SHOOT REGENERATION IN-VITRO FROM DIVERSE GENOTYPES OF SWEET-POTATO AND MULTIPLE SHOOT PRODUCTION PER EXPLANT

Studies were conducted to improve adventitious shoot regeneration in s weetpotato [Ipomoea batatas (L.) Lam.], specifically to extend the pro tocol to many genotypes and to elicit production of multiple shoots pe r explant. The use of a two-stage procedure where excised petioles wer e incubated on Murashige and Skoog (MS) (1962) medium with 2,4-D (0.2 mg . liter(-1) for 3 days and transferred to a second medium containin g MS salts with thidiazuron and 2iP (0.05 mg . liter(-1) each) resulte d in shoot regeneration from eight of 13 genotypes tested, including e lite sweetpotato cultivars such as 'Jewel' and 'Rojoblanco'. PI318846- 3 was the most regenerable genotype, with up to 77 % of explants produ cing one to three shoots per explant. The orientation of the petiole o n the nutrient medium was critical; those placed vertically inverted d eveloped multiple shoots. Wounding explants through epidermal peeling with normal horizontal orientation of the explants during incubation a lso resulted in multiple shoot production (about three shoots per expl ant). Interference with auxin transport due to explant inversion or wo unding may have stimulated increased shoot induction. Chemical names u sed: 2,4 dichlorophenoxyacetic acid (2,4-D); N-phenyl-N'-1,2,3-thiadia zol-5-ylurea (thidiazuron); N-6-(2-isopentenyl) adenine (2iP).