Studies on 60Co gamma irradiation for inducing in vitro mutagenesis in gerbera

In vitro shoots of gerbera 'Regiko' and 'South Pacific' were irradiated with 10, 20 and 30 Gy Co-60 gamma rays (100 Gy/min.) and sub-cultured for two cycles. After rooting in vitro plants were hardened and later transferred in pots for survival and morphological analysis. LD50 value for in vitro shoots in both cultivars was around 20 Gy. 30 Gy irradiation dose severely impaired proliferation and shoot yield in two in vitro cycles. Around 55% shoots initially irradiated with 30 Gy dose were able to root in comparison to above 80% in 20 Gy irradiated shoots. However, plants raised from 20 and 30 Gy irradiated shoots survived equally well in the field. Differences in leaf area and number under 20 and 30 Gy doses after 8 weeks of growth in pots were marginal. Stomata size and number mm(-2) was significantly reduced in plants raised from 30 Gy irradiated shoots. Under 20 Gy dose mutation frequency calculated on the basis of stomata number mm-2 was close to 0.50 in both cultivars, whereas it was above 0.60 with 30 Gy dose. In the present study estimation of mutation frequency on the basis of changes in stomata number per unit area offers an alternative way to assess effects of gamma irradiation even before the appearance of flowers.