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  • 1
    Electronic Resource
    Electronic Resource
    The occurrence, characteristics and distribution in the United Kingdom of resistance to phenylamide fungicides in Bremia lactucae (lettuce downy mildew) (1987)
    Oxford, UK : Blackwell Publishing Ltd
    Plant pathology 36 (1987), S. 0 
    Details
    ISSN: 1365-3059
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Failure to control Bremia lactucae (lettuce downy mildew) with metalaxyl in an intensive lettuce-producing region of Lancashire at the end of 1983 was shown to be due to the occurrence of a high level of resistance to this fungicide (isolates capable of growth at 〈 100 μg/ml metalaxyl). During most of 1984, metalaxyl-resistant isolates were obtained from numerous sites but all within a 20-km radius of the initial outbreak. Thereafter, at the end of 1984 and during 1985, metalaxyl-resistant isolates were recovered from most major lettuce-producing regions in the UK with protected crops more affected than field crops. AH metalaxyl-resistant isolates tested were identical in their response to fungicide, sexual compatibility type (B2) and virulence phenotype, probably representing a clone from a single origin. The resistant pathotype was virulent on resistance factors R 1-10 and 12-15 but lacked virulence for R 11 and 16-18. This was also the most common virulence phenotype among sensitive isolates collected at the same time. Cross-resistance to other phenylamide fungicides was demonstrated but isolates resistant and sensitive to phenylamide showed a similar response to the unrelated systemic fungicides propamocarb and fosetyl-Al. An F1 sexual progeny isolate from a cross between a phenylamide-sensitive and a phenylamide-resistant isolate (presumed heterozygous at the locus or loci regulating response to phenylamide fungicides) exhibited an intermediate response to phenylamide fungicides. No isolates of this type were obtained from the field. At the high concentrations affecting spore germination, phenylamide fungicides exhibited lower activity against a resistant isolate compared with a sensitive isolate. The findings are discussed in relation to future control strategies, the population biology of the fungus and possible directions for lettuce breeding programmes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3059.1987.tb02237.x
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  • 2
    Electronic Resource
    Electronic Resource
    The inheritance of specific virulence in Bremia lactucae (downy mildew) to match resistance factors 1, 2, 4, 6 and 11 in Lactuca sativa (lettuce) (1983)
    Oxford, UK : Blackwell Publishing Ltd
    Plant pathology 32 (1983), S. 0 
    Details
    ISSN: 1365-3059
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: The inheritance of specific virulence in Bremia lactucae was studied by hybridizing two isolates which differed in their virulence on host cultivars carrying the resistance factors R1, R2, R4, R6 and R11. Avirulence on R1, R2, R4 and R11 was dominant to virulence and the segregation conformed to that expected for alleles at single loci, although reactions on R4 were not always dearly defined. The loci conditioning avirulence on R2 and R11 were probably linked. It was difficult to classify the reactions of isolates on R6 and the ratios obtained could not readily be interpreted in Mendelian terms. Since no segregation was observed for reaction on R3, R5, R7, R8, R9 and R10 it was concluded that the genes determining virulence on these factors occurred at the same loci in both isolates, Sexual compatibility type (B1 and B2) segregated with a ratio of 1:1.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3059.1983.tb01317.x
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  • 3
    Electronic Resource
    Electronic Resource
    The genetic control and expression of specificity in Bremia lactucae (lettuce downy mildew) (1984)
    Oxford, UK : Blackwell Publishing Ltd
    Plant pathology 33 (1984), S. 0 
    Details
    ISSN: 1365-3059
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: The inheritance of specific virulence in Bremia lactucae was studied in crosses involving 12 heterothallic isolates of the fungus. In one cross, virulence to eight of the II specific resistance factors examined segregated in the F1 generation. Although there were exceptions, most of the data were consistent with the hypothesis that pathogenicity was controlled by independent single loci with avirulence dominant to virulence. Linkage between loci determining virulence on R2 and R11 was confirmed. Loci controlling virulence on R5 and R8 also appeared to be linked but these may be identical R-factors. Contrary to a previous suggestion, the locus determining virulence to R10 was independent of that for R5/R8. The expression of virulence to three R-factors (Rl, R4 and R5/R8) was influenced by independent second loci. The presence of a dominant allele at the second locus inhibited avirulence. The expression of avirulence on R6 seemed to be influenced by modifier genes and environment in some isolates. Although the cultivars Mildura, Bourguignonne, Sucrine and Captain were originally thought to contain a single resistance factor, these data suggest that Sucrine carries R5/R8 in addition to R10 whilst Mildura may carry Rl in addition to R3. The stock of Bourguignonne appeared to be a mixture of resistance genotypes. The data add additional support to the suggestion that Capitan (Rll) may carry two resistance factors.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3059.1984.tb01334.x
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  • 4
    Electronic Resource
    Electronic Resource
    Further characterization of field resistance in lettuce to Bremia lactucae (downy mildew) (1985)
    Oxford, UK : Blackwell Publishing Ltd
    Plant pathology 34 (1985), S. 0 
    Details
    ISSN: 1365-3059
