aflatoxin-Präkursor Versicolorin B. Ein Teil des Genclusters, das die Dothistromin-Biosynthese codiert, wurde geklont, und es wurden dabei Parallelen zwischen dem Dothistromin- und dem Aflatoxin-Biosyntheseweg bestätigt. Dothistromin bildet schädliche Sauerstoffradikale (wahrscheinlich eher durch reduktive Sauerstoffaktivierung als durch Photosensibilisierung), es dürfte aber auch auf spezifische Zellkomponenten toxisch wirken. Dothistromin zeigt schwache mutagene und chromosomenschädigende Wirkungen und ist deshalb ein potentielles Karzinogen. Obwohl das Risiko für Waldarbeiter als gering eingeschätzt wird, sollte man in Perioden, in denen der Dothistromingehalt hoch sein dürfte, eine unnötige Exposition vermeiden. [source] Seasonal effect on infection and development of lesions caused by Cryphonectria parasitica in Castanea sativaFOREST PATHOLOGY, Issue 4 2003L. Guérin Summary Seasonal variation in the development of chestnut blight, caused by Cryphonectria parasitica, was investigated by inoculating in situ chestnut trees and in vitro excised chestnut segments, at either monthly or 3-monthly intervals throughout 30 months. Inoculations were made with conidia and mycelium of a virulent isolate and with mycelium of a hypovirulent isolate. Conidial inoculations of living sprouts or excised segments between May and July resulted in the greatest incidence of infection whereas inoculations in autumn and winter, in vitro as well as in situ, did not reveal any visible disease. However, from these symptomless inoculated stems, C. parasitica was isolated 3 months after inoculation. Inoculations with the mycelium of the virulent isolate always resulted in lesions, except in January 1999, and the greatest rate of lesion development occurred for inoculations made in the spring and summer. There was a significant seasonal effect on lesion development. Lesions caused by the hypovirulent isolate, smaller than those caused by the virulent isolate, followed a similar seasonal pattern. The same seasonal variations were observed for inoculations in vitro of excised segments. Relative water content (RWC) of chestnut bark significantly varied with bark sampling date. The rate of lesion development in sprouts significantly correlated with average minimum (ATn) and maximum (ATx) temperatures and the sum of rainfall during inoculation period, with the rate of lesion development measured in excised segments 10 days after inoculation (R10d) and with RWC measured on the day of inoculation. In multiple regression models, variables ATx and R10d best explained variation in lesion development. Résumé La variation saisonnière du développement de la maladie du chancre causée par Cryphonectria parasitica a étéétudiée en réalisant, une fois par mois ou par trimestre pendant deux ans et demi, des inoculations de châtaigniers in situ et des inoculations in vitro de branches coupées. Les inoculations ont été réalisées avec des conidies et du mycélium d'un isolat virulent et avec du mycélium d'un isolat hypovirulent. En Mai et Juin, les inoculations conidiennes ont provoqué le taux d'infection le plus élevé, in situ et in vitro. A l'inverse, en automne et en hiver, ces inoculations n'ont pas causé de symptômes. Cependant C. parasitica a été réisolé 3 mois plus tard, sur ces tiges ne présentant aucune lésion. Les inoculations avec du mycélium ont toujours résulté en des lésions, excepté en Janvier 1999, et le développement des lésions (R1m) a été le plus rapide au printemps et en été. La date d'inoculation a eu un effet significatif sur l'extension des lésions. Le même effet saisonnier était observé sur le développement des lésions causées par l'isolat hypovirulent, plus petites que celles causées par l'isolat virulent. Les mêmes variations saisonnières de l'extension des lésions étaient observées in vitro sur tiges excisées. Un effet saisonnier significatif a été mis en évidence sur la teneur en eau relative des écorces de châtaignier (RWC). Le développement des lésions dans les tissus vivants était significativement corrélé avec les températures moyennes minimale (ATn) et maximale (ATx) et la somme des précipitations (SR) calculées sur chaque période d'incubation, avec le développement des lésions in vitro (R10d) et avec RWC. La variation saisonnière du développement des lésions était le mieux expliquée, par un modèle de régression multiple, par ATx et R10d pour l'isolat virulent, et par ATx pour l'isolat hypovirulent. Zusammenfassung Der jahreszeitlich bedingte Einfluß auf die Entstehung von Kastanienrindenkrebs, verursacht von Cryphonectria parasitica, wurde durch