Abstract
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.
Highlights
Cacao (Theobroma cacao L.) is cultivated extensively as the source of cocoa butter and cocoa powder for the confectionery industry
Significant K effects were observed on growth traits including stem diameter, root length, chlorophyll b, and the ratio of chlorophyll a/b
Genotype difference was found on all measured carbohydrate and starch metabolites, except maltose and raffinose
Summary
Cacao (Theobroma cacao L.) is cultivated extensively as the source of cocoa butter and cocoa powder for the confectionery industry. Four million tons of dry cacao beans are produced in a dozen or so tropical developing countries, where the livelihood of six million farmers depends on cacao production [1]. Poor soil fertility and lack of appropriate fertilization are considered the main contributors to the reduction of cacao yields [5]. As a perennial crop grown in the tropics, soils under cacao are often infertile and acidic due to long term cultivation with little or no fertilizer inputs, loss of nutrients through erosion and nutrient removal by the harvested crops [6]
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