Somatic embryogenesis in sweetpotato is highly genotype dependent. Unfortunately, many desirable agronomic varieties do not produce embryos capable of germination when published protocols are followed. Using one responsive and three recalcitrant cultivars, we examined the effect on embryogenesis of auxin, nitrogen, and carbon; explant source; and desiccation. All cultivars formed proembryonic masses on medium supplemented with either 2,4-D or picloram; picloram favored the growth of nonembryogenic callus. Twenty mm each of ammonium and nitrate promoted the best proembryo formation in all cultivars. Ammonium was essential for embryogenesis; replacing ammonium with proline, glutamine, asparagine, glycine, or casein hydrolysate resulted in poor or no proembryo formation. More proembryos formed on medium supplemented with sucrose than with glucose, fructose, or maltose. Leaf discs from the first fully expanded leaf produced more embryos than younger leaves for all cultivars; discs taken from the lamina produced more embryos than discs including portions of the midrib. Proembryos matured and germinated only after at least 3 weeks on medium containing 5% w/v polyethylene glycol 8000, greater than 3.3 mmmyo-inositol, and 1 or 10 μm abscisic acid. More whole plants were obtained from the responsive cultivar Jewel than from the recalcitrant genotypes.
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