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Resistance Reaction (resistance + reaction)
Selected AbstractsInduced resistance of Norway spruce, variation of phenolic compounds and their effects on fungal pathogensFOREST PATHOLOGY, Issue 2 2000P. C. Evensen Summary Three clones of Norway spruce (Picea abies) were studied for their response to mass-inoculation with the blue-stain fungus Ceratocystis polonica. The effect of different pretreatments (fungal inoculation and wounding) before mass-inoculation was investigated for their possible role in an acquired resistance reaction. Pretreated trees showed enhanced resistance to the subsequent mass-inoculation relative to control trees that received no pretreatment. Furthermore, the fungal colonization of inoculated trees was less than that of wounded trees. The phenolic content of the bark, analysed by RP-HPLC, was compared in trees receiving different treatments. Trees inoculated with C. polonica had higher average concentration of (+)-catechin, taxifolin and trans-resveratrol than wounded trees. Both inoculated and wounded trees had higher average concentrations of these compounds than control trees. The effect of the phenolic extract of Norway spruce bark on the growth of the root rot fungus Heterobasidion annosum and the blue-stain fungi C. polonica and Ophiostoma penicillatum were investigated in vitro. Heterobasidion annosum was not negatively affected, and the extracts had fungistatic effects on the blue-stain fungi. The growth of O. penicillatum was more inhibited than the growth of the more aggressive C. polonica. [source] Histological investigation of stripe rust (Puccinia striiformis f.sp. tritici) development in resistant and susceptible wheat cultivarsPLANT PATHOLOGY, Issue 4 2006J. Moldenhauer The wheat cultivar Kariega expresses complete adult plant resistance against stripe rust, whereas cv. Avocet S is susceptible. Using confocal laser scanning microscopy, initial fungal penetration into flag leaves was identical in both cultivars, with directional germ-tube growth towards stomata that were penetrated without the formation of an appressorium, followed by differentiation of a substomatal vesicle, infection hyphae, haustorial mother cells and haustoria. During the following 4 days, further fungal development occurred more quickly in the resistant than in the susceptible cultivar. However, by 7 days postinoculation (dpi) the situation changed, with exponential growth of the pathogen occurring only in the susceptible line. Induced cellular lignification, a typical defence reaction of cereals, was observed at 4 dpi in the resistant cultivar, and 2 days later lignified tissue completely surrounded the fungal colonies. In the susceptible cultivar, isolated lignified host cells occurred at 6 dpi, and long, unbranched fungal hyphae outgrowing the resistance reaction were observed. [source] Patterns of accumulation of Bean common mosaic virus in Phaseolus vulgaris genotypes nearly isogenic for the I locusANNALS OF APPLIED BIOLOGY, Issue 3 2006M.M. Cadle-Davidson Abstract The I locus of Phaseolus vulgaris is genetically and phenotypically well described, conferring incompletely dominant, temperature-dependent resistance against viruses currently assigned to at least four Potyvirus species. Despite the fact that the resistance allele at this locus, the I gene, has been incorporated into nearly all bean germplasm worldwide, little is known regarding its resistance mechanism. In the present study, P. vulgaris lines nearly isogenic for I were challenged with Bean common mosaic virus (BCMV; genus Potyvirus) in order to investigate at the cellular level the temperature-dependent resistance reaction. Immunolocalisation and confocal laser scanning microscopy were employed to visualise the virus and to identify patterns of BCMV accumulation in resistant, susceptible and heterozygous genotypes. Virus was detected in all three genotypes regardless of temperature, supporting previous findings that BCMV accumulates in protoplasts containing the I allele. Genotype-specific and temperature-specific patterns of virus accumulation suggested a resistance mechanism that depends on host recognition of viral replication and/or local movement. [source] Reaction of Cotton Cultivars and an F2 Population to Stem Inoculation with Isolates Verticillium dahliaeJOURNAL OF PHYTOPATHOLOGY, Issue 5 2005Y. Bolek Abstract Four Verticillium dahliae isolates (V76, TS-2, PH, and V44) were used in screening four cotton cultivars (Pima S-7, Acala Prema, M-315 and Acala 44). Pima S-7 and Acala Prema gave the highest resistance reactions and Acala 44 was the most susceptible. Isolate V76 of V. dahliae was the most virulent. An interspecific cross between the resistant cv Pima S-7 (Gossypium barbadense) and the susceptible cv. Acala 44 (G. hirsutum) was made and the F2 population phenotyped for Verticillium wilt effect. Phenotyping of plant reaction to the disease was quantified by using a set of six growth parameters (number of healthy leaves, number of nodes, leaf weight, stem weight, leaf to stem ratio, and total shoot weight) measured 3 weeks after inoculation. The F2 phenotypic distribution of these parameters