Effect of Low Temperature Pretreatment of Buds or Inflorescence on Isolated Microspore Culture in Brassica rapa (syn. B. campestris)

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The effect of low temperature pretreatment of buds or inflorescence on microspore culture for the production of haploids of Brassica rapa (syn. B.campestris) was examined. Incubation of the buds or the inflorescence at 4℃ for 3 or 10 days before the culture of microspores induced efficient microspore embryogenesis. Pretreatment of flower buds was more effective than that of the inflorescence. Prolonged pretreatment up to 20 days promoted embryo induction. Microspores in the buds were examined for developmental stage before and after the pretreatment. Buds with a petal length to anther length ratio of about 0.5-0.7, which had microspores were at the late unicellular stage, were collected and were used. All microspores were at the late unicellular stage before the pretreatment. The percentage of the microspores at the stage of late unicellular decreased during the pretreatment while the percentage of bicellular stage microspores with two unequal size nuclei increased. At the same time, a small but notable number of bicellular stage microspores with equal size nuclei, which is the first step of microspore embryogenesis, was observed after the pretreatment.