The effects of genotype, intravarietal donor plants, planting density, inflorescence age, bud position, and bud developmental stage on embryo production in Brassica napus L. were investigated. Embryo yields, frequency of normal embryo production, and direct plantlet regeneration were genotype dependent. Embryo yield ranged from 4 to 196 embryos/anther equivalent, normal cotyledonous embryos varied from 6 to 72% of total embryos produced, and direct plantlet regeneration from embryos occurred from 1 to 47% of embryos subcultured. The G231 line was superior in all three factors Embryo production also was affected by the physiological condition of individual donor plants. Dense plantings reduced plant and bud size, leading to reduced microspore production. In some genotypes embryo production was affected negatively at dense planting densities (3 plants/pot), while in others the rate was unchanged, the plants maintaining high embryogenic potential. The highest frequency of embryogenesis was obtained from cultures of buds sampled at approximately 1 week after first flowering and decreased with the aging of the inflorescence. Buds from 2-week-old inflorescences produced fewer embryos and these were generally small, multilobed structures that never developed further into plants. Buds from the lateral racemes and from the primary raceme appeared to be equally capable of embryo production if selected at the appropriate stage of development. Embryogenic microspores commonly were found in buds with a petal/anther length ratio between 1/4 and 3/4, although the optimum embryo yield was from microspores of buds around the 1/2 ratio. Microspores from later bud stages became oval in culture and did not develop further, while uninucleate microspores remained round, and enlarged prior to division.
Microspore culture preferentially selects unreduced (2n) gametes from an interspecific hybrid of Brassica napus L. × Brassica carinata Braun