Evaluation of the potential for somatic embryogenesis in sugar beet (Beta vulgaris L.) breeding lines and improvement of regeneration efficiency

A wide range of genotypes suitable for a plant regeneration system is needed when utilizing genetic transformation techniques to develop new crop cultivars. We examined the regeneration efficiencies for somatic embryogenesis in 61 genetically diverse sugar beet (Beta vulgaris L.) breeding lines developed in Japan using a previously reported procedure. Frequencies of embryogenic callus formation from seedling leaf and petiole explants ranged from 0 to 89% and those of somatic embryo formation from the calli ranged from 0 to 99%. There was no clear correlation between the two frequencies, suggesting that different genetic backgrounds are involved in the two formation mechanisms. To evaluate each breeding line's capability for somatic embryogenesis, we proposed a somatic embryogenesis capability index based on four parameters. Based on the values of this index, only 21 breeding lines were suitable materials for regeneration via somatic embryogenesis. These breeding lines include four lines with moderate or better resistance to three major sugar beet diseases in Japan and one line with strong resistance to these diseases, and these lines will be useful materials with superior characteristics for developing transgenic breeding lines. To increase the regeneration effciencies in the other 40 breeding lines, we examined other types of explants from seedlings and the effects of various plant growth regulators. We found that cotyledon explants generally showed improved callus formation and that using thidiazuron instead of N-6-benzylaminopurine improved somatic embryo formation in some lines.