Strawberry sepal: Another explant for thidiazuron-induced adventitious shoot regeneration

An efficient system to regenerate shoots on excised sepals (calyx) of greenhouse-grown 'Bounty' strawberry (Fragaria x ananassa Duch.) was developed in vitro. Sepal cultures produced multiple buds and shoots without an intermediary callus phase on 2-4 mu M 1-phenyl-3-(1,2,3-thiadiazol-5-yl) urea (thidiazuron, TDZ)-containing shoot induction medium within 4-5 wk of culture initiation. Young expanding sepals with the adaxial side touching the culture medium and maintained for 14 d in darkness produced the best results. In a second experiment, sepals proved more effective than the leaf discs and petiole segments for regenerating shoots. A third experiment compared the effects of six concentrations of two cytokinins (TDZ at 0, 0.5, 2, and 4 mu M and zeatin at 2 and 4 mu M) for elongation of sepal-derived adventitious shoots. The media containing TDZ generally promoted more callus formation and suppressed shoot elongation. TDZ-initiated cultures transferred into the medium containing 2-4 mu M zeatin, produced usable shoots after one additional subculture. Shoots were rooted in vitro in the same medium used for shoot regeneration, but without any growth regulators. When transferred to potting medium, 85-90% of in vitro plantlets survived.