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  • 1
    ISSN: 1365-3059
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: On the basis of pathogenicity tests on green berries or hypocotyls of coffee and by morphological and biochemical characteristics in culture, 31 isolates of Colletotrichum were classified into C. kahawe (24 isolates), C. gloeosporioides (six isolates) or C. acutatum (one isolate). Within these groups of isolates, vegetative compatibility groups (VCGs) were determined by complementation tests with mutants in the nitrate assimilation pathway. There were distinct incompatibility barriers between the three species. Among the C. gloeosporioides group, the three isolates tested were self-compatible but incompatible with each other. Within C. kahawe, 18 isolates were self-compatible and only one main VCG was detected. However, partial compatibility in C. kahawe was also indicated by variation in the intensity of heterokaryon formation between different pairs of isolates and between different types of mutant. The existence of only one VCG in C. kahawe is consistent with the low level of variation found in previous work on DNA polymorphism.
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  • 2
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Plant pathology 42 (1993), S. 0 
    ISSN: 1365-3059
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: During a survey of root diseases of pea in Denmark, a new genetic variant of Fusarium oxysporum f.sp. pisi was isolated from vining peas in two widely separated geographical regions. In terms of pathogenicity on a set of differential pea lines, the Danish isolated closely resembled a race 6 isolate from the United States, DNA extracts of the isolates, restricted with the endonuclease HindIII, then probed with a homologous repetitive genomic fragment from the plasmid pDG106 by the Southern hybridization technique, gave a unique‘fingerprint’pattern distinctly different from the American race 6 and all other known races. When probed with pDG312, containing a homologous ribosomal repeat unit, the pattern obtained for the Danish isolates was indistinguishable from races 1, 5 and 6 but distinctly different from 2A and 2B. The Danish isolates represent a separate vegetative compatibility group because they are compatible with each other but incompatible with the other known races. In pigmentation the new variant resembled races 1, 5 and 6 for the first 8-12 days, after which it began to secrete a dark purple pigment resembling that of race 2A and 2B. Until an additional line in the host differentials can separate the new genetic variant it should be considered a subgroup of F. oxysporum f. sp. pisi race 6.
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  • 3
    ISSN: 1439-0523
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Six accessions belonging to four subspecies of Brassica rapa, including three accessions of B. rapa subsp. sylvestris, were crossed with B. oleracea subsp. alboglabra in order to develop a series of synthetic B. napus lines with a common C genome but contrasting A genomes. Different A genomes had significant effects on the efficiency of B. napus resynthesis and the sexual compatibility of the synthetic lines with oilseed rape cultivars. The synthetic lines were used to investigate the effect of A genome substitution on the resistance of B. napus to infection by Leptosphaeria maculans, and to explore the potential for the use of wild forms of B. rapa in oilseed rape breeding programmes. Synthetic lines derived from two wild accessions of B. rapa, and their F1 hybrids with oilseed rape cultivars, expressed high levels of resistance to L. maculans in glasshouse experiments. One of these lines also expressed high levels of resistance in field experiments in England and Australia when exposed to a genetically diverse pathogen population. All other synthetic lines and cultivars were highly susceptible in both glasshouse and field experiments. F1 hybrids between oilseed rape cultivars and synthetic lines derived from B. rapa subsp. chinensis were significantly more susceptible than either parent.
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  • 4
    Electronic Resource
    Electronic Resource
    Oxford, U.K. and Cambridge, USA : Blackwell Science Ltd
    Plant pathology 45 (1996), S. 0 
    ISSN: 1365-3059
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Two monoclonal antibodies (MAbs) were produced against soluble antigens from the ‘Ascochyta complex’ fungi. Specificity of MAbs was tested by ELISA using antigen-coated wells. MAbs secreted by the monoclonal hybridoma cell line JIM 44 recognized epitopes present in the antigen preparations from Mycosphaerella pinodes and Phoma medicaginis var. pinodella, but not those present in preparations from Ascochyta pisi. At high tissue culture supernatant concentration, MAbs produced by the monoclonal line JIM 45 recognized epitopes from all three fungi, however, on dilution of MAb the antigens from A. pisi were recognized preferentially to those from M. pinodes and P. medicaginis var. pinodella. On the basis of heat and periodate treatment of the antigens from the three fungi it can be concluded that the epitope recognized by JIM 44 is carbohydrate in nature, whereas that recognized by JIM 45 is proteinaceous in nature, carried on a glycoprotein antigen. Antigen preparations from other fungi, including other pea pathogens, non-pathogens associated with pea and other fungi closely related to the ‘Ascochyta complex’, were not detected with either of the two MAbs. Antigen preparations from peas could be used to differentiate healthy and infected seeds in a dot-blot assay, therefore indicating the potential of using the MAbs in the development of a diagnostic test for infection of Pisum seeds by the ‘Ascochyta complex’ fungi.
