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  • 2020-2022
  • 1990-1994  (4)
  • 1994  (4)
  • 1
    ISSN: 1432-2242
    Keywords: Complementation ; Granule-bound starch synthase ; Amylose content ; Gene expression ; Inheritance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Granule-bound starch synthase (GBSS) catalyses the synthesis of amylose in starch granules. Transformation of a diploid amylose-free (amf) potato mutant with the gene encoding GBSS leads to the restoration of amylose synthesis. Transformants were obtained which had wild-type levels of both GBSS activity and amylose content. It proved to be difficult to increase the amylose content above that of the wild-type potato by the introduction of additional copies of the wild-type GBSS gene. Staining of starch with iodine was suitable for investigating the degree of expression of the inserted GBSS gene in transgenic amf plants. Of the 19 investigated transformants, four had only red-staining starch in tubers indicating that no complementation of the amf mutation had occured. Fifteen complemented transformants had only blue-staining starch in tubers or tubers of different staining categories (blue, mixed and red), caused either by full or partial expression of the inserted gene. Complementation was also found in the microspores. The segregation of blue- and red-staining microspores was used to analyse the inheritance of the introduced GBSS genes. A comparison of the results from microspore staining and Southern hybridisation indicated that, in three tetraploid transgenics, the gene was probably inserted before (duplex), and in all others after, chromosome doubling (simplex). The partial complementation was not due to methylation of the HPAII/MSPI site in the promoter region. Partially complemented plants had low levels of mRNA as was found when the GBSS expression levels were inhibited by anti-sense technology.
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  • 2
    ISSN: 1432-2242
    Keywords: Protoplast fusion ; Potato ; Tomato ; Post-fertilisation barriers ; Introgression
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Somatic fusion hybrids between the diploid potato and tomato were backcrossed to several genotypes of potato. Two ploidy levels of fusion hybrids, 4x and 6x, were used as female parents in backcrosses with five clones of 4x-potato. An estimate of the berry set and “seed set” in immature berries harvested 14–21 days after pollination indicated that crosses between certain combinations of 6x-fusion hybrids and male parents were more successful than others. The culture of over 4000 young seeds from berries harvested 2–2.5 weeks after pollination gave rise to a single seedling, 93.6701, from the cross between the 6x-fusion hybrid C 31-17-1 and the 4x-potato AM 66.42. This seedling was found to possess a pentaploid chromosome number, which was expected of a 6x × 4x cross. Isozyme analysis and DNA hybridisation studies confirmed that the seedling 93.6701 was indeed a backcross (BC1) progeny. Morphologically, this BC1 plant resembled potato with respect to plant habit, leaf shape, stolons and tuber characteristics, while some of the characters, such as floral morphology and the fragrance of the crushed leaves (typical of tomato), were intermediate. It was male sterile but could be successfully hybridized with 4x-potato through in vitro culture of yound seeds; thus, BC2 plants were obtained. The possibilities of backcrossing and the potential use of BC1 and BC2 plants in genetics and breeding are discussed.
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  • 3
    ISSN: 1617-4623
    Keywords: Potato ; Solanum tuberosum ; Phytophthora infestans ; RFLP ; R genes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Phytophthora infestans (Mont.) de Bary is the most important fungal pathogen of the potato (Solanum tuberosum). The introduction of major genes for resistance from the wild species S. demissum into potato cultivars is the earliest example of breeding for resistance using wild germplasm in this crop. Eleven resistance alleles (R genes) are known, differing in the recognition of corresponding avirulence alleles of the fungus. The number of R loci, their positions on the genetic map and the allelic relationships between different R variants are not known, except that the R1 locus has been mapped to potato chromosome V The objective of this work was the further genetic analysis of different R alleles in potato. Tetraploid potato cultivars carrying R alleles were reduced to the diploid level by inducing haploid parthenogenetic development of 2n female gametes. Of the 157 isolated primary dihaploids, 7 set seeds and carried the resistance alleles R1, R3 and R10 either individually or in combinations. Independent segregation of the dominant R1 and R3 alleles was demonstrated in two F1 populations of crosses among a dihaploid clone carrying R1 plus R3 and susceptible pollinators. Distorted segregation in favour of susceptibility was found for the R3 allele in 15 of 18 F1 populations analysed, whereas the RI allele segregated with a 1:1 ratio as expected in five F1 populations. The mode of inheritance of the R10 allele could not be deduced as only very few F1 hybrids bearing R10 were obtained. Linkage analysis in two F1 populations between R1, R3 and RFLP markers of known position on the potato RFLP maps confirmed the position of the R1 locus on chromosome V and localized the second locus, R3, to a distal position on chromdsome XI.
    Type of Medium: Electronic Resource
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  • 4
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