Screening soybean for aluminium tolerance and adaptation to acid soils

Abstract

Inhibition of root elongation was the most sensitive response of soybean plants to Al in solution culture. Primary-root elongation was confined to the apical 10-mm root tip. Initial response of root elongation to Al seemed to be due to inhibition of cell elongation rather than cell division. Negative correlations existed between Al concentrations of root tips and genotypic root length at low and high Al supply. Using the product of the primary-root length and the longest secondary-root length after 4 days of Al treatment (74 μmol L^-1) relative to the control without Al as parameter, 938 soybean genotypes from the world soybean collection were screened for Al tolerance. Large genetic variability could be found. Elsewhere reported differences in Al tolerance of selected soybean genotypes could be confirmed. However, no relationship existed between genotypic Al tolerance in solution culture and adaptation to an acid soil in Southeast Nigeria reported by UTA (Annual Report, 1981). Therefore a sand-culture screening procedure was established. Compared to solution culture, a 10 times higher Al concentration was necessary to inhibit root growth to a comparable degree. There was a significant but rather weak correlation (r = 0.43) between the responses to Al of 31 genotypes in solution and sand culture. Genotypic response of root growth to Al in sand compared to solution culture was more closely, but still not significantly, related to growth of the genotypes in acid soil under field conditions in Nigeria. This indicates, that inhibition of root growth by Al was not primarily responsible for growth reduction due to soil acidity under those field conditions.