Total of fifty accessions of Brassica rapa with various morphological characteristics were used for production of double haploid plants though microspore culture in Brassica rapa. Among them, only 30 accessions induced embryos from microspores. The highest efficiency of embryo induction of 1.194 per bud was obtained from IT135449 of turnip type, while 3 accessions of sarson (winter oil) type did not generate embryo. The effect of heat shock periods for embryogenesis was also investigated with 4 accessions (IT135449; Turnip type, IT199710; Chinese cabbage type, IT212886; Pak choi type, IT218043; Summer oil type). The high productions of embryos were observed in IT135449, IT199710 and IT212886 when microspores were pre-cultured to 32˚C for 2 days. In IT218043, high embryogenesis was observed at the 3 days of heat shock treatment. The optimal condition of shoot regeneration for IT199710 was observed in MS medium supplemented with NAA 0.5 mg·L^-1 and BAP 1 mg·L^-1. In contrast, the IT135449 and IT212886 were observed high regeneration frequency in MS medium without plant growth regulators. All the plantlets regenerated from microspore-derived embryos have been successfully transplanted to soil, and bud self-pollinated seeds were produced from doubled haploid plants. This indicated that double-haploid genotype was likely generated naturally during embryogenesis process.

Keywords: Brassica rapa, Microspore, Embryogenesis, Heat shock period, Regeneration