Basis and extent of genetic variability among doubled haploid plants obtained by pollen culture in Nicotiana sylvestris

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Abstract
All diploid plants (doubled-haploid plants: D.H.) regenerated by androgenesis from binucleated pollen grains in Nicotiana sylvestris differ genetically from the original line as far as morphological features and growth rates are concerned. This androgenic variation (A.V.) is under nuclear control and is transmitted continuously by some D.H. for at least four generations of selfing; other D.H. progenies segregate. Further androgeneses carried out on one single D.H. reveal a new variability and increase the drift from the original line. All results cannot be explained by the presence of residual heterozygosity in the original line, and we suggest that most of the A.V. could originate from changes that occur in the DNA of the vegetative pollen grain cell. D.H. resulting from endomitosis of the vegetative cell would be ‘homozygous’ and stable, whereas D.H. resulting from nuclear fusion between a vegetative and a generative cell would be ‘heterozygous’ and would segregate in seeds through succeeding generations.