Variants of Digitalis obscura from irradiated shoot tips

Shoot tips excised from genotype T4 of Digitalis obscura were exposed to gamma rays (20–100 Gy). Radiosensitivity was assessed and LD₅₀ determined was about 60 Gy. The effect of the herbicide amitrole on shoot-tip culture was investigated, efficient bleaching was obtained with 10 mg/l amitrole. Shoot tips mutagenized (20–40 Gy) were cultured on several selective amitrole-containing media, but none of them permitted prolonged survival of the green shoots formed. Ploidy level of the plantlets developed was analysed by flow cytometry 8 and 18 months after culture establishment. Variations detected corresponded to aneuploid changes and increased in parallel with the gamma radiation dose. Plantlets developed from irradiated shoot tips presented a high variability in their cardenolide production (878 to 3291 μg/g d.w.), including variants with similar or even higher productivities than the native T4 plant. (author)