MICROPROPAGATION OF THEOBROMA CACAO, A RECALCITRANT SPECIES, WITH HIGH CO2

Abstract

Cacao (Theobroma cacao) has long been considered a recalcitrant species in regard to microproagation. Although axillary shoots from cotyledonary nodes will proliferate and grow in vitro provided either cotyledons or roots are attached, excised shoots fail to grow in spite of conventional medium and hormonal modifications. Charcoal supplemented medium and rapid medium change are only marginally effective in inducing shoot elongation. The recalcitrance of cacao appear to be due to the presence of gums which are produced from stem tissues in response to wounding. However, growth of axillary cotyledonary shoots as well as mature shoots was obtained under conditions of high CO 2 (20,000 ppm) and high light (quantum flux of 200 μmol m -2 s -1 ) with or without sugar. Under these conditions leaves develop and shoots elongate which can be subdivided and subcultured. Shoots root under these conditions in vitro. We hypothesize that growth of cacao shoots in response to high CO 2 is due to translocation of metabolizes from photosynthesizing leaves and stems.