Impact of selected antimitotic substances on doubled haploid and polyploid regeneration in microspore cultures of swede (Brassica napus ssp. napobrassica (L.) Hanelt)

Several antimitotic agents were tested in three embryogenic doubled haploid (DH) lines of swede (Brassica napus ssp. napobrassica). No effect on embryogenesis was observed at the given concentrations of colchicine (5 mu mol/L or 50 mg/L) and treatment time of 24 hours. Flow cytometric analysis of microspore embryos revealed a significant increase in the percentage of DH compared to the control for all substances: ethalfluralin, 62.2%; trifluralin, 58.3%; colchicine, 56.1%; amiprophos-methyl, 54.4%; pronamide, 35.0%; control, 13.3%. The occurrence of pure tetraploids was low (0-5%), mixoploids especially n+2n were high in all treatments, including the control (29.4-71.1%). Their presence can be explained as a consequence of spontaneous diploidisation and/or endoreduplication during embryo genesis or embryo germination.