ALUMINUM EFFECTS ON GROWTH, PHOTOSYNTHESIS, AND MINERAL NUTRITION OF CACAO GENOTYPES

Abstract A solution culture experiment was conducted in a greenhouse with two cacao genotypes (Catongo and Theobahia). Plants were subjected to seven aluminum (Al) concentrations and Al effects on growth, photosynthesis, and mineral content were assessed. Inter-genotypic differences for Fo, Fm and Fv fluorescences, as well as for Fv/Fm, were observed with increasing Al concentrations. There was a decreasing of Fo, Fm, Fv and Fv/Fm for the Catongo. Increasing Al concentration decreased photosynthetic rate, stomatal conductance and leaf transpiration rate, however, inter-genotypic differences in these parameters were not observed. The Al-treatments decreased content of nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), and magnesium (Mg) in different plant parts, with the exception of K content in stems of Theobahia and in leaves of both genotypes. Theobahia showed higher tolerance to Al phytotoxicity, manifested mainly in the higher levels of Al in the growth medium. Inter-genotypic differences were observed in the growth and mineral nutrition. Keywords: chlorophyll fluorescencedry biomassleaf gas exchangemineral nutrientstoxic aluminum ACKNOWLEDGMENTS The corresponding and senior authors gratefully acknowledges the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), Brazil, for the award of a fellowship of scientific productivity. We thank Dr. C. D. Foy for excellent peer review of this paper.