Submitted to: Journal of Plant Nutrition
Publication Type: Peer reviewed journal
Publication Acceptance Date: 9/13/2011
Publication Date: 3/5/2013
Publication URL: http://handle.nal.usda.gov/10113/59035
Citation: Ribeiro, M.A., Almeida, A.F., Mielke, M.S., Gomes, F.P., Pires, M.V., Baligar, V.C. 2013. Aluminum effects on growth, photosynthesis, and mineral nutrition of cacao genotypes. Journal of Plant Nutrition. 36:1161-1179. Interpretive Summary: In tropical soils, Aluminum (Al) is the major mineral component of soil that is highly toxic to crops. In Brazil, cacao is cultivated mainly on soil where Al toxicity and nutrient deficiencies are the main constraints. An experiment was conducted in a greenhouse with several levels of Al to assess Al effects on growth, photosynthesis, and mineral nutrition of two cacao types. Increasing Al concentrations decreased the growth, rate of photosynthesis, and mineral contents. The different varieties showed tolerance to Al, the Theobroma hybrid showed higher tolerance to Al toxicity than var Catongoa. These varietal differences could be useful to breed acid soil tolerant, high yielding cacao cultivars. Such improved cacao cultivars could reduce the cost of production and enhance yield potentials of resource poor cacao farmers in Brazil and in the Americas. This information will be used by cacao researchers and plant breeders.
Technical Abstract: A solution culture experiment was conducted in a greenhouse with two cacao (Theobroma cacao L.) genotypes, resistant (Theobahia hybrid) and susceptible (var. Catongo) to witches’ broom diseases (Moniliophthora perniciosa). Plants were subjected to seven Al concentrations (0, 5, 10, 15, 20, 25 and 30 mg L-1) and, 90 d after the application of Al (DAAT), Al effects on growth, chlorophyll (Chl) fluorescence, leaf gas exchange, and mineral content (P, K, Ca, Mg, Al) were assessed. Inter-genotypic differences for basal (Fo), maximal (Fm) and variable (Fv) fluorescences, as well as for maximum quantum efficiency of the photosystem 2 (Fv/Fm), were observed with increasing Al concentrations in growth medium. There was a decreasing of Fo, Fm, Fv and Fv/Fm for the Catongo with Al increase. Increasing Al concentration, in the growth medium decreased net photosynthetic rate (Pn), stomatal conductance to water vapor (gs) and leaf transpiration rate (E), however, intergenotypic differences in these parameters were not observed. In addition, Al-treatments decreased content of N, P, K, Ca and Mg in different parts of plants, with the exception of K content in stems of Theobahia and in leaves of both genotypes. The Theobahia hybrid showed higher tolerance to Al phytotoxicity than the var. Catongo, manifested mainly in the higher levels of Al in the growth medium. Intergenotypic differences were observed in relationship to growth and mineral nutrition.