Tolerance and uptake of cadmium, arsenic and lead by Fusarium pathogens of cereals

The effect of the heavy metals arsenic (As3), cadmium (Cd2) and lead (Pb2+) over the range 10–75 ppm on growth of six Fusarium pathogens of cereals (F. avenaceum, F. culmorum, F. graminearum, F. moniliforme, F. poae and F. proliferatum) was investigated on a 1% malt extract agar. Overall, growth of species was inhibited by increasing concentrations of Cd, and stimulated by low concentrations of As, and by 10 ppm Pb. The most tolerant species of the three metals were F. avenaceum, F. culmorum and F. moniliforme. Temporal studies of the effect of interactions between metal concentration (25 ppm), pH and water availability were carried out in a 1% malt broth over 20 day periods. The optimum pHs for metal uptake by F. avenaceum were 5.6 for As and Pb, and 7.0 for Cd; for F. culmorum 4.0, 7.0 and 5.6 and for F. moniliforme 5.6, 7.0 and 4.0, respectively. As water activity (aw) was decreased from 0.998 to 0.95, the ability of the Fusarium spp. to take up the metals was markedly reduced. Studies with fresh and dried mycelial biomass demonstrated that 60–70% of the three metals were actively taken up by the three Fusarium spp., with the remainder being passively bound to the mycelium.