COLCHICINE-INDUCED POLYPLOIDY IN CITRUS EMBRYOGENIC CULTURES, SOMATIC EMBRYOS, AND REGENERATED PLANTLETS

Two morphologically distinct Citrus sinensis (L.) Osbeck embryogenic cultures were grown for 4 or 12 weeks on Murashige and Tucker (MT) medium amended with 0.01% or 0.10% colchicine. Ploidy level frequencies were determined in treated cultures and untreated controls, as well as somatic embryos and regenerated plantlets, by chromosome counts. Mortality was widespread after treatment. The frequency of polyploid cells and the number of ploidy classes was increased by colchicine treatment; the frequency of non-diploid cells in untreated cultures was less than 10%. One line partially reverted back to diploidy, but the other line remained cytogenetically unstable; however, colchicine-induced cytogenetic variation was attenuated through the regeneration process. Although 2x, 3x, 4x, 6x, and 8x cells and somatic embryos were observed, only diploid and tetraploid plantlets were regenerated from treated cultures. Untreated cultures yielded only diploid regenerants.