In vitro colchicine induction of tetraploids inPelargonium rapaceum

The aim of this study was to produce polyploid plants in section Hoarea of Pelargonium as materials for breeding new commercial cultivars with desirable characteristics. We selected Pelargonium rapaceum (section Hoarea) as the starting material. Leaf explants of in vitro plantlets and regenerated diploid calli of P. rapaceum were treated with colchicine at different concentrations for various times, and then cultured in vitro to obtain regenerated plantlets. The DNA ploidy level of individual plants was determined by flow cytometry, and the plants were classified as diploid, mixoploid, or tetraploid. Three putative tetraploid plants were induced when in vitro leaf explants were immersed for 48 h in liquid Murashige and Skoog medium supplemented with 1000 mg L-1 colchicine, and when diploid calli were cultured on Murashige and Skoog medium supplemented with 1 mg L-1 colchicine for 30 days. The putative tetraploid plants were propagated using the same protocol, and their characteristics were evaluated. The guard cells and fertile pollen grains of regenerated plants were significantly larger than those of the original diploid plants. However, the flowers of the regenerated plants were the same size and color as those of the original diploid plants, and the pollen fertility of the regenerated plants was considerably lower than that of original diploid plants. Furthermore, when the regenerated plants were self-pollinated, there was an incomplete fruit and seed set. Consequently, no large flowers were produced by three tetraploid strains. Nevertheless, we propose that the colchicine treatment should be used to induce P. rapaceum tetraploid plants, and anticipate that when many more explants are treated with colchicine at optimal concentrations and times, this will induce tetraploid plants with larger flowers that could be useful for breeding new cultivars in Pelargonium section Hoarea.