Physiological traits and metabolites of cacao seedlings influenced by potassium in growth medium

Authors: LI, YAN-MEI - Chongqing University; Elson, Marshall; Zhang, Dapeng; Sicher Jr, Richard; HANG, LI - Chongqing University; Meinhardt, Lyndel; Baligar, Virupax

Submitted to: American Journal of Plant Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/15/2013
Publication Date: 5/1/2013
Publication URL: https://handle.nal.usda.gov/10113/59019
Citation: Li, Y., Elson, M.K., Zhang, D., Sicher, Jr., R.C., Hang, L., Meinhardt, L.W., Baligar, V.C. 2013. Physiological traits and metabolites of cacao seedlings influenced by potassium in growth medium. American Journal of Plant Sciences. 4:1074-1080.

Interpretive Summary: Cacao has significant economic importance to many resource poor farmers in the tropics. Yields of cacao are very low due to low soil fertility, in particular inadequate supplies of soil potassium (K) that greatly affects the yields. Research was undertaken to evaluate the effects of deficit to excess levels of soil K on the growth and metabolites of several cacao genotypes. The research findings of this paper reveal a critical role of potassium in the growth and development of cacao. Significant improvements were observed for specific physiological traits and in the starch and glucose levels of the cacao genotypes that were tested. These results improved our understanding of K/plant interactions in cacao seedlings, which is useful for crop management, plant breeding and fertilizer recommendations. The methods adapted for this study are useful for the identification of potassium efficient cacao genotypes. The knowledge of how K use in cacao will help cacao farmers develop better crop and fertilizer management practices to improve cacao sustainability and improve yields. Furthermore, this knowledge will help plant breeders and scientists identify and develop potassium efficient cacao genotypes that will improve cacao sustainability and adaptation to potassium poor soils.

Technical 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.