Inokulation von Kastanienbäumen in situ und durch Beimpfung von geschnittenen Triebsegmenten in vitro in monatlichen oder drei-monatlichen Intervallen über dreißig Monate untersucht. Zur Inokulation wurden Myzel und Konidien eines virulenten Isolates und Myzel eines hypovirulenten Isolates verwendet. Mit Konidien wurde zwischen Mai und Juni die größte Infektionshäufigkeit auf lebenden Sprossen oder Triebsegmenten erreicht, während Inokulationen im Herbst und Winter keine sichtbaren Symptome hervorriefen. Jedoch konnte C. parastica drei Monate nach Inokulation von lebenden Sprossen isoliert werden, auch wenn keine Läsion sichtbar war. Außer im Januar 1999 führte Inokulation mit Myzel des virulenten Isolates immer zu Läsionen. Am häufigsten traten Läsionen bei Inokulationen im Frühling und im Sommer auf. Der Einfluß des Inokulationszeitpunktes auf die Ausbildung von Läsionen war signifikant. Inokulationen mit dem hypovirulenten Isolat zeigten eine ähnliche jahreszeitliche Schwankung wie jene mit dem virulenten Isolat, führten aber zu kleineren Läsionen. Die gleichen jahreszeitlichen Variationen wurden bei in vitro Inokulation von Kastanientrieben beobachtet. Der relative Wassergehalt (RWC) der Borke variierte signifikant mit dem Beprobungszeitpunkt der Borke. Die Bildung von Läsionen an lebenden Sprossen korrelierte signifikant mit den durchschnittlichen Temperaturminima (ATn) und -maxima (ATx), mit der Gesamtregenmenge (SR) während der Inokulationsperiode, mit der Bildung von Läsionen an Triebsegmenten (R10d) und mit dem am Inokulationstag gemessenen RWC. In einem multiplen Regressionsanalysenmodell zeigte sich, dass die jahreszeitliche Schwankung der Ausbildung von Kastanienrindenkrebs beim virulenten Isolat am besten durch die Variablen ATx und R10d, beim hypovirulenen Isolat durch ATx erklärt wurde. [source] Association of Sphaeropsis sapinea with insect-damaged red pine shoots and conesFOREST PATHOLOGY, Issue 1 2003E. Feci Summary The association of the shoot blight and canker pathogen Sphaeropsis sapinea with red pine (Pinus resinosa) shoots and cones damaged by insects (especially Dioryctria sp.) was investigated. Samples from a single plantation approximately 35 years old, in Sauk Co., Wisconsin and also from three plantations, between approximately 40 and 50 years old, located in an area of pine shoot moth activity in the preceding year in Adams Co., Wisconsin were visually examined. Samples were arbitrarily collected from trees felled in the first plantation in May. Pycnidia of S. sapinea and insect damage were observed on 56 of 91 (62%) of closed cones and 17 of 165 (7%) of previous year's shoots. In the absence of insect damage, pycnidia of the pathogen were identified only on eight of 91 (9%) closed cones and never on previous year's shoots. In each of the other three plantations, 10 trees were located at intervals along transects in mid-June; one branch from the lower half of the crown per tree was pruned off, and both current and previous year's shoots were examined. Insect damage and S. sapinea pycnidia were too rare on current year's shoots to draw any conclusions. Insect damage occurred on 20,40% of over 2000 previous year's shoots that were examined, but pycnidia of the pathogen were identified on only about 5%. Although infrequent, S. sapinea was identified in association with insect-damaged previous year's shoots from these three plantations three times more frequently than those without insect damage. Random amplified polymorphic DNA (RAPD) markers from eight randomly selected isolates were consistent with the A group of S. sapinea, which can be aggressive on red pine. This ability to exploit insect-damaged shoots may facilitate long-term persistence of S. sapinea at low disease incidence and severity. The potential role of insect wounds as infection courts and insects as vectors of this important pathogen of pines deserves further study. Résumé L'étude a porté sur l'association entre le parasite de pousses et agent de chancre Sphaeropsis sapinea, et les pousses et cônes de Pinus resinosa endommagés par des insectes (surtout Dioryctria sp.). Des échantillons ont été examinés visuellement; ils provenaient d'une plantation d'environ 35 ans à Sauk Co., Wisconsin, et de trois plantations âgées d'environ 40 et 50 ans situées dans une zone où les insectes des pousses avaient été actifs l'année précédente à Adams Co., Wisconsin. Dans la première plantation, les échantillons ont été prélevés arbitrairement sur des arbres abattus en mai. Des pycnides de S. sapinea et des dégâts d'insectes ont été observés sur 56/91 (62%) des