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  • 1
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Biochimie 75 (1993), S. 547-554 
    ISSN: 0300-9084
    Keywords: African cassava mosaic virus ; epidemiology ; geminiviruses ; okra leaf curl virus ; tobacco leaf curl virus ; whitefly
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-2242
    Keywords: Key words Rice yellow mottle virus ; Disease resistance ; Plant morphology ; Quantitative trait locus ; Mapping
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  Rice yellow mottle virus (RYMV) resistance QTLs were mapped in a doubled-haploid population of rice, ‘IR64/Azucena’. Disease impact on plant morphology and development, expression of symptoms and virus content were evaluated in field conditions. Virus content was also assessed in a growth chamber. RYMV resistance was found to be under a polygenic determinism, and 15 QTLs were detected on seven chromosomal fragments. For all of the resistance QTLs detected, the favourable allele was provided by the resistant parent ‘Azucena’. Three regions were determined using different resistance parameters and in two environments. On chromosome 12, a QTL of resistance that had already been detected in this population and another indica/japonica population was confirmed both in the field and under controlled conditions. Significant correlations were observed between resistance and tillering ability, as measured on control non-inoculated plants. In addition, the three genomic fragments involved in resistance were also involved in plant architecture and development. In particular, the semi-dwarfing gene sd-1, on chromosome 1, provided by the susceptible parent, ‘IR64’, mapped in a region where resistance QTLs were detected with most of the resistance parameters. In contrast, the QTL of resistance mapped on chromosome 12 was found to be independent of plant morphology.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1432-2242
    Keywords: Key words QTL ; Complementary epistasis ; Marker-assisted selection ; Quantitative resistance ; Rice yellow mottle virus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  The genetic basis of resistance to rice yellow mottle virus (RYMV) was studied in a doubled-haploid (DH) population derived from a cross between the very susceptible indica variety ‘IR64’ and the resistant upland japonica variety Azucena. As a quantitative trait locus (QTL) involved in virus content estimated with an ELISA test has been previously identified on chromosome 12, we performed a wide search for interactions between this QTL and the rest of the genome, and between this QTL and morphological traits segregating in the population. Multiple regression with all identified genetic factors was used to validate the interactions. Significant epistasis accounting for a major part of the total genetic variation was observed. A complementary epistasis between the QTL located on chromosome 12 and a QTL located on chromosome 7 could be the major genetic factor controlling the virus content. Resistance was also affected by a morphology-dependent mechanism since tillering was interfering with the resistance mechanism conditioned by the epistasis between the two QTLs. Marker-assisted backcross breeding was developed to introgress the QTLs of chromosome 7 and chromosome 12 in the susceptible ‘IR64’ genetic background. First results confirmed that if both QTLs do not segregate in a backcross-derived F2 population, then the QTL of chromosome 12 cannot explain differences in virus content. A near-isogenic line (NIL) approach is currently being developed to confirm the proposed genetic model of resistance to RYMV.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Integrated pest management reviews 3 (1998), S. 209-224 
    ISSN: 1572-9745
    Keywords: cassava ; Manihot esculenta ; Africa ; cassava mosaic virus disease ; whitefly vector (Bemisia tabaci) ; control ; varietal diversity ; resistance ; deployment ; durability ; breakdown ; phytosanitation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Cassava mosaic virus disease (CMD) is prevalent and causes serious losses in cassava (Manihot esculenta) in southern India and in many parts of sub-Saharan Africa. The disease is caused by viruses of the Geminiviridae that are transmitted by the whitefly Bemisia tabaci and disseminated in the stem cuttings used routinely for propagation. The main approach to control is through the use of virus-resistant varieties, but suitable ones are not always available and susceptible varieties are still widely grown. This explains why CMD continues to be a problem in many areas. CMD-resistant varieties have several features which are considered in this review:- • They are not readily infected, even when exposed to large amounts of vector-borne inoculum. • When infected they develop symptoms that tend to be inconspicuous and not associated with obvious deleterious effects on growth or yield. Moreover, the symptoms become even less conspicuous as growth proceeds and plants may eventually recover and become symptomless. • Infected plants support a low virus content and they are likely to be a poor source of inoculum from which further spread can occur. • Virus is not fully systemic within infected plants which can be a source of uninfected planting material when stem cuttings are collected for further propagation. This phenomenon is referred to as ‘reversion’ and it has an important ‘cleansing effect’ in restricting or preventing the progressive deterioration in health status that would otherwise occur during successive cycles of vegetative propagation. The available information on the different components of resistance is discussed and it is concluded that they are inter-related features of the same basic mechanism that restricts virus entry, replication and movement within the host. It is argued that the effectiveness and durability of virus-resistant varieties are likely to be influenced by the way in which they are deployed. However, this topic has received little attention from researchers and there is continuing uncertainty on the effects of CMD on the yield of resistant varieties and on the role of phytosanitation. This involves the use of virus-free planting material and the removal (roguing) of any additional diseased plants that occur. Some consider that these procedures complement the use of virus-resistant varieties and should be adopted, whereas others argue that they are unnecessary and inappropriate. It is concluded that there is considerable scope for utilizing resistant varieties more widely and more effectively than at present, but in doing so it is important to avoid eroding the genetic diversity that is currently such a marked feature of cassava cultivation in Africa.