Abstract: In this study, the tube plantlets of broccoliwere cultured on Murashige and Skoog fluid medium supplemented 6-BA and NAA in combinationswith different concentrations of colchicine and treatment time to induce tetraploid. The results showed that the treatmentwith 200 mg· L - 1 colchicines inMS + 011 mg·L ^{- 1} NAA + 6.0 mg·L ^{- 1} 6-BA for 48 hours yielded doubled chromosomes at highest rates, the number of shoots per exp lant was 2.1, the variation efficiency was 83.33% , and the variational rate of tetrap loid was 79.17 %. Compared with the dip loid, the tetrap loid plants possessed gigantism in leaves, floral, stomata of plantlets. The flow cytometry was used to identify the ploidy of induced plants. The result suggested that the relative DNA content of controlwas 200 and the number of chromosome was 2n = 2x = 18, and tetrap loid relative DNA contentwas 400 and the number of chromosome was 2n = 4x = 36. The identification of the chromosome analysis indicated the regeneration plantletswere tetraploid.

Key words: Brassica oleracea L. var. italica Planch., in vitro culture, colchicines, tetraploid