Effects of brassinolide on microspore embryogenesis and plantlet regeneration in pakchoi (Brassica rapa var. multiceps)

•Microspore culture can be used to obtain homozygous doubled haploids (DHs).•We used in three pakchoi genotypes.•Microspore embryogenesis frequency and plant regeneration rate were assessed.•For this, four brassinolide (BR) concentrations were added into NLN-13 liquid medium.•For genotype ‘XM2’, 0.01 mg L−1 and for ‘XM1’ and ‘XM3’, 0.02 mg L−1 BR was optimum.