Gerbera jamesonii ‘Super Gerbera’ explants were irradiated in vitro with 60Co γ-rays (8–100 Gy). Some received a single dose, while others received two or three at successive multiplication cycles. Several parameters were measured after 6 weeks of in vitro culture, to compare the effects of irradiation on haploid and diploid clones. Productivity is linked to the ploidy level, whereas total growth is not. Total growth inhibition is proportionate to the given dose. Callus and plantlet growth are either inhibited or stimulated, depending on the type of treatment. Callus growth is stimulated by low doses, which induce the transformation of apices into calli; treatment of successive cycles with low doses (20 and 30 Gy for diploids, 10 and 15 Gy for haploids) ensures better plantlet development. High doses inhibited growth of calli and plantlets up to the 50% level. Variations in morphology and in chlorophyll and anthocyanin content were observed among haploid and diploid irradiated explants. Plantlet production is a good criterion for an overall evaluation. Optimal dosage to ensure 50% growth and multiplication rates is estimated at 26 Gy for diploid clones and 16 Gy for haploid clones.