Improved plant regeneration from maize callus cultures using 6-benzylaminopurine

A new protocol for regenerating plants from cultured type I callus of the maize (Zea mays L.) inbred Pa91 includes growing the callus on medium containing 3.5 mg/l (15.5 μM) of the cytokinin 6-benzylaminopurine (6BA) for 3 to 6 d and then moving the callus to medium containing no growth regulators (H medium) for an additional 15 to 21 d, where the plants actually develop. The number of plants regenerated from the 6BA treated callus was 113% to 148% greater than the number of plants produced from callus placed directly on H medium. This increased plant regeneration induced by 6BA seemed to maximize the number of plants regenerated from a gram of callus and was slightly affected by callus age or prior treatment of callus with AgNO3. Exposure to 6BA for 9 d greatly reduced shoot and root development, and longer exposures totally prevented root formation. This inhibition of root formation could be reversed only slightly by naphthaleneacetic acid. The data indicate that high concentrations of 6BA are effective for increasing plant regeneration from maize callus cultures when short exposure times are used. This procedure has also been effective for regenerating many plants from the inbreds H99 and Mo17.