cônes fermés et sur 17/165 (7%) des pousses de l'année précédente. En l'absence de dégâts d'insectes, les pycnides n'ont été trouvées que sur 8/91 (9%) des cônes fermés, et jamais sur les pousses de l'année précédente. Dans chacune des trois autres plantations, 10 arbres ont été choisis à la mi-juin le long de transects ; sur chaque arbre une branche a été coupée dans la moitié inférieure de la couronne, et les pousses de l'année en cours et de l'année précédente ont été examinées. Sur les pousses de l'année, les dégâts d'insectes et les pycnides de S. sapineaétaient trop rares pour pouvoir en tirer des conclusions. Parmi plus de 2000 pousses de l'année précédente examinées, les dégâts d'insectes étaient présents sur 20,40% des pousses, mais les pycnides n'ont été trouvées que sur environ 5% d'entre elles. Bien que peu fréquent chez ces trois plantations, S. sapinea a été trouvé associé aux pousses de l'année précédente, 3 fois plus fréquemment chez celles endommagées par les insectes que chez les non endommagées. Pour huit isolats pris au hasard, les marqueurs RAPD ont indiqué leur appartenance au groupe A de S. sapinea qui peut être agressif sur P. resinosa. Cette aptitude de S. sapineaà utiliser les pousses endommagées par les insects peut faciliter sa persistance à long terme à des niveaux bas d'abondance et de dégâts. Le rôle potentiel des blessures d'insectes comme voies d'infection, et des insectes comme vecteurs du champignon parasite mérite d'être étudié. Zusammenfassung Es wurde die Assoziation zwischen Sphaeropsis sapinea (Erreger von Triebsterben und Rindennekrosen) und Schädigung an Trieben und Zapfen von Pinus resinosa untersucht, durch Insekten (vorwiegend Dioryctria sp.) untersucht. Proben von einer ca. 35 Jahre alten Plantage in Sauk Co., Wisconsin und von drei 40-50jährigen Plantagen mit Dioryctria -Befall im Vorjahr in Adams Co., Wisconsin wurden makroskopisch untersucht. Die Proben am ersten Standort wurden von Bäumen entnommen, die im Mai gefällt wurden (willkürliche Auswahl). Pyknidien und Schädigung durch Insekten wurden an 56/91 (62%) der geschlossenen Zapfen und an 17/165 (7%) der vorjährigen Triebe beobachtet. An Organen ohne Schädigung durch Insekten wurden die Pyknidien des Pathogens nur bei 8/91 (9%) der geschlossenen Zapfen und in keinem Fall an den vorjährigen Trieben nachgewiesen. In den anderen drei Plantagen wurden Mitte Juni je 10 Bäume entlang von Transekten untersucht; pro Baum wurde aus dem unteren Kronenbereich ein Ast abgeschnitten und sowohl die diesjährigen als auch die vorjährigen Triebe wurden untersucht. An den diesjährigen Triebabschnitten waren sowohl Schädigungen durch Insekten als auch Pyknidien von S. sapinea zu selten, um daraus Schlüsse zu ziehen. An den vorjährigen Triebabschnitten kamen Insektenschäden an 20,40% von über 2,000 untersuchten Objekten vor, aber Pyknidien des Pathogens wurden nur in 5% der Fälle nachgewiesen. Trotz des geringen Vorkommens wurde S. sapinea auf den vorjährigen und von Insekten beschädigten Trieben dreimal häufiger nachgewiesen als an Trieben ohne Beschädigung. Acht zufällig ausgewählte Isolate wurden anhand von RAPD Markern der Gruppe A von S. sapinea zugeordnet, die auf P. resinosa agressiv sein kann. Die Fähigkeit von S. sapinea, durch Insekten beschädigte Triebe zu nutzen, kann das Überdauern des Pilzes auf einem niedrigen Befallsniveau erleichtern. Die Bedeutung von Wunden, die durch Insekten verursacht werden, als Infektionspforten und die mögliche Rolle von Insekten als Vektoren dieses wichigen Pathogens sollte in weiteren Untersuchungen geklärt werden. [source] Persistence of Cryphonectria hypoviruses after their release for biological control of chestnut blight in West Virginia forestsFOREST PATHOLOGY, Issue 6 2002Y.-C. Liu Summary Although Cryphonectria hypoviruses have been relatively successful as biological control agents of chestnut blight in Europe, their success in North America has been limited. Experimental releases of hypoviruses were made in 1978,82 at two sites in West Virginia forests with high densities of regenerating chestnut trees. Cryphonectria hypovirus 1 (CHV-1) from Europe, as well as American isolates of Cryphonectria parasitica containing CHV-3, were used for these releases. Although most trees died during the 5-year release period, it was not known if the hypoviruses persisted in the C. parasitica population at the two sites. When the experimental plots were revisited in 1994, few chestnut trees were found. The exception was one plot containing coppice sprouts that had grown from the root collars of the original trees. The