Improvements in rooting regenerated safflower (Carthamus tinctorius L.) shoots.

A continuing obstacle for regenerating safflower (Carthamus tinctorius L.) plants from cultured explants or callus has been a reliable method for rooting shoots. For shoots directly regenerated from primary explants, 76% of shoots rooted after a 7-d exposure to 10 mg/1 indole-3-butyric acid. Auxin source, concentration or exposure time did not greatly affect root formation or morphology, but strongly affected callus production. Shoots infected with Agrobacterium rhizogenes produced massive numbers of fibrous roots, but shoots did not elongate or survive transfer to soil. Shoot hyperhydricity symptoms were reduced by including 1 g/1 activated charcoal in rooting media. The optimal protocol for inducing root formation consisted of a 7-d exposure to 10 mg/l indole-3-butyric acid in root induction media, followed by incubation in media containing 15 g/l sucrose and 1 g/1 activated charcoal for 21 d.