Influence of 2,4-D and picloram on embryogenic competence of three cassava (manihot esculenta crantz) accessions

The influence of 2,4-D and picloram on embryogenic competence of three local cassava accessions namely, Nkabom, Wenchi and ADI 001 was studied. Young leaf lobes of cassava cultured on MS medium supplemented with 4 to 20 mg/L 2,4-D or picloram (initiation medium) resulted in 90 to 100% embryogenic calli formation depending on the accession. The transfer of embryogenic calli to an MS medium supplemented with 0.1 mg/L BAP produced primary embryos. The duration and number of primary embryos produced on the maturation medium depended on the auxin as well as the genotype. picloram decreased the number of days to maturation and produced comparatively more embryos at both the primary and cyclic stages than 2,4-D. However, the optimal concentration required for increased embryo production in picloram was higher (16 mg/L) than 2,4-D ( 8 mg/L). Fragmentation of matured primary somatic embryos and reculture on initiation medium led to cyclic embryo production. Cyclic embryogenesis doubled (with 2,4-D) or tripled (with picloram) the number of embryos produced at the primary stage. However, recycling of embryos through three successive cycles resulted in a slight reduction in the number of embryos produced. The presence of lower concentration of ABA (1 mg/L) in the maturation medium enhanced embryo maturation and plantlet regeneration while increased concentration of ABA (2 or 4 mg/L) decreased embryo production and plantlet regeneration indicating inhibition or dormancy effect of the growth regulator on germination of embryos. Desiccation significantly (P ≤ 0.05) improved plantlet regeneration from both 2,4-D and picloram-induced somatic embryos in all the accessions. However, comparatively high somatic embryos derived from picloram germinated into plantlets than 2,4-D.This study has shown that all three accessions, are embryogenically competent and picloram is a superior auxin to 2,4-D in somatic embryo production and successful regeneration of plantlets. This holds great potential for the generation of more calli or somatic embryos for irradiation to produce mutant cassava for both domestic, industrial and biofuel usage (au).