authors intensively sampled C. parasitica from experimental plots and screened recovered isolates for double-stranded RNA (dsRNA). None of the isolates contained CHV-1; only six isolates contained CHV-3, all from the plots with the coppice sprouts. CHV-4, which occurs naturally in West Virginia forests and in two released isolates, hybridized to dsRNA from the isolates containing CHV-3, indicating mixed infections. CHV-4 also hybridized to dsRNA from other isolates sampled inside and outside the treated plots. In contrast to CHV-1 and CHV-3, however, CHV-4 has little effect on the growth or phenotype of C. parasitica. The limited persistence of CHV-1 and CHV-3 may have resulted when the C. parasitica population was reduced in size due to the failure of chestnut trees to resprout because of competition from other hardwood species. Résumé Bien que les hypovirus de Cryphonectria aient remporté un réel succès comme agents de lutte biologique contre le chancre du châtaignier en Europe, leur succès en Amérique du nord a été limité. Des applications d'hypovirus ont été faites en 1978,1982 en Virginie de l'ouest dans deux sites forestiers à fortes densités de régénérations de châtaigniers. Le CHV-1 originaire d'Europe ainsi que des isolats américains contenant le CHV-3 ont été utilisés dans ces essais. Bien que la plupart des arbres soient morts pendant les cinq ans de l'application, on ne sait pas si les hypovirus ont persisté dans la population de Cryphonectria parasitica. Quand les parcelles expérimentales ont été revisitées en 1994, peu de châtaigniers ont été trouvés. Un site faisait exception qui était un taillis de rejets issu de racines de souches. Nous avons échantillonné intensivement le C. parasitica dans les placettes et le dsRNA a été examiné dans les isolats obtenus. Parmi tous les isolats provenant des placettes de taillis, aucun ne contenait CHV-1 et seulement six contenaient CHV-3. CHV-4 qui existe naturellement dans les forêts en Virginie de l'ouest et dans deux des isolats appliqués, s'hybridait avec le dsRNA d'autres isolats contenant CHV-3, ce qui indique des infections mixtes. CHV-4 s'hybridait aussi avec le dsRNA d'autres isolats recueillis dans ou au dehors des placettes traitées. Contrairement à CHV1 et à CHV-3, CHV-4 a cependant peu d'effet sur la croissance et le phénotype de C. parasitica. La persistance limitée de CHV-1 et de CHV-3 peut avoir résulté de la réduction de la population de C. parasitica par un manque de rejets de châtaigniers dûà la compétition avec les autres espèces de feuillus. Zusammenfassung Währenddem der Einsatz von Cryphonectria Hypoviren zur biologischen Bekämpfung des Kastanienrindenkrebses in Europa relativ erfolgreich war, stimmt dies in Nordamerika nur begrenzt. In West-Virginia wurden in den Jahren 1978,82 Hypoviren in Experimenten an zwei Waldstandorten mit hoher Dichte regenerierender Edelkastanien freigesetzt. Cryphonectria hypovirus 1 (CHV-1) von Europa und amerikanische Isolate von Cryphonectria parasitica, die CHV-3 enthielten, wurden für diese Freisetzungsversuche verwendet. Obschon die meisten Bäume während der fünfjährigen Freisetzungsperiode abstarben, war unklar, ob die Hypoviren in der C. parasitica Population überlebten. Als die Versuchsflächen im Jahre 1994 erneut aufgesucht wurden, konnten nur noch wenige Edelkastanien gefunden werden mit Ausnahme einer Fläche, auf der die Wurzelanläufe ursprünglicher Bäume Stockausschläge trugen. Zahlreiche C. parasitica Stämme wurden von den Versuchsflächen gewonnen und auf Besiedlung mit dsRNA untersucht. Keines der Isolate enthielt CHV-1; nur sechs Isolate, welche alle von der Fläche mit den Stockausschlägen stammten, enthielten CHV-3. CHV-4, das natürlich in den Wäldern West-Viriginias vorkommt und in zwei der freigesetzten Isolate vorhanden war, hybridisierte mit dsRNA aus den Isolaten, die CHV-3 enthielten, was auf eine Mischinfektion hindeutet. CHV-4 hybridisierte auch mit dsRNA aus anderen Isolaten, die innerhalb und ausserhalb der behandelten Versuchsflächen gesammelt wurden. Im Gegensatz zu CHV-1 und CHV-3 war der Einfluss von CHV-4 auf den Phänotyp von C. parasitica gering. Die begrenzte Persistenz von CHV-1 und CHV-3 wird möglicherweise durch die Abnahme der C. parasitica Population als Folge des Ausbleibens der Regeneration der Edelkastanie bedingt. Erschwerend für die Edelkastanien dürfte sich zudem die Konkurrenz mit anderen Laubhölzern auswirken. [source] The impact of Sirococcus shoot blight on radial and height growth of Norway spruce (Picea abies) in young plantationsFOREST PATHOLOGY, Issue 3 2000E. Halmschlager Summary