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  • 1
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Plant pathology 33 (1984), S. 0 
    ISSN: 1365-3059
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: The development of powdery mildew on seven spring barley varieties lacking effective major resistance factors was compared in a small-plot field trial. Differences were observed at later growth stages indicating partial resistance in some varieties. Latent period and sporulation capacity were examined on the fifth or sixth leaf of these varieties plus several known to be susceptible, using plants raised under spore-free conditions. Latent period was extended in most partially resistant varieties compared with susceptible controls, more so at 5°C than at 10°C. Cumulative total spore production per colony over the 16-day sporulation period differed markedly between varieties, the most resistant yielding one-third as many spores as the susceptible controls. There was evidence that these resistance components were correlated with each other and with previous estimates of infection frequency. The significance of this finding, in relation to selection for improved levels of partial resistance, is discussed.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Plant pathology 43 (1994), S. 0 
    ISSN: 1365-3059
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: A molecular method is described to aid identification of the obligate parasite Polymyxa and discriminate between species (P. betae and P. graminis) and isolates. DNA was extracted from zoospores, resting spores and roots infected with P. betae and P. graminis and compared with that from negative control plants that were not inoculated with Polymyxa but were grown at the same time under the same conditions. The ribosomal internal transcribed spacers and 5.8S rDNAs were amplified by the polymerase chain reaction and digested with restriction enzymes to detect molecular differences between the species and isolates. There were differences between P. betae and P. graminis and two subgroups within P. graminis but so far this has not been correlated with any other biological property.
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  • 3
    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 host range of Polymyxa betae on common arable weed species in Britain was determined by growing plants in naturally infested soil and examining their root systems for the presence of resting spores (cystosori). Of the 24 species tested, only Atriplex patula and Chenopodium album of the Chenopodiaceae, and Silene alba of the Caryophyllaceae, were found to be heavily infected. S. alba is a newly recorded host species for Polymyxa. The host specificity of isolates of P. betae from Beta vulgaris, C. album and A. patula was investigated by observing which of 11 test plants could be infected by the isolates obtained from this soil. Three main biotypes of P. betae appeared to be distinguishable: one which was able to infect all chenopodiaceous species; one which had a narrower host range; and one which was able to infect S. alba. The role of weed species in the epidemiology of rhizomania is discussed.
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  • 4
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Plant pathology 40 (1991), S. 0 
    ISSN: 1365-3059
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: The effects of soil temperature on infection of sugar-beet roots by the soil-borne fungus Polymyxa betae were investigated in controlled environments. Pre-germinated seeds were sown in pots of naturally infested soil and seedlings sampled at frequent intervals over a period of several weeks. Within the range 10-30°C, the optimum soil temperature for infection was c. 25°C; the time between sowing and the first detectable infection was shortest and the subsequent rate of infection most rapid at this temperature. No infection was observed over 80 days at 10°C.Both root and shoot dry weight were reduced on plants growing in infested soil at 15, 20 and 25 C compared with those growing in uninfested soil. In general, root growth was more severely affected than shoot growth and the effects were most pronounced at 20°C. These results were confirmed in a subsequent experiment in which P. betae-infected root material was used as the inoculum. In addition to its role as the vector of beet necrotic yellow vein virus (the cause of Rhizomania disease), the significance of P. betae as a plant pathogen in its own right is discussed.
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  • 5
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Plant pathology 39 (1990), S. 0 
    ISSN: 1365-3059
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: A 2-year survey of soils from a total of 208 fields, using sugar-beet seedlings as bait plants, showed Polymyxa betae to be ubiquitous in the sugar-beet-growing areas of Britain. It was detected in some soils which had not grown a host crop for up to 17 years. However, infection of roots was relatively infrequent in plant samples taken from 134 survey fields in early summer and the density of colonization always low. Three other non-mycelial fungi, Olpidium brassicae, Lagena radicicola and Rhizophydium graminis were also common parasites of sugar-beet roots detected in soil bioassays. Infection of plant samples by O. brassicae was particularly severe.
