X-Rays as a Tool for Inducing Variants of Calibrachoa

The induction of mutations in the plant genome is an alternative method for breeding besides hybridization and transgenesis. This method can generate variation very quickly and decrease the time of the breeding process. The objective of the study was to evaluate two treatments using X-rays as a mutagenic agent in a selected clone of Calibrachoa (Solanaceae). This genus is South American with 11 native species in Argentina (Stehmann, 1999) and it has been recently introduced in the floricultural market. The Floriculture Institute (INTA-Castelar, Argentina) has initiated a breeding program with the aim to obtain agamic compact plants adapted to regional conditions. For this purpose, rooted cuttings (n=30) of a selected Calibrachoa material were irradiated with incremental doses and the LD50 was estimated for 24 Gy. Following these preliminary studies, rooted cuttings were exposed to: a) 1 irradiation event (24 Gy; acute dose) and b) 3 irradiation events (8Gy/week; fractionated dose). The highest number of mutants was obtained with 3 exposure irradiation, thus the fractionated dose treatment was more effective than the acute dose treatment. We obtained mutants in colour and form in Calibrachoa flowers and a novel phenotype with ornamental aptitude for the ornamental market.