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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Theoretical and applied genetics 92 (1996), S. 425-435 
    ISSN: 1432-2242
    Keywords: Key words  RFLP ; Molecular markers ; Fruit breeding
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract   Studies on the nature of restriction fragment length polymorphisms (RFLPs) were undertaken to characterize the Citrus genome. This type of analysis has not been carried out with any other perennial crop. Citrus reticulata Blanco cv Clementine, C. xparadisi Macf. cv Duncan, and an F1 hybrid (LB 1-21) were used to determine what probe/enzyme combinations revealed polymorphisms in Southern analysis, and a backcross family (LB 1-21×`Clementine') of 65 randomly selected hybrid seedlings was used for some analyses. A majority (73%) of the clones examined from a PstI genomic library appeared to detect single-copy sequences based on RFLP banding patterns, while clones from a cDNA library revealed a lower percentage of single copy sequences. When hybridization stringencies were lowered, 21% of the genomic clones examined revealed greater copy numbers. PstI digestion of `Duncan' DNA indicated abundant methylation, so the relatively high frequency of multiple-copy sequences observed at moderate stringency cannot be attributed to a lack of methylation of the Citrus DNA. The polymorphisms in banding patterns observed primarily resulted from insertions and/or deletions rather than from base substitutions, and a model is presented to account for the varying patterns obtained from individual probes with different restriction enzymes. Finally, a model for transposon activity in Citrus is proposed, based on observations made during the course of these studies.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-2242
    Keywords: Key words  Citrus cultivar improvement ; Germ plasm expansion ; Protoplast fusion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract   We have developed an efficient protoplast-fusion method to produce somatic hybrid allopolyploid plants that combine Citrus with seven related genera, including four that are sexually incompatible. In this paper we report the creation of 18 new allotetraploid hybrids of Citrus, including ten among sexually incompatible related genera, that may have direct cultivar potential as improved citrus rootstocks. All hybrids were confirmed by cytological and RAPD analyses. If fertile, the attributes of these hybrids may be amenable to further genetic manipulation by breeding at the tetraploid level. Wide somatic hybridization of Citrus via protoplast fusion bypasses biological barriers to the natural allopolyploidization of Citrus, and creates new evolutionary opportunities that would be difficult or impossible to achieve by natural or conventional hybridization.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Theoretical and applied genetics 92 (1996), S. 688-695 
    ISSN: 1432-2242
    Keywords: Key words Citrus L. ; Poncirus trifoliata L. ; Random amplified polymorphic DNA ; Bulked segregant analysis ; Genome mapping
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  A localized genetic linkage map was developed of the region surrounding the citrus tristeza virus (CTV) resistance gene (designated Ctv) from Poncirus trifoliata L., a sexually compatible Citrus relative. Bulked segregant analysis (BSA) was used to identify potential resistance-associated RAPD fragment markers in four intergeneric backcross families that were segregating for CTV resistance. Eight RAPD fragments were found that were consistently linked to Ctv in the four families. Map distances and locus order were determined with MAPMAKER 3.0, using the results obtained from 59 individuals in the largest family. Also, a consensus map was constructed with JOINMAP 1.3, using pooled results from the four backcross families. Marker orders were identical, except for 1 marker, on these independently developed maps. Family-specific resistance-associated markers were also identified, as were numerous susceptibility-associated markers. The identification of markers tightly linked to Ctv will enable citrus breeders to identify plants likely to be CTV-resistant by indirect, marker-assisted selection, rather than by labor-intensive direct challenge with the pathogen. These markers also provide a basis for future efforts to isolate Ctv for subsequent genetic manipulation.
    Type of Medium: Electronic Resource
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