Cytological Evaluation of Tobacco Doubled Haploids for Presence of Amplified Homologous Chromosomal Regions
Atypical quadrivalents, resulting from pairing between homologous amplified chromosome segments, have been observed in hybrids between low-yielding, second-cycle doubled haploid (DH) lines of tobacco (Nicotiana tabacum L.) and their source cultivars. The first objective of this study was to determine if homologous amplified chromosome segments are present in other DHs, such as those that have been through only one cycle of anther culture and those that are only moderately depressed in yield. The second objective was to trace the development of amplified chromosomal regions through consecutive cycles of anther culture. Chromosome pairing was studied in DH × cultivar hybrids involving high- and low-yielding first-cycle DHs and second-cycle DHs derived from the high-yielding first-cycle DHs. There appeared to be no correlation between multivalent formation and yield. The one DH that was found to contain homologous amplified chromosome segments was a low-yielding first-cycle DH, NC95 DHL. NC95 DHL was then crossed to two second-cycle DHs derived from it that had previously been determined to have homologous amplified chromosome segments. Cytological analysis of these DH × DH hybrids indicated that the amplified chromosomes in NC95 DHL passed unchanged to one of its second-cycle derivatives. In contrast, a number of modifications occurred in another of its derivatives during the second cycle of anther culture.
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