Effects of X-irradiation on adventitious bud regeneration from in vitro leaf explants of Rosa hybrida

The effectiveness of X-radiation on regeneration of adventitious buds on in vitro leaf explants of three Rosa hybrida L. genotypes was studied. In vit ro leaflet explants of roses produced adventitious buds when cultured in th e dark for 1 week on Murashige and Skoog (MS) induction medium containing 6 .8 mu M thidiazuron (TDZ) + 0.49 mu M indole-3-butyric acid (IBA) and subse quently transferred to MS regeneration medium containing 2.2 mu M benzylade nine (BA) + 0.049 mu M IBA in the presence of reduced light, at 15 mu mol m (-2) s(-1) photosynthetically active radiation (PAR). Analysis of radiosens itivity by irradiating leaf explants with increasing doses of X-rays betwee n 25 and 100 Gray (Gy) resulted in a decreasing rate of leaf explants regen erating buds from 47% to 0% respectively. The lethal dose for 50% of the re generating explants (LD50) in all the three genotypes was estimated to be 2 5 Gy at a dose rate 2 Gy/s. For the main experiment, doses of 5 and 15 Gy w ere selected and variations were observed between genotypes. Clone RUI 317 had the highest rate of adventitious bud regeneration, with 83.6% (2.5 buds /explant) at 5 Gy and 64% (1.8 buds/explant) at 15 Gy, compared to 89% (3.4 buds/explant) with the untreated control. Significant differences in the p ercentage of bud regeneration of the three genotypes were only observed at 15 Gy in comparison to the control and the number of buds formed per regene rating explant varied between 1 to 4.