Factors Influencing Agrobacterium -mediated Transformation of Brassica rapa L

Transgenic plants of Brassica rapa L. were produced by inoculating hypocotyl sections with Agrobacterium tumefaciens strain EHA101 carrying a binary vector pIG 121Hm, which contains genes for kanamycin-resistance, β-glucuronidase (GUS) and hygromycin-resistance. A cocultivation medium at pH 5.2 with tobacco feeder cells was effective to enhance infection frequency evaluated by the number of hypocotyl sections with transient GUS expression. Transgenic plants in B. rapa cv. Osome were obtained by inoculating the hypocotyl sections in the bacterial inoculum for 30 min, and cocultivation at 25 °C for 3 days with the highest transformation efficiency (percentage of stable transformants per total sections infected) as high as 5 %. Evidence for the transformation was shown by histochemical GUS assay and Southern blot analysis, and segregation of kanamycin-resistance trait and GUS activity in the selfed progeny. The transformation procedure described here was applied to other recalcitrant cultivars in B. rapa.