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Coffee machine
For growers who wish to propagate an elite strain in large numbers, somatic embryogenesis is a possible route. In this technique, callus cultures are established and the formation of non-sexual embryos is induced. However, many such embryos fail at the 'germination' stage or during early 'seedling' growth. The plantlets are often susceptible to water loss and many fail to make the transition from heterotrophic nutrition to an autotrophic existence based on photosynthesis. Afreen and co-workers at Chiba University (pp. 11-19 and 21-29) have extensive experience of working with somatic embryos of coffee (Coffea arabusta). In their two papers they describe the production of plantlets from somatic embryos on a commercial scale. It was first necessary to obtain somatic embryos in which the cotyledons develop functional chloroplasts and start to photosynthesize. The next step was to induce these photoautotrophic embryos to 'germinate' to form plantlets, and finally it was necessary to harden these plantlets to more normal regimes than those of a growth chamber. The authors thus developed a 'bioreactor' in which circulation of CO2-enriched air was provided by forced ventilation. Nutrient solution was provided by partially immersing the root zone of the growth plugs for 15 min every 6 h. This was done mechanically, using an air pump on a time-switch. The plantlets were maintained in the bioreactor for 45 d and then transplanted into a glasshouse; survival was monitored 15 d later. The results were remarkable: 90 % of the embryos developed a root system and 84 % survived the transfer to glasshouse conditions (the authors called this 'plantlet conversion rate'). This rate was approx. 1.6 times better than the next best system and, furthermore, plantlets established by this method also grew faster than those established by other techniques. However, we still wait to find out how the coffee tastes!
Professor J. A. Bryant
University of Exeter, UK
j.a.bryant{at}exeter.ac.uk
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