A simple method of chromosome doubling using colchicine in Torenia (Linderniaceae), and the behavior of meiotic chromosomes in amphidiploids

Although Torenia fournieri (Linderniaceae) and Torenia baillonii carry 2n=18 and 2n=16 chromosomes, respectively, their F1 hybrid showed eight bivalent chromosomes with chiasmata as a result of interspecific pairing and one univalent chromosome from T. fournieri. To elucidate the behavior of the chromosomes in the amphidiploids, we developed a simple method of chromosome doubling by the application of colchicine combined with the induction of adventitious buds in detached leaves. The frequency of polyploid plants was highest (8%) in the treatment with 15 μmol mol colchicine for 2 days. The meiocytes of the amphidiploids showed extent pairing (i.e., the appearance of bivalent and multivalent chromosomes), including intraspecific and interspecific pairings. This result supports the hypothesis that T. fournieri and T. baillonii have eight homologous chromosomes and that T. fournieri possesses an extra chromosome of unknown origin.