In order to develop an efficient procedure for chromosome doubling of lavandin, leaf-derived calli were treated with colchicine. Relatively high adventitious shoot formation rates, from 71.8 to 79.3%, were obtained in the medium with 0.05, 0.1 and 0.5% of colchicine, although almost all shoots showed hyperhydricity. However, root formation rates were seriously decreased. Conclusively, 2, 16 and 7 chromosome-doubled plants were obtained from calli treated with 0.05, 0.1 and 0.5% of colchicine,

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... ere the regeneration rates were 0.6, 4.3 and 2.0%, respectively. The leaf lengths of chromosome-doubled plants varied widely, and the stomatal size was significantly larger than that of the original. However, both the floral stalks and spikes of chromosome-doubled plants showed dwarfism. Additionally, the essential oil contents in the floral spikes of chromosomedoubled plants significantly decreased. When the crossability is recognized between chromosome-doubled plants and true lavender, these amphidiploids might be interesting materials for improving horticultural traits of lavender.