Induction of powdery mildew resistance in gerbera (Gerbera jamesonii) through gamma irradiation.

In this study, the effect of gamma irradiation in inducing resistance/tolerance towards powdery mildew disease was investigated in Gerbera jamesonii cv. 'Harley'. In vitro shoot cultures were established through capitulum explants on Murashige and Skoog medium supplemented with 22.2 µM 6-benzyladenine (BA) and 2.53 µM indole acetic acid (IAA), followed by gamma irradiation of regenerated shoots (3-5 cm). Activity of four antioxidant enzymes i.e. superoxide dismutase, ascorbate peroxidase, catalase and glutathione reductase increased significantly as compared to the control and reached to highest level at the most stringent doses of mutagen. Ninety randomly selected irradiated plants (6 months old) and 100 control plants were inoculated with fungal conidial suspension, to screen for tolerance/resistance against powdery mildew. The severity of the disease was recorded on 0-4 scale with '0' indicating highly resistant; '1' indicating resistant; '2' indicating medium resistance; '3' indicating susceptible and '4' indicating highly susceptible. Three plants (3.33%) irradiated with 5 Gy were found to be tolerant to powdery mildew as these plants showed slight and delayed development of fungal colonies on the leaves. The random amplified polymorphic DNA characterization showed that the irradiated plants had DNA patterns that were different from the control and mother plants.