Influence of aluminum stress on shoot and root growth of contrasting genotypes of coleus

Abstract

Two cultivars of Coleus blumei Benth., found previously to differ in stress tolerance to UV‐B radiation, water stress, and air pollutants—stress‐tolerant ‘Marty’ ('M') and stress‐sensitive ‘Buckley Supreme’ ('BS')—were grown in a greenhouse at Beltsville, MD in nutrient solutions containing 0 to 24 mg aluminum (Al) L^‐1 (Experiments I and II) and on an acid Al‐toxic Tatum subsoil (clayey, mixed, thermic, Typic Hapludult) (Experiment III) at six lime levels, from 0 to 6,000 μg calcium carbonate (CaCO₃) g^‐1 (pH 4.47 to 7.30 and percent Al saturations from 60 to 0) to characterize their possible genotypic differences in response to Al toxicity. Significant inhibitory effects of Al stress on shoot growth were generally observed in solution culture at 8 mg Al L^‐1 or higher, while inhibition of root growth in solution culture was generally observed at 16 mg L^‐1 or higher. At 16 and 24 mg Al L^‐1 (Experiment II), the relative dry weights of shoots and roots were reduced to about 60% of the control values in both cultivars. Leaf tissue concentrations of phosphorus (P) and Al were increased and calcium (Ca) was decreased at 24 mg Al L^‐1. Both cultivars of Coleus were extremely tolerant to Al stress, both in nutrient solution and in an acid Al‐toxic Tatum subsoil. Thus, Coleus appears to be a calcifuge type plant, resembling azalea in its behavior. The lack of differential sensitivity to Al is in contrast to the responses of these cultivars to other environmental stresses such as drought, UV‐B radiation, and air pollutants.