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  • 5
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Plant pathology 41 (1992), S. 0 
    ISSN: 1365-3059
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: The infection of three resistant and two susceptible inbred lines of Pisum sativum by Mycosphaerella pinodes is described for the first time. Two types of resistance, one expressed in epicotyls and one in leaves, were found in all three resistant lines. On epicotyls of susceptible lines, abundant appressoria and penetrations occurred after a short period of hyphal growth. On epicotyls of resistant lines, hyphae grew extensively but rarely formed appressoria, and these failed to penetrate the cuticle. Attempted penetration was associated with the rapid death of 2–6 epicotyl cells, resembling a hypersensitive reaction. In contrast, resistance of leaves, which was only expressed after penetration, involved localization of the fungus by a mechanism involving delayed leaf cell death. It is suggested that a combination of these two types of resistance might provide effective protection against M. pinodes.
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  • 6
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Plant pathology 36 (1987), S. 0 
    ISSN: 1365-3059
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: In a series of growth room experiments in which leaves of Brassica napus var. oleifera were inoculated with ascospores or pycnidiospores of Leptosphaeria maculans successful infections progressed through three consecutive phases. Initial establishment in the mesophyll was succeeded by a phase of intercellular exploration, when hyphal proliferation was highly variable and host cell necrosis always ensued, and then by a systemic phase when hyphae were consistently sparse. Host cells associated with the hyphal front were capable of autofluorescence, accumulation of vital stains and plasmolysis, indicating that they were viable and that the pathogen was biotrophic throughout this sequence. During either of the first two phases permanent fungistatic containment, involving the formation of vesicles by disintegration of the hyphae, often occurred. Localization at the first phase was symptomless; at the second it was signified by a lesion with a clearly defined margin.There was a negative correlation between biotrophic potential and necrotrophic potential of three pathogenic isolates, on both the moderately susceptible cultivar Primor and the resistant cultivar Jet Neuf. As leaves aged, a progressively larger proportion of infections failed to become systemic. With increasing inoculum load, symptomless localization of infection diminished, the phase of necrosis extended, and the probability of irreversible systemic development increased.
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  • 7
    ISSN: 1365-3059
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Development of stem cankers in seedlings of Brassica napus var. oleifera inoculated with Leptosphaeria maculans was studied in growth cabinets. As the pathogen progressed from the petiole into the stem, hyphae invaded parenchyma cells for the first time, initiating a necrotrophic phase which resulted in the formation of a lesion. Ultimate containment of the pathogen was associated with a sequence of host reactions including lignification, cambium formation and callose deposition at the perimeter of the lesion. Two isolates of L. maculans differed in the pattern of stem infection. One was confined to the cortex and the other passed through the leaf gap into the pith. Variation in response between cultivars Rapora, Primor and Jet Neuf modified these two colonization patterns but did not eliminate the main differences. There were qualitative and quantitative differences in host cell reactions. The significance of these findings is discussed in relation to differences in resistance of the cultivars in the field.
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  • 8
    ISSN: 1365-3059
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Natural epidemics of Leptosphaeria maculans in cultivated populations of Brassica napus var. oleifera were predominantly monocyclic, involving a sequence of five phases; latent infection of the lamina, leaf lesion expression, symptomless systemic growth down the petiole, latent infection of the stem, and stem canker development. This sequence potentially terminated in severe stem cankers if initiated from ascospore infection of any leaf between a plastochron index of PI =n+ 0.5 and n+1.0 until plant growth stage 3.1 of the Harper & Berkenkamp scale. At PI 〈 n+ 0.5, infection was rare and at PI 〉 n+ 1.0, the infection sequence was usually terminated by leaf abscission. Differential effects of ambient temperature on the rates of progress of infection and leaf development determined whether abscission occurred before infection reached the stem. Based on these interrelationships, a system for predicting the incidence of severe stem cankers is proposed.
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  • 9
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Plant pathology 34 (1985), S. 0 
    ISSN: 1365-3059
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: In growth room regimes arranged to simulate field conditions which coincide with natural infection of oilseed rape by Leptosphaeria maculans, leaf inoculation resulted in systemic infection. After colonizing intercellular spaces in the spongy mesophyll of the lamina, the fungus reached a vascular strand and spread down the petiole mainly in xylem vessels or between cells of the xylem parenchyma and cortex, eventually invading and killing cells of the stem cortex and causing the stem canker symptom. The intercellular systemic phase of growth, which was biotrophic and virtually sytnptomless, occurred under a wide range of temperatures.
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  • 10
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Plant pathology 35 (1986), S. 0 
    ISSN: 1365-3059
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: When a range of genotypes of the genus Pisum was inoculated with Ascochyta pisi some remained uninfected or symptomless whereas the reactions of others ranged from a hypersensitive resistance through various levels of susceptibility to almost lethal infection. This variation, categorized on a six-class scale, was used to describe the reactions of 57 isolates of A. pisi collected from pea crops widely distributed in Britain when inoculated on to 14 differential lines of Pisum. Five major pathotype groups were distinguished and a set of lines nominated as standard differential hosts.
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