Growth and nutritional responses of juvenile wild and domesticated cacao genotypes to soil acidity

Authors: AREVALO-HERNANDEZ, CESAR - Tropical Crop Institute (ICT); AREVALO-ARDINI, ENRIQUE - Tropical Crop Institute (ICT); FARFANA, ABEL - Tropical Crop Institute (ICT); AMARINGO-GOMEZ, MARTINA - Tropical Crop Institute (ICT); DAYMOND, ANDREW - University Of Reading; Zhang, Dapeng; BALIGAR, VIRUPAX - Retired ARS Employee

Submitted to: Agronomy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/12/2022
Publication Date: 9/12/2022
Citation: Arevalo-Hernandez, C., Arevalo-Ardini, E., Farfana, A., Amaringo-Gomez, M., Daymond, A., Zhang, D., Baligar, V. 2022. Growth and nutritional responses of juvenile wild and domesticated cacao genotypes to soil acidity. Agronomy. 12(12):3124. https://doi.org/10.3390/agronomy12123124.
DOI: https://doi.org/10.3390/agronomy12123124

Interpretive Summary: Cacao (Theobroma cacao L.) is an important cash crop of the tropical world. It provides raw materials for the manufacture of chocolate. Modern cacao cultivation requires high input of fertilizer to obtain maximum yield. Nevertheless, soils where this crop is grown are in general acid and low in fertility. Cacao germplasm with tolerance to soil acidity are desirable for mitigating this abiotic stress. Growing cacao clones with tolerance to soil acidity offer an alternative solution to mitigate the stress of soil acidity. The present study evaluated 60 cacao accessions for early growth, nutrient concentration, and tolerance to soil acidity in a greenhouse experiment. Cacao seedlings were grown for six months in an acid soil with and without liming. Growth parameters and the total concentration of macro and micro-nutrients were measured in shoots after harvest. Significant difference of acidity tolerance was observed among the 60 cacao clones. The result led to the selection of 10 top ranking clones that showed high level of acidity-tolerance and nutrient use efficiency. These selected clones can be used as rootstock or as parental lines for breeding new cacao varieties. Use of such improved varieties in cacao farming systems appears to be one of the important management strategies in improving cacao yield potentials on acidic and low fertility environment. This information will be used by cacao agronomists, breeders and producers to improve cocoa productivity, especially in areas where small farmers may not have access to soil amendments such as lime to correct soil acidity constraints.

Technical Abstract: Cacao (Theobroma cacao L.) is an important cash crop of the tropical world. It provides raw materials for the manufacture of chocolate. Modern cacao cultivation requires high input of fertilizer to obtain maximum yield. Nevertheless, soils where this crop is grown are in general acid and low in fertility. Cacao germplasm with tolerance to soil acidity are desirable for mitigating this abiotic stress. The objective of this study was to evaluate cacao germplasm for early growth, nutrient concentration, and tolerance to soil acidity. A greenhouse experiment was conducted to evaluate 60 cacao genotypes with diverse geographic origin. Cacao seedlings were grown for six months in an acid soil with and without liming. Growth parameters and the total concentration of N, P, K, Ca, Mg, Fe, Cu, Mn, and Zn were measured in shoots after harvest. The results showed that the number of leaves and the root area can be used as predictors for acidity tolerance in cacao. Under acid soil conditions, N, Ca, Mg and K uptake may have a special role in tolerance to soil acidity. Moreover, the evaluation results revealed large difference among cacao genotypes in terms of their responses to acid soil stress, which lead to the selection of 10 top ranking genotypes. These acidity-tolerant genotypes can be used as rootstock or as parental clones for breeding new varieties, which can be deployed in areas were small farmers may not have access to soil amendments such as lime to correct soil acidity constraints