Scale-up micropropagation of vegetable species: From laboratory to commercial reality

The efficient, commercial-level use of bioreactor systems for the scale-up micropropagation of vegetable species is demonstrated for cucumber (Cucumis sativus L.). Nodal explants were derived from aseptically grown seedlings of the cucumber F-1 hybrid 'Stella' and bearing four leaves. Explants were inoculated on gelled Murashige and Skoog (MS) basal medium supplemented either with no growth regulators or the antigibberellin flurprimidol at 0.5 mg l(-1). Explants were incubated in Magenta(R) boxes under a photosynthetic photon flux density of 150 mumol m(-2)s(-1) at 24degreesC. After one month, nodal clusters were transferred into liquid MS medium with the same composition as above and incubated twice in either: (1) 2.5 1 airlift bioreactors (Osmotek Lifereactors(R)) or (2) 250 ml flasks on an orbital shaker (80 rpm) for 20-30 days. Regenerated plantlets were transferred to soil and acclimatized in the greenhouse. Significantly more plants were regenerated in bioreactors than in Magenta boxes(R) or in flasks. In addition, bioreactor-derived plants had an increased fresh and dry weight, number and length of roots, number of nodes and leaf surface. These traits were associated with patterns of macronutrient and sugar accumulation, as well as ascorbic acid and free antioxidant phenolics concentration. The percentage of plants that were successfully acclimatized increased to 95% after grafting them on squash. The prospects for applying this technique to other cucumber varieties, as well as other commercially important vegetable species, are discussed.