Saturday, 15 July 2006

Can Sorghum Genotypes Avoid Phosphorus Poisoning?.

Rafael G. Camacho Sr.1, Euripedes Malavolta Sr.2, Jose P. Guerrero Sr.1, and Tomas Camacho Jr.1. (1) Romulo Gallegos Univ, Urb. El Castrero, Ciudad Universitaria, CIESA-UNERG, San Juan de los Morros, Venezuela, (2) CENA/USP, Lab. Nutrição Mineral de Plantas, Piracicaba, Brazil

The current study was carried out to determinate if high P concentrations in the nutrient solution interfere with the sorghum genotype ability to absorb phosphorus and grown adequately. Plants were grown in controlled environment conditions through growth stage. In hydroponic cultures with Hoagland's solution, the sorghum was exposed at three [P]s (0, 0.5 and 1mM) for three weeks. Plants were harvested for dry matter determination, uptake 32P by excised roots, and leaf [P]. Root weights decreased with increasing the P levels in the culture solutions, while shoot and total dry matter showed the opposite effect. Except for Criollo-2, leaf [P] was lightly held or reduced by enhancing P from 0.5 to 1.0 mM, being that Himeca-101 showed the strongest drop in the total P concentration (a fall of 1.10 g kg-1). As it might expect, significant negative correlations were found among radiophosphorus uptake by excised roots and: [P] in the nutrient solution, shoot dry matter (with the exception of Himeca-101 genotype) and leaf [P]. All genotypes but Sefloarca-7 reduced the rates of 32P absorption when grown in substrates with P excess; however, Himeca-101 showed highest ability to decrease the P-uptake. These data suggest that sorghum plants can stop or reduce the uptake of P when grown at elevated [P]s, avoiding therefore phosphorus poisoning. However, some genotypes are more responsive than other genotypes.

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