Influence of genotype, plant growth temperature and anther incubation temperature on microspore embryo production in Brassica napus ssp. oleifera

Eleven Fx hybrid genotypes of winter rape (Brassica napus ssp. oleifera) were used in a study of induction and growth of microspore-derived embryos. Plants of each genotype were grown in controlled environments at either a constant 15 CC or a constant 20 °C, both with a 16 h photoperiod. Equal numbers of buds, approximately 2-5 mm in length, containing uninucleate microspores were harvested from each genotype and either pretreated (14 d at 4°C) or dissected immediately after harvest. Anthers were cultured on liquid medium based upon that of Murashige and Skoog (1962) and containing 8% sucrose, 0-5 mg dm-3 naphthylacetic acid and 0-05 mg dm-3 benzylaminopurine. Anthers from equal samples of buds were incubated at 35 °C for 0,1, 2 or 3 d before transfer to 30 °C (21 d) and then 25 °C. After a total of 42 d incubation, cultures were scored for the presence of macroscopic embryos (1-2 mm in length) and for the presence of anthers containing aborted embryoids which had not developed further. The results showed first that bud pretreatment completely inhibited induction and secondly that anthers of all genotypes had an absolute requirement for a 35 °C treatment (optimal duration 2 d) in order to induce embryoid formation. In the great majority of genotypes plants grown at 15 °C provided ore productive anthers than plants grown at 20 °C. However, within each treatment there were great differences both in the frequency of anthers showing induced embryoids and of the final yield of embryos. There was evidence that hybrids with a common parent responded similarly under certain treatments. This confirmed the importance of genotypic control for some components of embryo yield