High-frequency in vitro shoot regeneration in Cucumis sativus by inhibition of endogenous auxin

Direct in vitro plantlet regeneration was studied in cucumber (Cucumis sativus), an important vegetable crop. The endogenous auxin concentration was quantified by HPLC in young cotyledon explants, and we observed that higher auxin content promotes callusing and inhibits direct shoot regeneration. Lowering the endogenous auxin concentration by the application of the auxin inhibitor 2,3,5-triiodobenzoic acid (TIBA), as confirmed by HPLC, increased the frequency of shoot regeneration. The auxin content was reduced by increasing the concentration of TIBA in cvs. Pant Kheera 1 and Pusa Uday. Regeneration efficiencies were dependent on explant age and cultivar. The 2-d-old explants gave the highest regeneration efficiencies, with Pusa Uday showing higher regeneration potential than PK-1. Shoot buds/small shoots transferred to Murashige and Skoog (MS) medium supplemented with 1 mu M 6-benzylaminopurine grew vigorously and attained 1- to 2-cm length in 4 wk. These shoots rooted with 100% efficiency on MS basal medium or MS basal medium supplemented with 0.5 mu M indole-3-acetic acid. The hardened plants showed normal growth and flowering under greenhouse conditions.