Organogenesis and somatic embryogenesis in Foeniculum vulgare: histological observations of developing embryogenic callus

Abstract

Different NAA plus kinetin or BA combinations were tested on Francia Pernod fennel seedlings for callus induction and plant regeneration. Callogenesis from hypocotyls was obtained in all auxin/cytokinin-containing media. The organogenic response was observed especially in presence of NAA plus kinetin. The highest frequency of shoot regeneration was found when the auxin and kinetin were used at a 1:1 ratio. Moreover, a prolonged culture period increased shoot formation. Somatic embryogenesis was tested on several fennel populations. The results gave evidence of the genotypic importance. Two different protocols were used for somatic embryo induction. Using the first protocol among the different fennel genotypes tested, only Francia Pernod showed embryogenic capacity. In this case, from a primary non-embryogenic callus cultured for 12 months in presence of 2,4-D, an embryogenic secondary callus was produced. When transferred to the medium without 2,4-D (agarized or liquid), this gave embryogenic plants in high frequency. As far as the second embryogenic method is concerned, secondary embryogenic callus developed only in the presence of 2,4-D plus kinetin in Francia Pernod genotype. Thereafter, the replacement of those growth regulators by GA₃ into the medium greatly increased the somatic embryo development, especially in `Francia Pernod', but also in `Aboca erbe' callus, a population with a very poor embryogenic capacity. In Francia Pernod, the primary and secondary (embryogenic) calli showed different morphological and histological responses, either when the secondary callus was induced by 2,4-D alone or by 2,4-D plus kinetin. Ontogenetic processes leading to somatic embryo formation are described in this context.