Investigation Of The Effects Of Mycorrhizal Fungi On Cadmium Accumulation In Cacao

Currently, increasing emphasis is being placed on the contamination of cacao beans by heavy metals, particularly cadmium (Cd). Since the primary source of Cd contamination in cacao has been attributed to metal-contaminated soils, it is becoming crucial to develop strategies to minimize its uptake. Recent studies have shown that mycorrhiza could contribute to the immobilization of Cd in soils, thereby decreasing Cd toxicity to plants. A preliminary pot trial study was designed to determine whether mycorrhizal fungi in the form of bio-fertilizers could be used as a method of soil remediation, to inhibit Cd uptake by cacao plants. Roots of cuttings of a single variety and age of cacao were grown with and without a commercial bio-fertilizer, in a Cdspiked, sterilized soil in pots, in randomized blocks in a greenhouse. The experiment was conducted over a period of four months, with replicates of plants being sacrificed and analyzed monthly, to determine the Cd contents of leaf and stem samples. Microscopic examinations were also done to detect mycorrhizal infection of roots of bio-fertilizer treated and control plants. Paired data analysis demonstrated that cacao plants treated with the mycorrhizal bio-fertilizer accumulated significantly higher (p<0.05) levels of Cd in both leaves and stems than nonmycorrhizal- treated plants for the period of the study. The higher Cd concentrations found for the mycorrhizal treatment may have resulted from an increase of Cd absorption into the plants by soil mycelia, known to spread several centimeters around the plant roots. This investigation, while preliminary, indicates that the variety of cacao plant used with the commercial mycorrhiza used accumulates significantly higher levels of Cd in their leaves and stems than non-mycorrhizal plants.