The impact of Sirococcus shoot blight on the radial and height growth of Norway spruce in a young plantation (approximately 20 years old) was investigated by examining the increment losses for four infection intensities (classes). The average diameter at breast height of trees in the lightly damaged class was 72% when compared with the average diameter of the healthy trees, whereas moderately and severely damaged tree classes were 67 and 57%, respectively. Using tree ring analysis, the development of radial growth over time due to intensity of infection was studied. Height growth of affected trees was also significantly reduced (up to 43%) compared with the healthy trees, thus indicating a dramatic impact of Sirococcus conigenus on the growth of young Norway spruce. [source] Is there a trade-off between aggressiveness and overwinter survival in Phytophthora infestans?FUNCTIONAL ECOLOGY, Issue 3 2007J. MONTARRY Summary 1Selection during interepidemic stages is crucial for the evolution of pathogen populations. Trade-offs involving aggressiveness (quantitative pathogenicity) have rarely been explored in pathogens with a life cycle requiring the disease-causing organism to change organs within the same host. 2We investigated the existence of a trade-off between aggressiveness and survival in Phytophthora infestans, the pathogen causing potato late blight. In France, P. infestans behaves as an obligate biotroph, surviving in infected tubers. Aggressive isolates, which are favoured during the epidemic, may exhaust their nutrient supply too quickly to bridge seasons, resulting in a possible trade-off between the two life stages. 3We inoculated tubers with isolates possessing different aggressiveness levels, let them overwinter as outdoor piles at three different sites, and scored the proportion of live tubers the following spring. 4At two sites, infection caused early tuber sprouting, which can be seen either as a manipulation of the host by the pathogen, or as an attempt by the host to escape. 5Overwinter survival was higher for control than for inoculated tubers, but did not differ between tubers inoculated with different isolates. This suggests that aggressiveness should gradually increase in P. infestans populations, unless a trade-off occurs at another stage of the life cycle. [source] Serological detection and immunogold localization of cross-reactive antigens shared by Camellia sinensis and Exobasidium vexansJOURNAL OF APPLIED MICROBIOLOGY, Issue 5 2007B.N. Chakraborty Abstract Aims:, Pathogenicity of Exobasidium vexans, causal agent of blister blight of tea, was studied in 30 commercially cultivated tea varieties by analysing the antigenic patterns of host and pathogen using immunological techniques. Methods and Results:, Whole plant inoculation of tea varieties with E. vexans showed that T-78 and T-17/1/54 were most susceptible and most resistant respectively. Antigen preparations from tea varieties, pathogen, nonpathogen (Fusarium oxysporum) and of nonhosts (Glycine max, Leucaena leucocephala and Oryza sativa) were compared by indirect enzyme-linked immunosorbent assay and dot-immunobinding assay using polyclonal antibodies raised against the pathogen, nonpathogen, susceptible and resistant tea varieties. Cross-reactive antigens (CRA) were found among susceptible varieties and E. vexans isolates but not in resistant varieties, nonhosts or nonpathogen. Indirect staining of antibodies using fluorescein isothiocyanate indicated CRA were concentrated mainly around epidermal and mesophyll cells in compatible host (T-78). This was substantiated by ultrastructural studies using gold-labelled antibodies through transmission electron microscopy which showed specific localization in the chloroplasts and host cytoplasm. Conclusion:, Pathogenicity of E. vexans to different tea varieties is therefore related to the level of antigenic similarity between host and pathogen. Significance and Impact of the Study:, Immunological methods proved to be valuable in screening commercially cultivated tea varieties against E. vexans. [source] Genetic characterization of Erwinia amylovora strains by amplified fragment length polymorphismJOURNAL OF APPLIED MICROBIOLOGY, Issue 2 2004A. Rico Abstract Aims:,Erwinia amylovora is one of the most important pathogens of pear and apple and is subject to strict quarantine regulations worldwide, although its patterns of dispersal are largely unknown. Previous attempts to fingerprint E. amylovora strains by molecular techniques have detected very little polymorphism because of the high genetic homogeneity of this