Abstract

                                Artificial doubling of the chromosome number has been found to be a fruitful approach in breeding new types of ornamental plants. Its value in floriculture has been well recognized and attempts have been made to produce strains of sexually and asexually propagated ornamental plants with reasonable success (Emsweller and Ruttle, 1941; Bali and Tandon, 1956; Jain et al., 1962). Tetraploid snapdragons, zinnias and marigolds have been introduced in garden. practice (Elliott, 1958) and are favoured for their large flowers and longer flowering period and other attributes of value in floriculture. Reduced seed fertility in the tetraploids is a drawback to be reckoned with in sexually propagated ornamental annuals, which could be overcome by selection and other breeding techniques. Attempts were made to induce tetraploidy in Zinnia linearis and the observations are presented in this paper. This species is a common garden annual of the plains frequently grown for edging and for beds because of its short, compact stature, small leaves, profuse thin-branches and the mass of little, bright-yellow flowers. Two varieties are recognized viz., the yellow and white-flowered types (Bailey, 1957). Forms of this species with larger flowers would be of greater appeal to the floriculturist.

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