Effects of gamma irradiation on Dahlia cv. “Pinki” with particular reference to induction of somatic mutation

Rooted stem cuttings of Dahlia cultivar ‘Pinki’ were irradiated with 0, 250, 500, 1000 and 1500 rads of gamma rays at the dose rate 10OGy per 51.8 Sec in gamma chamber-900, 60Co of Floriculture Laboratory, National Botanical Research Institute, Lucknow. LD50 on survival basis was determined in between 1000 and 1500 rads. Reduction in survival, plant height, leaf number and size, length of peduncle, flower size, floret number and size was observed after irradiation and with increase in exposure of gamma rays. Morphological abnormalities in leaf and plant with abnormal leaves increased with increase in exposure to gamma rays. Leaf abnormalities includes asymmetrical development of leaf lamina, notching of different grades, formation of lobes, reduction in leaf let number, leathery texture, fission and fusion of leaf, narrow leaves, chlorophyll variegated leaves and light and dark green leaves. Per cent leaf abnormalities and abnormal plant increased with increase in exposure to gamma rays. A floral abnormality includes fasciations of bud/flower head and reduced flower size. Observation from light and Scanning electron microscopic reveals alteration in stomatal density, change in wax coating and cuticular striations, withering tendency in epidermal cells after gamma irradiation. Mutation appears in foliage in the form of chlorophyll variegation and in the flower head in the form of white sectors in ray florets in VIMl generation after irradiation. On the basis of our observation we recommend 500 and 1000 rads dose of gamma rays for induction of somatic mutation in Dahlia Cultivar ‘Pinki’.