An Efficient Protocol for Agrobacterium -Mediated Transformation and Regeneration of Sugar Beet ( Beta vulgaris L.) based on Blade–Petiole Transition Zone Explants

Sugar beet ( Beta vulgaris L.) is an economically important crop, which contributes significantly to the global sugar supply. The present study was performed to establish and optimize the parameters of Agrobacterium -mediated genetic transformation with the sugar beet blade–petiole transition zone as explants to provide a reliable and efficient genetic transformation method for studies of sugar beet. This study used beet pollination line 32467. In the explants screening test, the differentiation rate of the explant blast–petiole transition zone was 10.8%, which was significantly higher than those of hypocotyl segments (6.7%) and multiple shoot clumps (4.2%). In the medium selection test, the main medium components used in the transformation process were as follows: induced differentiation medium: MS medium, 1.2 mg kinetin, 0.7 mg 1-naphthylacetic acid (pH 5.8); rooting medium: MS medium, 1.2 mg 1-naphthylacetic acid (pH 5.8); infection medium: MS medium, 0.7 mg 1-naphthylacetic acid, 1.2 mg kinetin, 29 mg acetosyringone (pH 6.8); co-cultivation medium: MS medium, 29 mg acetosyringone, 0.7 mg 1-naphthylacetic acid, 1.2 mg kinetin, 388 mg d -galacturonic acid (pH 5.8); delayed selection medium: MS medium, 0.5 mg benzylaminopurine, 0.05 mg 1-naphthaleneacetic acid, 500 mg carboxypenicillin, 100 mg cefotaxime (pH 5.8); and selection medium: MS medium, 0.5 mg benzylaminopurine, 0.05 mg 1-naphthaleneacetic acid, 500 mg carboxypenicillin, 100 mg cefotaxime, 0.013 mg glyphosate (pH 5.8). The results of Agrobacterium infection experiments showed that the optimal Agrobacterium infection concentration was OD 600 = 0.4 with an infection time of 20 minutes.