Tolerance to aluminum toxicity by tropical leguminous plants used as cover crops

The objectives of this work were to compare Al tolerance among 17 species of tropical leguminous plants and to evaluate the most appropriate plant characteristic and Al concentration in nutrient solution for tolerance assessment. In addition, three soybean cultivars were included for comparison purposes. There was a great difference among the 17 plant materials tested, when compared by relative root elongation and critical Al activity to reduce 50% of root net elongation. Based on these parameters and on the comparison of two tropical maize genotypes differing in Al tolerance, the following classification was established: highly tolerant for Mucuna nivea, M. deeringiana, m. aterrima Vigna unguiculata cv. BR 17 and Lablab purpureus cv. Rongai; tolerant for Cajanus cajun cv. IAPAR 43, Canavalia brasiliensis Calopogonium mucunoides, Cajanus cajan cv. Fava larga, and Crotalaria paulina; moderately tolerant for Crotalaria ochroleuca, Canavalia ensiformis, Crotalaria spectabilis, and C. mucronata; and sensitive for Neonotonia wightii, Crotalaria breviflora and C. juncea cv.IAC-KRJ. The three soybeans cultivars were classified as moderately tolerant (Biloxi) and tolerant (IAC 13 and IAC 9).