Effects of 60Co gamma rays on Gerbera jamesonii plantlets irradiated in vitro

The aim of this work was to determine the direct inhibitory effects of 60 γ-rays on plantlets and to control them in a future program of experimental mutagenesis. Gerbera jamesonii plantlets were irradiated in vitro using two sources of 60Co γ-rays. The following variables were tested: dose rate, total dose, irradiation of growth medium, time interval between the exposure to γ-rays and the subdivision and transfer to fresh medium, and dose fractionation. These variables were evaluated using regeneration rate of new shoots, callus production, and plantlet growth rate (fresh weight). The optimal dose ranged around 50 Gy at a low dose rate (8.4 Gy · h-1) and 30 Gy at high dose rate (600 Gy · h-1). These conditions assured minimal development of callus and 50% of the normal multiplication rate. The γ-irradiation may be done during a 1-week interval before or after transfer on fresh medium, without causing any additional effects. Interrupted doses (3 x 10 Gy at 48-h intervals) caused less important inhibitory effects than a single dose (30 Gy), but the intensity of the reaction varied according to clone and the measured parameter. The clone 'Duplex' reacted favourably; this type of treatment ensured better callus and plantlet growth and a higher rate of regeneration. In the case of 'Mardi Gras', which is less sensitive to fractionated doses, only the weight of the plantlets was significantly less reduced