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: The development of five Bremia lactucae isolates on the field-resistant crisphead lettuce cultivar Iceberg was compared under field conditions with that on the more susceptible crisphead cultivar Ithaca. With each of five isolates, the epidemic developed more rapidly on Ithaca than Iceberg; lesions on Ithaca were more numerous, larger and sporulated more profusely than on Iceberg. There was no evidence for adaptation of isolates to Iceberg, which provides some additional evidence that the resistance of this cultivar could be non-differential (horizontal). There was, however, evidence of non-specific differences between isolates in their quantitative virulence.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3059.1985.tb01397.x
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  • 5
    Electronic Resource
    Electronic Resource
    The identification and characteristics of field resistance to lettuce downy mildew (Bremia lactucae Regel) (1981)
    Springer
    Euphytica 30 (1981), S. 707-717 
    Details
    ISSN: 1573-5060
    Keywords: Lactuca sativa ; lettuce ; Bremia lactucae ; downy mildew ; field resistance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Eighty-one accessions of three Lactuca species which showed no recognisable race specific resistance to Bremia lactucae when tested in the laboratory as seedlings, exhibited different degrees of susceptibility when exposed to natural field infection. As a group, crisp genotypes had less mildew and a slower rate of disease development than other types of lettuce. Wild forms of Lactuca sativa and Lactuca serriola were particularly susceptible. In a further trial, the low field susceptibility of three lettuce cultivars (Iceberg, Batavia blonde de Paris and Grand Rapids) was confirmed. Disease development on cv. Iceberg was compared to that on the highly susceptible cv. Hilde in experiments where the two cultivars were grown either in close proximity or in isolation. The absolute level of attack on cv. Iceberg depended upon disease pressure and differences between the two types only became apparent approximately 8 wk after sowing.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00038799
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  • 6
    Electronic Resource
    Electronic Resource
    A demonstration of the inheritance of field resistance to lettuce downy mildew (Bremia lactucae Regel.) in progeny derived from cv. Grand Rapids (1983)
    Springer
    Euphytica 32 (1983), S. 161-170 
    Details
    ISSN: 1573-5060
    Keywords: Lactuca ; lettuce ; Bremia lactucae ; downy mildew ; field resistance ; inheritance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary The inheritance of field resistance to downy mildew in lettuce derived from cv. Grand Rapids was studied in F2, F3 and F4 progeny from a cross with the more susceptible cv. Lobjoits Green Cos. The results for 32 randomly produced F3 families and the F2 population corresponded closely although the absolute level of resistance varied from season to season according to disease pressure and environmental conditions. The field resistance character showed a quantitative pattern of inheritance but the rapid response to selection at F3 implied that only a few genes may be involved. F4 families raised from families selected from the two extremes of the F3 distribution fell into distinct categories with resistance levels corresponding to that of their F3 parents. An association between resistance and morphological features of the resistant parent was present at F2 but not in subsequent generations when individuals and families which were as resistant as cv. Grand Rapids and yet bore little morphological resemblance to this cultivar were readily recovered.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00036876
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  • 7
    Electronic Resource
    Electronic Resource
    The location and characteristics of novel sources of resistance to Bremia Lactucae Regel (downy mildew) in wild Lactuca L. Species (1981)
    Springer
    Euphytica 30 (1981), S. 659-668 
    Details
    ISSN: 1573-5060
    Keywords: Bremia lactucae ; downy mildew ; Lactuca species ; lettuce ; resistance ; physiologic races
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Twenty-one accessions of 3 wild Lactuca species which could be hybridised with L. sativa, the cultivated lettuce, were inoculated at different stages of plant development with 3 multivirulent isolates of Bremia lactucae. Nineteen sources of resistance to B. lactucae, not attributable to the previously recognised resistance factors 1–11 were identified. Two lines of L. serriola showed similar resistance patterns as lines carrying R11. The resistance of some accession was incomplete particularly at the seedling stage and this phenomenon may be race specific. Tests on segregating F2 populations of crosses between 2 different L. serriola accessions and L. sativa cultivars showed that the resistance in one line (LSE/18) appears to be inherited as a single dominant gene, which is sometimes incomplete in expression and allelic to either Dm6 or R7. The segregation patterns for resistance in PI 281876 did not give readily interpretable ratios. To assess the frequency of occurrence in B. lactucae populations of virulence factors to overcome this novel resistance, 11 of the novel sources of resistance were inoculated with numerous collections of the pathogen from the UK, Czechoslovakia and elsewhere and found to show a high level of resistance.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00038794
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  • 8
    Electronic Resource
    Electronic Resource
    The use of sexual progeny of Bremia Lactucae Regel to improve the efficiency of selection for race-specific resistance genes to this fungus in lettuce (1983)
    Springer
    Euphytica 32 (1983), S. 475-478 
    Details
    ISSN: 1573-5060
    Keywords: Lactuca sativa ; lettuce ; Bremia lactucae ; downy mildew ; resistance breeding ; sexual progeny
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00021457
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