The effect of pretreating seedlings with TDZ on direct shoot regeneration from petiole explants of sugar beet (Beta vulgaris L.)

A 100% seed sterility and 75.6% seed germination rate were achieved when seeds of three sugar beet (Beta vulgaris L.) breeding lines were surface sterilized with a combination of 0.5% Domestos and 5% PPM™. The procedures we describe here are more successful than the previously published procedures as a high rate of sterility was achieved without reducing the germinability of sugar beet seeds. As an in planta treatment with TDZ (thidiazuron), the sterilized seeds were germinated on MS basal medium containing 1, 3 or 5 mh/L TDZ for five weeks and then petiole explants were excised from the seedlings and cultured on two different regeneration media; RGL medium containing 0.5 mg/L BAP and 0.1 mg/L NAA, and RGH medium containing 1.0 mg/L BAP and 0.5 mg/L NAA. Petiole explants taken from seedlings pretreated with 1 mg/L TDZ produced significantly more shoots (1.67 shoots per explant) than those taken from seedlings pretreated with 3 or 5 mg/L TDZ (1.1 6 and 0.92 shoots per explant, respectively). The RGL medium containing lower BAP and NAA was significantly more effective in direct shoot production than the RGH medium containing higher BAP and NAA, 1.54 shoots per explant compared to 0.96, respectively. Such an increase in regeneration capacity of the explants due to the TDZ pretreatment is clearly significant for sugar beet, which is regarded as a recalcitrant species. 42.6% of the regenerated shoots developed roots on medium containing 3 mg/L NAA whereas only 19.3% of the shoots rooted on medium containing 1 mg/L NAA. Genotypic variation was significandy evident for both shoot regeneration and rooting.