Cacao (Theobroma cacao L.) is of
significant economic importance in several tropical countries but its yield
potentials are low mainly because of poor soil fertility especially low levels
of potassium (K). Cacao has a high demand for K to maintain healthy growth and
production. Knowledge of K use in cacao will help the development of suitable
crop management practices and will aid breeding varieties adapted to
environments with a limited soil K supply. Using a plant growth chamber, we
investigated the growth and physiological traits among three cacao varieties at
three levels of growth medium K (52, 156, and 469 mg·plant-1). Significant K effects were observed on growth
traits including stem diameter, root length, chlorophyll b, and the ratio of
chlorophyll a/b. Significant K effect was also found on carbohydrate
metabolites, such as fructose, glucose, myo-inositol, raffinose and starch.
However, no K effect was observed in other growth and physiological indicators,
including biomass of seedling and net photosynthetic rate. There were
significant genotype differences on seedling growth indicators, including stem
diameter, stem height, total biomass, leaf biomass, leaf area, root length,
chlorophyll a + b and carotenoids. Genotype difference was also found on all
measured carbohydrate and starch metabolites, except maltose and raffinose.
Results of this study indicate that although K plays a critical role in cacao
tree growth and productivity, cacao may be less sensitive to K deficiency
during the seedling stage. The present results improved our understanding about
K and plants interaction in cacao seedlings, which is useful for crop
management and germplasm utilization.