RESUMO
Some species of Brachiaria, generally tetraploid apomictic varieties, have become important forage grasses in the tropics. Breeding of Brachiaria depends on compatibility with the available apomitic tretraploid cultivars. This paper describes a procedure for chromosome duplication of two Bracharia brizantha diploid sexual accessions, using colchicine treatment of basal segments of in-vitro-grown plants. Explants were cultured on a medium containing 1 mg/l naphthaleneacetic acid, 3 mg/l kinetin and 0.01% colchicine for 48 h and transferred to the same medium without colchicine until shoot regeneration occurred. Regenerated plants were screened by flow cytometry, and chromosome number duplication was confirmed by cytological analysis of root tips.