Picolinic acid-induced direct somatic embryogenesis in sweet potato

Somatic embryos are being considered as an alternative material for in vitro germplasm conservation of sweet potato [(Ipomoea batatas (L.) Lam.)]. Picolinic acid was tested for somatic embryo production in sweet potato apical meristem tip cultures. Low level (0.2 mgl^-1) of picolinic acid combined with kinetin or 6-benzylamino purine (6-BAP) (1.0 and 2.0 mgl^-1) suppressed shoot growth and induced callus proliferation. Increased amount of picolinic acid (2 and 3 mgl^-1) in combination with kinetin (0.25 and 1.0 mgl^-1) induced direct somatic embryogenesis from apical meristem tips of variety Regal but not in Jewel. The primary embryos matured and germinated bipolarly yielding whole plantlets and unipolarly producing embryogenic hyperhydrated-fasciated shoots. The hyperhydrated-fasciated shoots, when cultured in picolinic and kinetin-enriched medium, produced secondary embryos. The secondary embryos also germinated bipolarly and unipolarly, resulting in subsequent cycles of embryogenesis. This recurrent embryogenesis ensures maintenance and proliferation of embryogenic tissues. Somatic embryos were also formed in mannitol-induced hyperhydrated shoots in response to picolinic acid and kinetin or 6-BAP treatment. Embryogenesis did not occur in non-hyperhydrated leaf, petiole, and internode sections.