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  • Disease resistance  (2)
  • Reversion to fertility  (2)
  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Theoretical and applied genetics 74 (1987), S. 601-609 
    ISSN: 1432-2242
    Keywords: Cytoplasmic male-sterility (cms) ; Reversion to fertility ; Mitochondrial DNA ; Maize ; Somaclonal variation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Plants were regenerated from callus cultures of maize inbred W182BN with the S(USDA) type of cytoplasmic male sterility (cms). Some regenerates from 16 of 18 separate cultures had fertile tassels. Many other regenerates, whose fertility could not be scored accurately because of abnormal plant morphology, produced fertile progeny after pollination with N cytoplasm W182BN. Revertant plants and/or progeny were obtained from all 18 cultures, which included the CA, D, LBN, and S sources of cmsS. More revertants were recovered from cultures maintained as callus for 12 months than from 3–4 month old cultures. Several types of evidence (absence of segregation for fertility after selfing or pollination of revertants with standard W182BN, pollen viability counts, failure of revertants to restore sterile cmsS lines to fertility, mitochondrial DNA analyses) indicated that the reversion to fertility involved cytoplasmic rather than nuclear alterations. All revertants examined lacked the S1 and S2 plasmid-like DNAs characteristic of the mitochondrial genome of sterile cmsS lines. Most callus cultures lost S1 and S2 after 13–20 months in vitro. No revertants were seen among thousands of W182BN cmsS plants grown from seed in the field or among plants from tissue cultures of W182BN with the C or T types of cms. The cytoplasmic revertants recovered from culture may be useful for the molecular analysis of cmsS.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-2242
    Keywords: S-type cytoplasmic male sterility ; Reversion to fertility ; Mitochondrial genome organization ; Recombination ; Maize
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The mitochondrial genome organizations of a number of independent culture-derived fertile CMS-S revertants with the nuclear genotype W182BN were compared to spontaneous field revertants with the genotypes WF9, M825/Oh07 and 38-11. Regions of the genome around sequences homologous to the terminal repeats of the linear S1 and S2 episomes characteristic of CMS-S mitochondria were used as hybridization probes on Southern blots of BamHI and SalI digested mitochondrial DNA. The results obtained suggest that the nuclear, not the cytoplasmic, genotype of the parent plant affects the type of novel mitochondrial DNA organization found in the revertant. The DNA reorganization during reversion from CMS-S in tissue culture appears to be similar to that observed in spontaneous revertants obtained during the normal plant life-cycle. Unlike the situation for reversion from CMS-T, no common DNA sequence or reading frame appeared to be lost or disrupted in revertants.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Theoretical and applied genetics 91 (1995), S. 1293-1300 
    ISSN: 1432-2242
    Keywords: Somatic hybridization ; Black rot ; Disease resistance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Black rot caused by the bacterium Xanthomonas campestris pv campestris is one of the most serious diseases of Brassica oleracea. Since sources of resistance to the disease within B. oleracea are insufficient and control means are limited, the development of resistant breeding lines is extremely desirable. Certain lines of B. napus contain very high resistance controlled by a dominant gene, but crossing the two species sexually is very difficult. Therefore, somatic hybrids were produced by protoplast fusion between rapid cycling B. oleracea and a B. napus line highly resistant to X. campestris pv campestris. Hybrid identity was confirmed by morphological studies, flow cytometric estimation of nuclear DNA content, and analysis of random amplified polymorphic DNA (RAPD). Inoculations with the pathogen identified four somatic hybrids with high resistance. The resistant hybrid plants were fertile and set seed when selfed or crossed reciprocally to the bridge line ‘15’ (Quazi 1988). Direct crosses to B. oleracea were unsuccessful, but embryo rescue facilitated the production of a first-backcross generation. The BC1 plants were resistant to the pathogen. Progeny from the crosses to ‘line 15’ were all susceptible. Embryo rescue techniques were not obligatory for the development of a second-backcross generation, and several resistant BC2 plants were obtained.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Theoretical and applied genetics 100 (2000), S. 810-819 
    ISSN: 1432-2242
    Keywords: Key words Bacterial soft rot ; Disease resistance ; Chinese cabbage ; Protoplast fusion ; Brassica rapa ; B. oleracea ; B. napus ; Erwinia carotovora subsp. carotovora
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  Erwinia soft rot is a destructive disease of Brassica rapa vegetables. Reliable sources of resistance and control methods are limited, so development of highly resistant breeding lines is desirable. Protoplasts from B. rapa and B. oleracea genotypes selected for resistance to soft rot were fused in order to combine different sources of resistance. Twelve somatic hybrids (synthetic B. napus) were obtained and confirmed by morphology, nuclear DNA content, and RAPD analysis. They were normal looking plants that easily set seeds following self-pollination and backcrossing to B. rapa. Assays of detached leaves or seedlings inoculated in a mist-chamber showed that most somatic hybrids had lower disease severity ratings than the B. rapa fusion partner and a commercial variety of B. napus. Some progeny from selfing or backcrossing of somatic hybrids to B. rapa showed much more resistance than either fusion partner. The offspring populations of the somatic hybrids (F1–S1 and F1–BC1) clearly moved to the resistant direction compared to the parents; the percentage of resistant plants increased from 21% (average of parents) to 36% (F1–S1) and 48% (F1–BC1). These results suggest that it may be possible to obtain highly resistant B. rapa lines by further backcrossing and selection.
    Type of Medium: Electronic Resource
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