bacterium. Our aim was to establish and test a typing method to quantify genetic diversity among strains of this plant pathogen. Methods and Results:, Twenty-two strains from different hosts and geographical locations were examined by PCR fingerprinting with four primers and by amplified fragment length polymorphism (AFLP) with four selected combinations of primers with a single base extension. PCR fingerprinting revealed little polymorphism producing the same amplification patterns for 17 strains, while the combined AFLP patterns yielded 78 polymorphic bands (34% of total bands) and allowed the differentiation of all but two strains. Clustering of strains in the resulting dendrogram was not correlated with host, year or country of isolation, and questions previous genealogies based on PFGE patterns. Conclusions:, The AFLP technique allowed the detection of an unprecedented number of genetic markers in E. amylovora and proved to be the most useful tool so far for discriminating among strains of this pathogen. The results obtained in this study strongly suggest the occurrence of multiple introductions of the pathogen in Spain and other European countries. Significance and Impact of the Study:, A major limitation in understanding the ecology of fire blight is the lack of typing techniques with a high power of discrimination. This study demonstrates the high resolution and the usefulness of the AFLP technique to differentiate among E. amylovora strains. [source] Status of Streptomycin Resistance Development in Xanthomonas oryzae pv. oryzae and Xanthomonas oryzae pv. oryzicola in China and their Resistance CharactersJOURNAL OF PHYTOPATHOLOGY, Issue 9 2010Ying Xu Abstract Rice leaves with bacterial blight or bacterial leaf streak symptoms were collected in southern China in 2007 and 2008. Five hundred and thirty-four single-colony isolates of Xanthomonas oryzae pv. oryzae and 827 single-colony isolates of Xanthomonas oryzae pv. oryzicola were obtained and tested on plates for sensitivity to streptomycin. Four strains (0.75%) of X. oryzae pv. oryzae isolated from the same county of Province Yunnan were resistant to streptomycin, and the resistance factor (the ratio of the mean median effective concentration inhibiting growth of resistant isolates to that of sensitive isolates) was approximately 226. The resistant isolate also showed streptomycin resistance in vivo. In addition to resistant isolates, isolates of less sensitivity were also present in the population of X. oryzae pv. oryzae from Province Yunnan. However, no isolates with decreased streptomycin-sensitivity were obtained from the population of X. oryzae pv. oryzicola. Mutations in the rpsL (encoding S12 protein) and rrs genes (encoding 16S rRNA) and the presence of the strA gene accounting for streptomycin resistance in other phytopathogens or animal and human pathogenic bacteria were examined on sensitive and resistant strains of X. oryzae pv. oryzae by polymerase chain reaction amplification and sequencing. Neither the presence of the strA gene nor mutations in the rpsL or rrs were found, suggesting that different resistance mechanisms are involved in the resistant isolates of X. oryzae pv. oryzae. [source] Silicon Suppresses Phytophthora Blight Development on Bell PepperJOURNAL OF PHYTOPATHOLOGY, Issue 7-8 2010Ronald D. French-Monar Abstract The application of silicon (Si) reduces the intensity of diseases in several economically important crops. This study aimed at determining the potential of this element to decrease the symptoms of Phytophthora blight development on bell pepper, caused by Phytophthora capsici. Bell pepper plants (Sakata Hybrid X pp6115) were initially grown in plastic pots with substrate composed of 1 : 1 mixture of sterile fine sand and Fafard No. 2 peat mix amended with calcium silicate (+Si) or calcium carbonate (,Si). Six weeks later, plants were transplanted to new pots that contained the same +Si and ,Si substrate but were infested with finely ground wheat grains (1- to 2-mm diameter) colonized by two isolates of P. capsici, Cp30 (compatibility type A1) and Cp32 (compatibility type A2). At the end of the experiment, roots and stems from plants of each treatment were collected to determine Si concentration. The presence of lesions on crowns and stems and wilting of plants were monitored up to 9 days after transplanting (DAT). Data obtained were used to calculate the area under diseased plants progress curve (AUDPPC) and area under wilting plants progress curve (AUWPPC). Relative lesion extension (RLE) was obtained as the ratio of vertical lesion extension