Standardisation of Gamma Dose in Papaya cv. Ranchi Local and Arka Surya

Abstract

Gamma radiation is the most commonly used mutagen in plants as it causes a high frequency of induced mutations. It can be used to overcome the difficulties in papaya breeding to get true to type plantlets especially in dioecious varieties. An optimum dose is highly desired to produce the high frequency of mutations with minimum killing of treated individuals. Therefore, the present investigation was undertaken to determine the LD50 of gamma rays and effect of different dosages of gamma rays on morphological, physiochemical, biochemical parameters of papaya. In the preliminary dosimetry study, seeds from two papaya varieties, Ranchi Local and Arka Surya were irradiated in a gamma chamber at Bhabha Atomic Research Centre (BARC), Mumbai with 7 different radiation doses ranging from 10 Gy to 70 Gy at every interval of 10 Gy. Prior to irradiation in one experiment, seeds were soaked overnight in water and surface-dried and in another experiment, seeds were immersed in water while irradiation. Radio sensitivity test of germinated seeds showed that the LD50 value was 28.35 and 33.13 Gy for pre-soaked seeds & 24.05 and 23.78 Gy for seeds immersed in water for Ranchi Local & Arka Surya variety respectively. The GR50 was thus calculated to be 31.64 and 37.50 Gy for presoaked seeds & 28.28 and 30.11 Gy for seeds immersed in water for Ranchi Local & Arka Surya variety respectively. From the analysis of GR50 for both the irradiated conditions, it was found that 30 Gy (for pre-soaked seeds) and 20 Gy (for seeds immersed in water) was the most effective dose with maximum possibility of desirable mutation.