Uptake and partitioning of cadmium by cultivars of peanut (Arachis hypogaea L.)

Cadmium has been found to accumulate in peanut ( Arachis hypogaea) kernels to levels exceeding the current maximum permitted concentration in Australi a of 0.1 mg kg(-1). Little is known of the mechanisms of Cd uptake into ker nels by cultivars of peanut, so the aims of the experiments reported here w ere to determine if Cd is absorbed directly through the pod wall or via the main root system, and if differences exist between cultivars in this respe ct. Split-pot soil and sand/nutrient solution experiments were performed wi th two cultivars of peanut (cv. NC7 and Streeton) known to accumulate Cd to different levels in the kernel. The growth medium was separated into pod a nd root zones with Cd concentrations in each zone varied. In confirmation o f previous field trial results, cv. NC7 had higher concentrations of Cd in kernels, given the same Cd levels in the external medium (solution or soil) . Despite total Cd uptake by cv. NC7 being similar to cv. Streeton, cv. NC7 appeared to retain more Cd in the roots and translocate less Cd to shoots. Results from both soil and sand/solution culture indicated that the domina nt path of Cd uptake by peanut was via the main root system, with direct po d uptake contributing less than 5% of the total Cd in the kernel. There was little difference between cultivars in this characteristic. This indicates that unlike Ca nutrition of peanuts, agronomic techniques to manage Cd upt ake will require modification of soil to the full depth of root exploration , rather than just the surface strata where pods develop. Cadmium concentra tions in testa were up to an order of magnitude higher than in the kernel, indicating that blanching of kernels would be effective in reducing Cd in t he marketed product.