Responses of cacao to exposed to hypoxia and excess iron in growth, physiology, and nutritional value

Abstract

The growth, enzyme activity, and nutritional value of Theobroma cacao L. are strongly affected under hypoxic conditions and by the toxicity of iron (Fe). It is a challenge to mitigate the stress caused by excessive levels of Fe under flooding in cocoa trees. This study evaluated the physiological response of two cocoa genotypes to different Fe concentrations and hypoxic conditions. The plants were cultivated under three Fe concentrations (44.5, 133.5, and 400.5 μmol L−1 FeSO4) and two hydroponic cultivation conditions, one with an oxygenated nutrient solution and the other solution without oxygenation (hypoxia). Growth characteristics, enzyme activity, and nutritional balance were evaluated at 116 days after planting. An increased guaiacol peroxidase activity and higher phenolic compound contents of genotype TSH 1188 were observed at the Fe concentration of 400.5 μmol L−1 under hypoxia. The genotype SIAL 70 was also recorded increased with rising Fe concentrations, even without aeration. Regardless of the hypoxic conditions, the calcium content of both genotypes decreased with increasing Fe concentrations in the nutrient solution, while the Zn concentration of genotype TSH 1188 increased, regardless of the hypoxic nutrient solution, and that of genotype SIAL 70 decreased under hypoxic conditions. The genotypes respond differently to Fe excess and hypoxia, indicating distinct tolerance mechanisms for each stress type. In general, the tolerance of genotype TSH 1188 and SIAL 70 to the combination of Fe excess and hypoxia, respectively, was high and moderate, suggesting that the two genotypes have different mechanisms to support these stress conditions.