High frequency spontaneous production of doubled haploid plants in microspore cultures of Brassica rapa ssp. chinensis

Brassica rapa (syn. Brassica campestris) ssp. chinensis is an important vegetable crop, but it is relatively recalcitrant to microspore culture. One genotype each of B. rapa ssp. chinensis var. communis and var. utilis were used for microspore culture. Embryo production of 3.8–42.4 embryos/bud was obtained. A high rate of plant regeneration directly from microsporederived embryos without subculture was achieved by an improved protocol involving replacement of culture media and reduction of sucrose concentrations after 48 h of induction, among other modifications. More than 70% of regenerated plants were spontaneous diploids. Some spontaneous tetraploid plants were also obtained from isolated microspores of both genotypes tested. These tetraploids may be directly exploited as new varieties in a Brassica rapa breeding programme.