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  • 1
    ISSN: 1432-2242
    Keywords: Tomato ; Lycopersicon esculentum ; Root knot nematode resistance ; Meloidogyne ; RFLP markers
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The Mi gene originating from the wild tomato species Lycopersicon peruvianum confers resistance to all major root knot nematodes (Meloidogyne spp.). This single dominant gene is located on chromosome 6 and is very closely linked to the acid phosphatase-1 (Aps-1) locus. Resistance to nematodes has been introgressed into various cultivars of the cultivated tomato (L. esculentum), in many cultivars along with the linked L. peruvianum Aps-1 1 allele. By using a pair of nearly isogenic lines differing in a small chromosomal region containing the Mi and Aps-1 loci, we have identified two RFLP markers, GP79 and H6A2c2, which are located in the introgressed L. peruvianum region. Analysis of a test panel of 51 L. esculentum genotypes of various origins indicated that GP79 is very tightly linked to the Mi gene and allows both homozygous and heterozygous nematode-resistant genotypes to be distinguished from susceptible genotypes, irrespective of their Aps-1 alleles. Marker H6A2c2 is linked to the Aps-1 locus and is capable of discriminating between the L. peruvianum Aps-1 1 allele and the L. esculentum Aps-1 3 and Aps-1 + alleles. In combination, these RFLP markers may provide a powerful tool in breeding tomatoes for nematode resistance.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-2242
    Keywords: Molecular markers ; Sex differences in recombination
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract In order to map genes determining resistance to bacterial canker in tomato, backcrosses were made between a resistant and a susceptible Lycopersicon peruvianum accession. The linkage study with RFLP markers yielded a genetic map of L. Peruvianum. This map was compared to that derived from a L. esculentum x L. pennellii F2 population, based on 70 shared RFLP markers. The maps showed a good resemblance in both the order of markers and the length of the chromosomes, with the exception of just one relocated marker on chromosome 9. Because backcrosses were made with the F1, either as the pollen parent or as the pistil parent, linkage maps from male and female meioses could be estimated. It was concluded that recombination at male meiosis was reduced, and that gametophytic selection for parental genotypes at more than one locus per chromosome might be partly responsible for the reduction of the estimated male map length.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1432-2242
    Keywords: Lycopersicon esculentum ; RFLP ; Resistance gene mapping ; Cladosporium fulvum ; Genetic variation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The contribution of introgressed regions derived from wild species to the genetic variation within the species of Lycopersicon esculentum was investigated by comparing the RFLP patterns of 2 introgression-free, obsolete cultivars (‘Moneymaker’ and ‘Premier’) and a modern cultivar (‘Sonatine’) that carries at least 5 introgressed resistance genes. In this analysis 195 mapped nuclear markers were used in combination with 6 restriction enzymes. Among the 1170 probe-enzyme combinations tested, only 3 showed a polymorphism between the 2 introgression-free cultivars. On the other hand 24 probe-enzyme combinations were found to exhibit polymorphisms between ‘Moneymaker’ and ‘Sonatine’. These represented ten polymorphic loci distributed among 5 linkage groups on chromosomes 1, 3, 4, 6, and 9. On the assumption that most of the polymorphic loci corresponded to introgressed chromosome segments of wild species carrying resistance genes, linkages between these loci and the component resistance genes were examined by RFLP analysis of pairs of near-isogenic lines differing only for one particular resistance gene, and a variety of commercial cultivars having different resistance gene compositions. Two of the polymorphic linkage groups could thus be ascribed to resistance genes whose map positions were already known: Cf2 on chromosome 6 and Tm2a on chromosome 9, whereas another marker, TG301 on chromosome 1, could be assigned to the Cladosporium fulvum resistance gene Cf9 with a hitherto disputable map position. By linkage analysis of a segregating F2 population the genetic distance between the Cf9 gene and the marker TG301 was estimated at 5.5 ± 2.3 cM.
    Type of Medium: Electronic Resource
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