Somatic embryogenesis of lettuce from mature tissues

The regeneration of somatic embryos (SEs) in tissue cultures derived from mature tissues of lettuce (Latuca sativa L.) is reported. We recently described the regeneration of somatic embryos on a wide range of genotypes, ploidy and tissues of potato (Solanum tuberosum L.) using a two-step protocol in vitro. Using the same protocols, SEs have been regenerated on seven cultivars (cvs.) of lettuce: Butter Crunch, Grand Rapids, Olga, Pluto, Queen Crown, Red sails and Summertime. Seeds from head-, leaf- and romaine-type lettuce plants were germinated, grown in a greenhouse, and axillary shoots from mature plants excised, disinfested and cultured in vitro. Once the shoots had grown into plantlets, the tissues were cultured on a medium lacking growth regulators. Leaf, stem and petiole tissue was excised and used to regenerate SEs. All cultures were grown at 19degreesC under cool-white fluorescent lamps with an irradiance of 100 mumol(.)m(-2) s(-1) and a photoperiod of 16 h. Somatic embryos were also regenerated from seedling tissues of five lettuce cvs. Lettuce SEs germinated without difficulty and acclimatized to greenhouse conditions. Explants (leaf, stem-internode and petiole) from seedlings of all lettuce cvs. regenerated, although stem-internode sections were generally more productive. Regeneration from mature tissues of lettuce was most efficient using leaf and petiole explants.