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    European journal of plant pathology 102 (1996), S. 645-654 
    ISSN: 1573-8469
    Keywords: epidemiology ; geminivirus ; integrated pest management ; whitefly ; yield losses
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Components of resistance of cassava (Manihot esculenta) to African cassava mosaic virus (ACMV) and their interrelationships were confirmed and quantified in a series of experiments at Adiopodoumé (Ivory Coast, West-Africa). The response to virus infection and toBemisia tabaci infestation of a large collection of cassava, including local cultivars and others derived from inter-specificM. glaziovii hybrids was assessed. A consistent correlation was found between virus titre, symptom intensity, disease incidence and non-systemicity (recovery) which suggests that they are different expressions of the same genetic resistance. By contrast, there was no correlation between whitefly infestation and incidence of ACMV, suggesting that resistance to virus and vector are determined by two distinct genetic mechanisms. Several improved cultivars derived from inter-crossing cassava withM. glaziovii as well as some local cultivars were highly resistant and combined low susceptibility, low symptom intensity, low virus content and high level of recovery. Although yield losses ranged from 10% to 30% in such resistant cultivars, the combined effect of high field resistance and high rate of recovery lead to low disease incidence and limited yield losses, even in areas of high infection pressure such as Adiopodoumé.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1573-8469
    Keywords: Africa ; serotype ; virus diversity and distribution ; strain competition
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Serological variability of isolates of rice yellow mottle virus (RYMV) collected in Côte d'Ivoire was assessed by immunological tests with polyclonal and monoclonal antibodies (MAbs). Two serotypes (named S1 and S2) were distinguished. The S1 isolates had common epitopes which were absent in S2 isolates, whereas they lacked epitopes shared by S2 isolates. There was no evidence of S1 and S2 mixtures, although S1 and S2 isolates were sometimes found in nearby sites. Serotype S2 was more prevalent in Côte d'Ivoire than S1, and was in a large majority in the centre and the south of the country. By contrast, S1 occurred more widely in the north. S1 isolates were also found in neighbouring countries at the north of Côte d'Ivoire. In tests with monoclonal antibodies, three additional serotypes were found, one in West-Africa and two in East-Africa. Using the primers developed against an S2 isolate from Côte d'Ivoire, all S2 but not the S1 isolates were transcribed and amplified by RT-PCR, and another set of primers was developed to amplify S1 isolates. S1 and S2 have different biological properties, and competition between isolates of the two strains was apparent resulting in S2 dominance over S1. This was assessed using S1 and S2 strain specific MAbs, and it occurred whatever the pattern of inoculation or the rice variety tested. Differences in pathogenicity and virus titre did not account for strain competition, as there was no relation between symptom severity, virus content and serotype of the isolates in Oryza sativa indica cultivars.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1573-8469
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Type of Medium: Electronic Resource
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  • 8
    Publication Date: 1994-01-01
    Print ISSN: 0249-5627
    Electronic ISSN: 1297-9643
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Published by EDP Sciences
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  • 9
    Publication Date: 2006-09-01
    Description: Abstract  An appreciation of the risks caused by emergent plant viruses is critical in tropical areas that rely heavily on agriculture for subsistence and rural livelihood. Molecular ecology, within 10 years, has unraveled the factors responsible for the emergence of several of the economically most important tropical plant viruses: Rice yellow mottle virus (RYMV), Cassava mosaic geminiviruses (CMGs), Maize streak virus (MSV), and Banana streak virus (BSV). A large range of mechanisms—most unsuspected until recently—were involved: recombination and synergism between virus species, new vector biotypes, genome integration of the virus, host adaptation, and long-distance dispersal. A complex chain of molecular and ecological events resulted in novel virus-vector-plant-environment interactions that led to virus emergence. It invariably involved a major agricultural change: crop introduction, cultural intensification, germplasm movement, and new genotypes. A current challenge is now to complement the analysis of the causes by an assessment of the risks of emergence. Recent attempts to assess the risks of emergence of virulent virus strains are described.
    Print ISSN: 0066-4286
    Electronic ISSN: 1545-2107
    Topics: Biology , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Published by Annual Reviews
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