Abstract
In vitro chromosome doubling of nucellar embryos was investigated in Meiwa kumquat (Fortunella crassifolia Swingle). Nucellar embryos were aseptically treated with two antimitotic agents, colchicine and oryzalin at different concentrations and times. After these treatments, nucellar embryos were successively cultured on MT medium containing 500 mg/liter−1 malt extract. Ploidy levels of seedlings were evaluated by both flow cytometry and chromosome counting of root tips. Frequency of tetraploid production depended on the kind of antimitotic agents as well as on the concentration and time of treatment. Among the treatment conditions tested, colchicine gave better results than oryzalin on inducing chromosome doubling. Tetraploid plants were obtained from approximately 50% of the nucellar seedlings treated with colchicine at 0.05% for 48 hours. These tetraploids showed poor growth during the early stage after acclimatization, but grew as vigorously as the diploid plants when grafted onto 3-year-old seedlings of trifoliate orange. These results showed that colchicine treatment combined with embryo culture is particularly efficient to induce chromosome doubling of nucellar embryos in Meiwa kumquat.
