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

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 kineti n. 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 inc reased shoot formation. Somatic embryogenesis was tested on several fennel populations. The results gave evidence of the genotypic importance. Two dif ferent protocols were used for somatic embryo induction. Using the first pr otocol among the different fennel genotypes tested, only Francia Pernod sho wed embryogenic capacity. In this case, from a primary non-embryogenic call us cultured for 12 months in presence of 2,4-D, an embryogenic secondary ca llus was produced. When transferred to the medium without 2,4-D (agarized o r liquid), this gave embryogenic plants in high frequency. As far as the se cond embryogenic method is concerned, secondary embryogenic callus develope d only in the presence of 2,4-D plus kinetin in Francia Pernod genotype. Th ereafter, the replacement of those growth regulators by GA(3) into the medi um greatly increased the somatic embryo development, especially in 'Francia Pernod', but also in 'Aboca erbe' callus, a population with a very poor em bryogenic capacity. In Francia Pernod, the primary and secondary (embryogen ic) 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 kine tin. Ontogenetic processes leading to somatic embryo formation are describe d in this context.