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  • 6
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Plant pathology 43 (1994), S. 0 
    ISSN: 1365-3059
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: In a survey of fungi causing seedling diseases of sugar beet using a soil bioassay, Aphanomyces cochlioides and Pythium spp. were found to occur in 39% and 31%, respectively, of 341 sugar-beet fields selected in a stratified random sample in England, The frequency of A. cochlioides-infested soils varied widely in the different sugar-beet growing areas of the country. Soil pH was the single factor most strongly associated with the distribution of the pathogen, but regression models applied to combinations of factors indicated that soil texture and the interval between sugar-beet crops were also relevant to its frequency. It was detected less often in soils of high pH (≥ 75). heavy texture and where the interval between sugar-beet crops exceeded 5 years. No significant associations were found between the proportion of soils with Pythium spp. and soil or cropping factors.
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  • 7
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Plant pathology 40 (1991), S. 0 
    ISSN: 1365-3059
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: In a national survey of the incidence of powdery mildew (Erysiphe betae) in sugar beet in Britain, between 1980 and 1989, in which between 335 and 717 fields were inspected at the end of August each year, the average crop area infected ranged from 2% in 1986 to 68% in 1989. The effect of various climatic factors that might be expected to influence powdery mildew development over this period was examined, using meteorological records from Broom's Barn Experimental Station, Using simple linear regression analyses, a significant association was found between disease incidence and both air temperature and rainfall incidence in the period April-August, However, air temperature and frost incidence in some winter months were also closely associated with the incidence of powdery mildew in the following crop.Combinations of these variables were examined in stepwise multiple-regression analyses, The model of best fit, incorporating winter frost incidence with summer temperature and rainfall incidence, accounted for 95% of the variation. Model validation procedures demonstrated the superiority of this model over those involving single variables. Nevertheless, for forecasting purposes, the best correlation was found between the crop area infected at the end of August each year and the number of days with a ground frost in the preceding February and March. This single climatic variable accounted for 82% of the variation and its potential use to forecast powdery mildew incidence in the national sugar-beet crop is discussed.
    Type of Medium: Electronic Resource
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  • 8
    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: The response of epidermal cells to attempted penetration by Erysiphe graminis was examined in the fifth leaf of 13 barley lines selected for partial resistance. In leaf segments fixed and stained 72 h after inoculation cell reactions were classified as susceptible or as exhibiting non-hypersensitive or hypersensitive resistance. The proportion of cells with each type of reaction varied in a continuous manner among the lines and there were significant differences between lines in the levels of non-hypersensitive and hypersensitive resistance. Crosses were made between lines exhibiting high and low levels of each resistance mechanism. Fifty challenged epidermal cells per duplicate leaf segment were examined on 45-50 F2 plants derived from two such crosses. The frequency distribution of each of the three types of cell reaction in the fifth leaf was found to be continuous and, in general, normally distributed and in no case was there a significant difference between parent and progeny mean values, suggesting that the two resistance mechanisms were under the control of several genes showing predominantly additive gene action.
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  • 9
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Plant pathology 32 (1983), S. 0 
    ISSN: 1365-3059
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: The development of powdery mildew on five barley varieties selected for partial resistance in the field and lacking identifiable, effective race-specific resistance factors was examined. Inoculation tests demonstrated that a reduction in the number of colonies was a major component of this resistance. Microscopic examination of segments from the fourth and fifth leaf revealed several stages at which colony development was arrested. The failure of individual penetrations to establish compatible colony growth was classified as being due either to hypersensitive or to non-hypersensitive resistance in host epidermal cells. Varying proportions of these two types of resistance mechanism were evident in all varieties examined, including the susceptible controls. In four resistant varieties, one or other mechanism predominated. The possibility of enhancing partial resistance by combining sources in which different mechanisms operate is discussed.
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  • 10
    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 effect of sowing date on the infection of sugar-beet seedlings by Polymyxa betae was examined in a small-plot experiment on a naturally infested site. Seed was sown on seven occasions at weekly intervals from late March to early May. From each sowing, plant samples were taken at approximately weekly intervals over a period of 7 weeks. The extent of root infection by P. betae and the dry weight of plants was determined at each sampling date, and the progress of infection and rate of plant growth were examined against time and thermal time. Infection occurred sooner after sowing and the subsequent rate of fungal development was more rapid in late-sown than in early-sown plants. Early sowing allowed germination and growth of sugar beet at temperatures too low for fungal infection. The growth of late-sown plants appeared to be reduced by P. betae infection. The implications of these findings for the development of rhizomania disease are discussed.
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