Differential Aluminum Tolerance in Two Snapbean Varieties

Two snapbean (Phaseolus vulgaris L.) varieties, shown previously to differ in tolerance to acid, Al-toxic Bladen soil, were tested more specifically for Al tolerance in nutrient cultures. The Bladen soil-tolerant ‘Bade’ variety was much more tolerant to Al than Bladen-sensitive ‘Romano.’ For example, with 8 ppm Al added, at initial pH 4.8, top and root yields of Dade were 94 and 107%, respectively, of those with no Al. Corresponding top and root yields of Romano were only 53 and 59%, respectively, of those with no Al. With 8 ppm Al added, the total Ca uptake values for Dade tops and roots were 98 and 131%, respectively, of those with no Al; corresponding values for Romano tops and roots were only 25 and 22%, respectively. Aluminum added at 6 or 8 ppm also reduced Ca concentrations in tops and roots of Romano by 30 to 50%, but had little effect on those of Dade. Differential Al tolerance was not related to differential pH changes in nutrient solutions or to Al concentrations of plant tops or roots. With 8 ppm Al added the P concentrations in Romano tops and roots were 60 and 14% higher, respectively, than those of Dade. Aluminum added at 4 ppm decreased stem exudate production of Romano by 66% but did not affect that of Dade. The same Al treatment reduced concentrations of Ca, Mg, K, and P in Romano exudates by 66, 42, 80, and 76%, respectively, but either decreased or failed to affect those of Dade. Lower concentrations of these elements in stem exudates of Al-injured Romano plants were not associated with immobilization hi roots. The 4-ppm Al treatment decreased Ca concentrations in Romano root cell walls, mitochondria, supernatant, and total roots by 55, 68, 51, and 43%, respectively. The same treatment decreased the Ca concentration hi Dade root cell walls by only 27% and that in total roots by 8%, and actually increased the Ca concentration in mitochondria and supernatant fractions by 21 and 63%, respectively. Reduced Ca uptake appears to be a good indicator of Al sensitivity in the two snapbean varieties studied.