Aberrant Cytological Behavoir in Tobacco Androgenic Doubled Haploid ✕ Parental Cultivar Hybrids

Abstract

Amplication of DNA has been reported for another culture‐derived doubled haploid (DH) lines of tobacco (Nicotiana tabacum L.). The purpose of this study was to evaluate the cytological changes associated with this DNA amplification. Crosses were made between three second‐cycle DHs and their source cultivars, NC95 and C139. Examination of chromosome pairing in pollen mother cells (PMCs) revealed that two of the hybrids produced a single quadrivalent at metaphase I, whereas the other hybrid formed two quadrivalents. In all of the hybrids, quadrivalents either were in a ring, or consisted of two ring bivalents connected by a single strand of chromatin. This latter form, which was termed a side‐arm quadrivalent, appears to represent pairing between amplified homologous chromosome regions in nonhomologous chromosomes. These findings suggest that at least some of the DNA that is amplified in tobacco DHs is present in large blocks, and occurs in identical or similar sequences located on different chromosome pairs. Observations of chromosome and spindle behavior in somatic anaphases and meiotic anaphase I and tetrad cells revealed the presence of a low frequency of spindle errors in the hybrids. while the genotypic effectofr the frequency of abnormal mitotic anaphases was not significant, a highly significant genotypic effect was found fot the frequency of abnormal anaphase I cells. All hybrids had significantly more anaphase I errors than did their parental lines. These spindle errors may be caused by the amplification of specific sequences within the DH lines or by the differences between the parental lines in amount of DNA.