Dry matter and nutrient response of cacao seedlings grown in solution under varying concentrations of aluminum

Authors: Goenaga, Ricardo; Perez, Delvis; Marrero Soto, Angel

Submitted to: Journal of Agriculture of the University of Puerto Rico
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/6/2025
Publication Date: 7/1/2025
Citation: Goenaga, R.J., Perez, D.O., Marrero Soto, A.R. 2025. Dry matter and nutrient response of cacao seedlings grown in solution under varying concentrations of aluminum. Journal of Agriculture of the University of Puerto Rico. 109(2), 239-257. https://doi.org/10.46429/jaupr.v109i2.23103.
DOI: https://doi.org/10.46429/jaupr.v109i2.23103

Interpretive Summary: The most productive soils of the world are already under cultivation, and those available for agricultural expansion are often strongly acid, possessing toxic levels of soil aluminum (Al). High soil Al could drastically reduce crop yields by causing a reduction in root growth and therefore limiting exploitation of soil by roots for moisture and nutrients. Incorporation of lime to the soil is a common practice to ameliorate acidity but it is not very effective below the plough layer and often, lime is not available to farmers with limited resources. Cacao (Theobroma cacao) is grown in many areas of the world where soils are acidic and high in aluminum (Al). However, little is known about the adaptability of cacao to these soils. A greenhouse study was conducted to determine the effects of various levels of Al on dry matter production, plant growth, and nutrient concentration in shoots and roots of 10 cacao genotypes from various genetic groups cacao and to identify potential sources of Al tolerance that can serve as superior rootstocks to this stress. Increasing the Al concentration in the solution from 0 to 4.5 mM resulted in a decrease in total dry weight of 73% and 61%, respectively for season 1 and season 2. Even a small increase in solution Al concentration from 0 to 1.0 mM resulted in over a 40% decline in total dry weight. The results of this study demonstrated no striking genotypical differences for dry matter production in cacao trees grown under Al stress, even at relatively low Al concentrations.

Technical Abstract: Cacao (Theobroma cacao) is grown in many areas of the world where soils are acidic and high in aluminum (Al). However, little is known about the adaptability of cacao to these soils. A 2-season greenhouse study was conducted to determine the effects of various levels of Al on dry matter production, plant growth, and nutrient concentration in shoots and roots of 10 cacao genotypes from various genetic groups. Increasing the Al concentration in the solution from 0 to 4.5 mM resulted in a decrease in total dry weight of 73% and 61%, respectively for season 1 and season 2. Even a small increase in solution Al concentration from 0 to 1.0 mM resulted in over a 40% decline in total dry weight in both seasons. Three genotypes (EET-400, TARS-34, and TARS-14) had an increase in root dry weight until reaching a soil solution concentration of 2.5 mM Al and then decreased. As percentage of the initial average leaf number, average plant height, and average stem diameter, genotype PA-4 exhibited the greatest increase in values for these traits at the end of the experiment in both seasons suggesting that it adapts well to increases in Al concentration in the rhizosphere and deserves further study. The results of this study demonstrated no striking genotypical differences for dry matter production in cacao trees grown under Al stress.