Effect of Gamma Irradiation on African Marigold ( Tagetes erecta L.) Cv. Pusa Narangi Gainda

Seeds of African marigold cv. 'Pusa Narangi Gainda' were irradiated with 0, 100, 200, 300 and 400 Grays of gamma rays to induce mutation. Seeds were sown just after irradiation and 30-day old seedlings were transplanted into beds. Reduction in survival percentage, plant height, number of branches, leaf number, leaf size, plant-spread, stem diameter, increased foliage and floral abnormalities were observed upon irradiation and with increase in dose of gamma rays. LD50 was determined on survival basis. Leaf abnormality manifested itself as leathery texture of leaf, enhanced and irregular leaf thickness, asymmetric development of pinnate leaflets, reduction in pinnae number, chlorophyll variegation, pale and deep green leaves, narrow leaves and small leaves. Percentage of abnormal leaves and plants increased with increase in dose of gamma rays. Fasciation of stem was a common abnormality observed in all the treatments. Days to bud initiation, earliness in colour-appearance and days to full bloom were all significantly delayed upon exposure to gamma rays. Flower-head size, height and weight were highest at the lowest dose. Number of ray florets and size (length and width) decreased with increasing radiation dose. Floral abnormalities and % of plants with abnormal flower-heads increased with increasing dose of gamma irradiation. Floral abnormality included fasciation of flower-head and asymmetric development of ray florets. Stimulating effect of gamma irradiation was observed at 100 Grays where almost all the characters studied showed positive correlation, including growth and yield attributes. It is concluded that exposure to 100 Grays of gamma rays in African marigold cv. Pusa Narangi Gainda results in higher yield and marketable bloom.