Production of compact petunias through polyploidization

Petunia, a commercially important ornamental plant worldwide, has been subjected to breeding programs that have yielded a high number of varieties. One of the key factors in the commercial value of these varieties is plant compactness. Currently, compact petunias are obtained through the application of expensive, harmful and shortlasting chemicals. To avoid the use of these chemicals, transgenic plants that over-express dwarf-inducing genes have been recently proposed as an alternative, but the current legislation regarding transgenic plants restricts their commercialization. In this work, we studied the effect of polyploidization in the plant architecture of Petunia axillaris, an Argentine native petunia. We developed a new polyploidization protocol that consisted in culturing petunia leaves in RL medium (MS medium supplemented with 30 g l(-1) sucrose, 1 mg l(-1) BA and 0.2 mg l(-1) IAA) supplemented with 0.2 g l(-1) colchicine for 15 days. This protocol allowed the regeneration of stable autotetraploid petunias (polyploidization rate: 29.0 +/- 8,2%), which were 54% more compact than the diploid ones. Furthermore, they exhibited no variations in agronomical traits compared to the initial genotypes, except for a short delay in blooming. These autotetraploid plants can be used in different breeding programs and the polyploidization method developed can be tested in others cultivars of the genus Petunia for the same purpose.