to stem length at 9 DAT. There was a 40% increase in the concentration of Si in the roots but not in the stems of bell pepper plants in the +Si treatment compared to the ,Si treatment. When comparing +Si to ,Si treatments, the AUDPPC was reduced by 15.4 and 37.5%, while AUWPPC was reduced by 29.1 and 33.3% in experiments 1 and 2, respectively. RLE values were reduced by 35% in the +Si treatment. Dry root weights increased by 23.7%, and stem weights were increased by 10.2% in the +Si treatment. Supplying Si to bell peppers roots can potentially reduce the severity of Phytophthora blight while enhancing plant development. [source] Biochemical Changes in Leaf Tissues of Taro [Colocasia esculenta L. (Schott)] Infected with Phytophthora colocasiaeJOURNAL OF PHYTOPATHOLOGY, Issue 3 2010Manas Ranjan Sahoo Abstract The changes in some biochemical parameters due to Phytophthora leaf blight infection were assessed in leaf tissues of one resistant (DP-25), two moderately resistant (Duradim and Jhankri) and one susceptible (N-118) genotypes of taro [Colocasia esculenta (L.) Schott]. Phytophthora spore suspension (15 000 spore/ml water) was sprayed onto the in vitro raised taro plantlets at 30 days after establishment in pots to induce disease. In comparison with the uninoculated leaves, blight infected leaves showed reduction in protein content and activity of nitrate reductase and increase in total soluble sugar, reducing sugar content and activities of acid phosphatase and alkaline phosphatase among the studied genotypes. Changes in biochemical parameters under induced blight stress as compared with uninoculated control were less in resistant genotypes than that in susceptible genotype. The deviations in biochemical contents were highest in susceptible genotype N-118. Based on the variations of above parameters under stress and non-stress control among the four tested genotypes, the overall pattern of changes was N-118 > Duradim > Jhankri > DP-25, which is in accordance with the pattern of increasing resistance. The resistant genotypes could be used for commercial cultivation and genetic improvement programme to develop resistant varieties to Phytophthora leaf blight disease. [source] Fungicide Effectiveness during the Various Developmental Stages of Peronophythora litchii In VitroJOURNAL OF PHYTOPATHOLOGY, Issue 7-8 2009Hancheng Wang Abstract Litchi downy blight caused by Peronophythora litchii is one of the most destructive diseases suffered by litchi in China. This study has evaluated the activities of the fungicides dimethomorph (DMM), azoxystrobin (AZB), famoxadone (FMD), metalaxyl (MTL), cymoxanil (CYX) and mancozeb (MCB) on the mycelial growth, sporulation, zoospores release, and germination of sporangia as well as of cystospores of P. litchii. Dimethomorph and MTL inhibited mycelial growth more effectively than the other fungicides tested. Mycelial growth was affected less by MCB, and only weakly by AZB, FMD and CYX. Sporangia production was more strongly reduced by DMM and MTL than by AZB, FMD, CYX or MCB. Zoospore release from the sporangia was most sensitive to AZB and FMD, less sensitive to MCB and insensitive to DMM, MTL and CYX. Direct germination of sporangia of P. litchii was the most strongly inhibited by AZB and FMD, followed by DMM and MCB, whilst the sensitivity of this life stage to MTL and CYX was relatively low. Germination of encysted zoospores of P. litchii was the most sensitive to AZB and FMD, followed by DMM. Mancozeb was moderately active, while MTL and CYX did not inhibit this development stage. This is the first report on the in vitro response of the litchi pathogen, P. litchii, to fungicides. These findings can be valuable tools in setting up efficient disease management programmes to control litchi downy blight. [source] Host Range of Australian Phoma ligulicola var. inoxydablis Isolates from PyrethrumJOURNAL OF PHYTOPATHOLOGY, Issue 7-8 2008S. J. Pethybridge Abstract Ray blight, caused by Phoma ligulicola var. inoxydablis is one of the most damaging diseases of pyrethrum (Tanacetum cinerariifolium [Trevir.] Sch. Bip.) in Australia. The pathogenicity of P. ligulicola var. inoxydablis to a range of ornamental and other plant species was tested to determine potential sources of inoculum into pyrethrum crops. Differences were identified in the host range of P. ligulicola var. inoxydablis isolates in this study in comparison with isolates reported from garden chrysanthemum (Chrysanthemum morifolium L.), most likely to be P. ligulicola var. ligulicola. Australian P. ligulicola var. inoxydablis isolates were unable