suggests that distribution is towards resistance and polygenic. Transgressive segregation also was observed. The number of healthy leaves and total shoot weight were found to be the best indicators of resistance. Results obtained in this study will be useful to quantify resistance to V. dahliae and identify the best parameters to phenotype in genetic studies. [source] Powdery Mildew Resistance in Barley Landraces from MoroccoJOURNAL OF PHYTOPATHOLOGY, Issue 5 2000J. H. Czembor Nineteen barley landraces collected from Morocco were screened for resistance to powdery mildew. The landraces originated from the collection at the Polish Gene Bank, IHAR Radzików, Poland. The fifteen landraces tested showed powdery mildew resistance reactions and 35 single plant lines were selected. Twenty-one of these lines were tested in the seedling stage with 30, four lines with 17 and another 10 lines with 23 differential isolates of powdery mildew, respectively. The isolates were chosen according to their virulence spectra observed on the Pallas isolines differential set. Nine lines (E 1029-1-1, E 1042-2-2, E 1050-1-1, E 1054-5-1, E 1056-2-5, E 1056-3-1, E 1061-1-1, E 1061-1-3 and E 1067-1-2) which originated from seven landraces showed resistance to all prevalent European powdery mildew virulence genes. The most frequent score was 2 and 16 lines showed this reaction for inoculation with most isolates used. The distribution of reaction type indicated that about 77% of all reaction types observed were classified as powdery mildew resistance (scores 0, 1 and 2). In all lines the presence of unknown genes alone or in combinations with specific ones was postulated. Four different resistance alleles (Mlat, Mla6, Mla14 and Mla12) were postulated to be present in 10 tested lines alone or in combination. Alleles Mlat, Mla6 and Mla14 were postulated to be present in four and Mla12 in two tested lines, respectively. The value of barley landraces for diversification of resistance genes for powdery mildew is discussed. Zusammenfassung Neunzehn Gerstenlandrassen aus Marokko wurden auf ihre Resistenz gegenüber dem Echten Mehltau untersucht. Diese Landrassen wurden in der Sammlung der Polish Gene Bank, IHAR, Radzikow, Polen aufbewahrt. Fünfzehn der geprüften Rassen zeigten Echte Mehltau-Resistenz und davon wurden 35 einzelne Pflanzenlinien selektiert. 21 dieser Linien wurden als Sämlinge gegenüber 30, 4 Linien gegenüber 17 und weitere 10 Linien gegenüber 23 differentialen Echten Mehltau-Isolaten geprüft. Diese Isolate wurden an Hand von ihren Virulenzspektren bei dem Pallas-Isoline-Differential-Set ausgewählt. Bei 9 Linien (E 1029-1-1, E 1042-2-2, E 1050-1-1, E 1054-5-1,E1056-2-5, E 10456-3-1, E 1061-1, E 1061-1-3 sowie E 1067-1-2), die von 7 Landrassen stammten, konnte eine Resistenz gegenüber allen bedeutenden europäischen Virulenzgenen festgestellt werden. Am häufigsten wurde die Resistenznote 2 vergeben, 16 Linien zeigten diese Reaktion nach einer Inokulation mit den meisten angewandten Isolaten. Die Verteilung des Reaktionstyps deutete daraufhin, dass ca. 77% der beobachteten Reaktionstypen als Echte Mehltau-Resistenz (die Note 0,1 und 2) eingestuft werden konnten. Das Vorkommen von unbekannten Genen, ob alleine oder in Kombination mit einem spezifischen Gen, wurde in allen Linien postuliert. Ebenfalls postuliert wurde das Vorhandensein von vier unterschiedlichen Resistenzallelen (Mlat, Mla6, Mla14 und Mla12), entweder alleine oder in Kombinationen, in den 10 geprüften Linien. Die Allele Mlat, Mla6 und Mla14 wurden in 4, das Allel Mla12 in 2 der getesteten Linien postuliert. Die Relevanz von Landrassen in der Erweiterung von Resitenzgenen gegenüber dem Echten Mehltau in der Gerste wird diskutiert. [source] Claviceps purpurea: molecular aspects of a unique pathogenic lifestyleMOLECULAR PLANT PATHOLOGY, Issue 5 2004PAUL TUDZYNSKI SUMMARY Claviceps purpurea is a ubiquitous pathogen of cereals and grasses, causing Ergot disease, which results in substitution of grains by sclerotia. These overwintering structures contain ergot-alkaloids, which can cause severe intoxication in mammals. C. purpurea is an interesting model system for the study of host,pathogen interaction. It displays strict organ specificity, attacking exclusively young grass ovaries. It is optimally adapted to this special niche of infection, probably by mimicry of pollen tubes: there are no resistance genes known, and no effective resistance reactions can be detected in the early steps of infection. In this early phase of host tissue colonization the fungus shows directed, almost unbranched growth towards the base of the ovary. Thus, C. purpurea represents one of the few systems in which directed growth in filamentous fungi can be studied. Finally, the fungus behaves as a true biotroph in planta, although it can be easily grown in axenic culture. We describe here the tools available to study this interesting pathogen, report on recent molecular investigations concerning the role of cell-wall-degrading enzymes and of reactive oxygen species in this specialized interaction, and present an update of the signalling cascades involved in early events of pathogenesis. [source] | |||||||||||||||||||