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Some species of plant growing on calamine soils hyperaccumulate heavy metals from those soils in their tissues. This study tests the hypothesis that such metal accumulation confers a benefit to the plant by providing defense against fungal pathogens, using the Zn-hyperaccumulator Thlaspi caerulescens (J. & C. Presl.) and the pathogen Pythium ultimum (Trow). Infection of plants by P. ultimum was assessed by observing symptoms of damping-off in seedlings and by microscopic observation of fungal hyphae and spores in seedling roots. Using P. ultimum as a test pathogen, comparison was made between the susceptibility of Zn accumulating seedlings of T. caerulescens with those of non-accumulating species of T. arvense and between seedlings of T. caerulescens grown from three seed collections of different zinc status. The seeds of the Zn-hyperaccumulating species germinated well up to the level of 30mg Zn mL^-1. The germination/damping-off rate increases/decreases with the increasing of Zn concentrations in the seeds of Zn-hyperaccumulating plants. Whereas, in non-accumulator the germination rate was decreased with increasing of Zn concentrations and not a single seed was germinated in presence of P. ultimum. In the three populations of T. caerulescens damping-off was manifested according to the concentration present in the seeds. In all of these experiments infection by P. ultimum was greatly reduced in the roots containing high concentration of Zn. The results confirm the hypothesis that heavy metal hyperaccumulation in these plants confers protection against attack by fungal root-pathogens.