to infect and cause disease following repeated inoculation to zinnia (Zinnia elegans L.), sunflower (Helianthus annuus L.), dahlia (Dahlia variabilis Desf.), and several cultivars of crisphead lettuce (Lactuca sativa L.). French marigold (Tagetes patula L.) was recorded as a susceptible host for this pathogen for the first time. Moreover, the susceptibility of annual chrysanthemum (Chrysanthemum carinatum L.) to infection by P. ligulicola var. inoxydablis was confirmed. Implications for disease management in Tasmanian pyrethrum fields are discussed. [source] Ultrastructural and Immunocytochemical Studies on Effects of Barley Yellow Dwarf Virus , Infection on Fusarium Head Blight, Caused by Fusarium graminearum, in Wheat PlantsJOURNAL OF PHYTOPATHOLOGY, Issue 1 2006Y. Liu Abstract The interactions between barley yellow dwarf virus (BYDV) and Fusarium head blight (FHB), caused by Fusarium graminearum, were studied in the two winter wheat cultivars (cvs.), Agent (susceptible to FHB) and Petrus (moderately resistant to FHB), using ultrastructural and immunocytochemical methods. Infections of wheat plants of both cvs. by BYDV increased susceptibility to FHB. BYDV infection caused numerous cytological changes in lemma tissue of both cvs. such as formation of vesicles in the cytoplasm, degradation of fine structures of chloroplasts of both cvs. and accumulation of large starch grains in the chloroplasts. Electron microscopical studies showed that the development of F. graminearum on spike surfaces was not affected in BYDV-infected plants. After penetration and intercellular growth in lemma tissue, defence responses to Fusarium infections were markedly reduced in BYDV-diseased plants compared to the tissue of virus-free plants. At sites of contact of fungal cells with host tissue, depositions of cell wall material were distinctly less pronounced than in tissues of virus-free plants of cv. Petrus. Detection of , -1,3-glucanases and chitinases in lemma tissue of cv. Agent revealed no appreciably increased accumulation of both defence enzymes in F. graminearum -infected virus-free and BYDV-infected tissues compared to the non-infected control tissue. On the other hand, in cv. Petrus, infection with F. graminearum induced a markedly enhanced activity of both enzymes 3 days after inoculation. The increase of both enzyme activities was less pronounced in BYDV-infected plants than in tissue exclusively infected with F. graminearum. Cytological studies suggest that in contrast to the susceptible cv. Agent postinfectional defence responses may play still an important role in the resistance of the moderately resistant cv. Petrus to FHB. [source] Use of a Mini-Dome Bioassay and Grafting to Study Resistance of Chickpea to Ascochyta BlightJOURNAL OF PHYTOPATHOLOGY, Issue 10 2005W. Chen Abstract A mini-dome bioassay was developed to study pathogenicity of Ascochyta rabiei and relative resistance of chickpea (Cicer arietanium). It was determined that the best condition for assaying pathogenicity of A. rabiei was to use 2 × 105 spores/ml as inoculum and to maintain a leaf wetness period of 24 h under mini-domes at a temperature between 16 and 22°C. This mini-dome pathogenicity assay was used to determine relative resistance of six chickpea cultivars (cvs) to isolates of two pathotypes of A. rabiei. Grafting was employed to detect any translocated factors produced in the chickpea plant that mediate disease response, which could help elucidate possible resistance mechanisms to Ascochyta blight. The six chickpea cv. were grafted in all possible scion,rootstock combinations, and then inoculated with isolates of two pathotypes of A. rabiei using the mini-dome technique. Results showed that self-grafted-resistant plants remained resistant and self-grafted-susceptible plants stayed susceptible, indicating the grafting procedure did not alter host response to infection by A. rabiei. Susceptible scions always exhibited high and similar levels of disease severity regardless of rootstock genotypes, and resistant scions always showed low and similar levels of disease severity when they were grafted onto any of the six rootstock genotypes. Orthogonal contrasts showed that scion genotypes determined disease phenotype, and that rootstock genotypes had no contribution to disease phenotype of the scions. The pathogenicity assay did not detect any translocated disease-mediating agents responsible for susceptibility or resistance in chickpea. Disease phenotypes of Ascochyta blight of chickpea were conditioned locally by scion genotypes. [source] | ||||||||||||||||||||||||||||