Aluminum tolerance in sorghum and bean ‐ methods and results

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Abstract
Average pH of Brazilian soils is circa 5.5 and in case of the “cerrado” (around 2.0 million square kilometers) is even lower. Low Ca, Mg and K in the exchange complex is accompanied by high Al saturation. Lime use has not kept up with the increase in fertilizer consumption which is a contributing factor for further decrease in pH. Hence the interest of screening and breeding varieties of food crops with some degrees of tolerance to Al toxicity. This paper summarizes results obtained in experiments designed to differentiate among 30 cultivars each of grain sorghum and beans those less sensitive to high levels of Al in the medium, as well as to establish rapid methods for screening, and to determine relationship between aluminum effect and mineral nutrition. Care was taken to separate Al from H ion effects. Preliminary trials showed that dry matter production by seedlings grown for short periods gave better indication of Al tolerance than other parameters. Very close correlations were found to exist between radiophosphate uptake either by excised roots or intact plants and Al tolerance. Al toxicity was associated to a large degree to reduction in uptake of Ca, K, and particularly Mg in short term experiments. Al‐tolerant sorghum hybrids however showed an increasing K uptake when the concentration of aluminum in the substrate was raised. Although differences do exist among cultivars, it is not thought that this characteristic fully obviates the need for use of lime.