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  • 1
    Electronic Resource
    Electronic Resource
    Association of double-stranded RNA with whitefly-mediated silvering in squash (1990)
    Oxford, UK : Blackwell Publishing Ltd
    Plant pathology 39 (1990), S. 0 
    Details
    ISSN: 1365-3059
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: A disorder of unknown aetiology appearing as silvering on squash (Cucurbita pepo) leaves has become prevalent in south Florida. Typical symptoms, observed after 2 weeks of exposure to adults of Bemisia tabaci, the sweet potato whitefly (SPWF) include vein clearing followed by silvering of whole leaves. Fruits from affected plants are blanched or streaked longitudinally. The silverleaf syndrome was not mechanically transmissible when crude extracts of symptomatic leaves were used as inoculum. Two sizes of double-stranded RNA (dsRNA) of c. 4.6 and 4.2 kilobase pairs (kbp) were consistently observed in leaf extracts of caged, whitefly-infested, symptomatic plants. In contrast, caged plants not exposed to whiteflies showed no symptoms and contained no detectable dsRN A. In addition, squash plants exposed to SPWF colonies from California neither developed silverleaf symptoms nor contained any dsRNA. Double-stranded RNA could also be readily detected in whitefly-infested yellow summer squash and zucchini from the field. However, asymptomatic eggplant and watermelon infested with SPWF from nearby fields did not contain detectable dsRNA. Dot-spot hybridization assays using an RNA-specific probe detected homologous sequences in both adults and nymphs of SPWF that induced silverleaf symptoms but not in adults and nymphs of SPWF that could not induce silverleaf symptoms. These results, along with the non-endogenous nature of the detected dsRNA suggest that the dsRNA is or is associated with the causal agent of whitefly-mediated leaf silvering in squash.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3059.1990.tb02530.x
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  • 2
    Electronic Resource
    Electronic Resource
    Association of stomatal frequency and morphology in Lycopersicon species with resistance to Xanthomonas campestris pv. vesicatoria (1992)
    Oxford, UK : Blackwell Publishing Ltd
    Plant pathology 41 (1992), S. 0 
    Details
    ISSN: 1365-3059
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Study of the stomata and leaf epidermis of eight Lycopersicon species has revealed a relationship between frequency of stomata, stomatal size and some morphological leaf characteristics, and resistance to bacterial leaf spot caused by Xanthomonas campestris pv. vesicatoria. Significant correlations were found between the stomatal frequency in both adaxial and abaxial leaf epidermis and the number of bacterial lesions per leaf area (r= 0.70 and 0.68, respectively) and the frequency of stomata in both adaxial and abaxial epidermis and disease incidence (percentage of diseased plants) (r=0.87 and 0.80, respectively) for all the Lycopersicon species and one hybrid tested. A correlation was also found between disease incidence and number of bacterial lesions per leaf area (r= 0.85). The length and width of stomata were correlated with frequency of stomata in adaxial and abaxial epidermis (r= 0.85, 0.75, 0.89 and 0.90, respectively). The stomatal width was correlated with the number of bacterial lesions per cm2 (r=0.82; P= 0.0065). Scanning electron microscopic studies of the leaf surface and stomata indicated that other morphological features such as the raised stomatal complex in L. hirsutum and persistent, hydrophobic waxy coating of the epidermis in L. peruvianum may also be relevant in disease response.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3059.1992.tb02334.x
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  • 3
    Electronic Resource
    Electronic Resource
    Histopathological changes associated with silverleaf syndrome in squash (1995)
    Oxford, UK : Blackwell Publishing Ltd
    Plant pathology 44 (1995), S. 0 
    Details
    ISSN: 1365-3059
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Silverleaf syndrome on squash (Cucurbita pepo) is characterized by vein clearing, and leaf whitening, and has been associated with the presence of nymphs of Bemisia tabaci (sweetpotato whitefly), and the presence of two double-stranded RNAs (4·2 and 4·6 kb) in symptomatic leaves. However, the aetiology of the disorder remains unknown. Anatomical studies using transverse and paradermal sections from symptomatic leaves of C. pepo cv. Dixie showed turgescent, aligned adaxial epidermal cell layer, flat cuticle and the presence of sub-epidermal spaces. Histochemical studies failed to reveal any breakdown in the cellulose cell walls; however, the cuticular layer, the pectin layer and cellulose wall of epidermal cells formed a fiat compact structure. Some changes were observed in the lipid content, with the presence of lipid bodies near cell wall membranes. Sodium dodecyl sulphate-polyacrylamide gel electrophoresis of preparations of symptomatic squash leaves, partially purified by differential centrifugation, revealed a protein with a molecular mass of about 48 k Da that was not found in comparable preparations of asymptomatic leaves. This protein was localized by immunological staining in the spongy mesophyll cells and in the layer of bundle sheath associated with sieve elements and companion cells of the leaf phloem.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3059.1995.tb02783.x
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  • 4
    Electronic Resource
    Electronic Resource
    Inheritance of resistance to Pyrenochaeta lycopersici in tomato (1978)
    Springer
    Euphytica 27 (1978), S. 75-79 
    Details
    ISSN: 1573-5060
    Keywords: Lycopersicon esculentum ; tomato ; Pyrenochaeta lycopersici ; brown root rot ; corky root ; grey sterile fungus ; resistance ; inheritance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Tomato accessions (Lycopersicon sp.), along with commercial cultivars and breeding lines were grown in a field infested with the brown root rot (BRR) organism, Pyrenochaeta lycopersici and evaluated for resistance. Three L. esculentum Mill. accessions, P.I. 260397, P.I. 262906 and P.I. 203231, were resistant and were used as male parents in crosses designed to transfer resistance to tomatoes of fresh market type. Through analysis of parental generations and F1 and F2 progenies from three crosses the heritability of resistance in the broad sense was estimated to range from 25 to 43 percent. The minimum number of genes influencing resistance was estimated to be from 4 to 8.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00039121
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