Characterization of interspecific hybrids of <i>Petunia</i> and <i>Calibrachoa</i> by multiplex PCR, DNA content, and chromosome number

<p><i>Petunia</i> and <i>Calibrachoa</i> are ornamental plants of worldwide economic importance. Commercially, it is useful to combine desirable characteristics of <i>Calibrachoa</i>, including the large diversity of flower colors, with the pH tolerance and vigorous growth of <i>Petunia</i>. For investigation of interspecific hybrids between <i>Petunia</i> and <i>Calibrachoa</i> we used four different introns with flanking exon areas, each from a different gene and with a different sequence for <i>Petunia</i> and <i>Calibrachoa</i>, as genus-specific markers for chromosomes in interspecific hybrids. PCR primers specific for <i>Petunia</i> and <i>Calabrachoa</i> were made from the determined sequences and tested on a range of presumed hybrids using multiplex PCR, which confirmed that the hybrids were derived from these two species. Flow cytometry demonstrated that the hybrids were triploid, and determination of chromosome numbers showed that two of the chromosome sets were from <i>Calibrachoa</i>, i.e. that the other parent, <i>Petunia</i>, was diploid. Similar methods can be used for molecular characterization of other new hybrids made between closely related species or cultivars.</p