Methods for Selection of Low-Temperature Tolerant Mutants of Chrysanthemum morifolium Ramat. Using Irradiated Cell Suspension Cultures III. Comparison of Mutants Selected with or without Preselection in vitro at Low-Temperature

One hundred variants of Chrysanthemum morifolium cv. ‘Parliament’, selected on a single plant basis for early flowering at low temperature, were tested on a clonal basis. These variants originated from irradiated or non-irradiated microcalli subjected to a one-step greenhouse selection procedure, or, a two-step selection procedure (preselection in vitro at 6°C followed by selection in the greenhouse). Clones originating from irradiated calli flowered significantly earlier than the controls. Most of the low-temperature tolerant (LTT) mutants were found among plants obtained by the one-step selection procedure. Variants originating from slowly regenerating calli yielded more LTT mutants as compared to those of fast(er) regenerating calli. We therefore conclude that, irradiation and subsequent selection of plants from slowly regenerating calli considerably increases the efficiency of selecting LTT mutants. The expected advantage of a preselection in vitro at low-temperature could not be confirmed.