DOSE-RESPONSE RELATIONSHIPS BETWEEN 4 PESTICIDES AND PHOSPHORUS UPTAKE BY HYPHAE OF ARBUSCULAR MYCORRHIZAS

The effect of the fungicides carbendazim, fenpropimorph and propiconaz ole and of the insecticide dimethoate on plant P uptake via external h yphae of arbuscular mycorrhizal (AM) fungi was examined. Mycorrhizal p lants were grown in a two-compartment system where a root-free hyphal compartment was separated from the main root compartment by nylon mesh . After 5 weeks of plant growth external hyphae of the AM fungi had sp read throughout the hyphal compartment. At this time aqueous solutions of both P-32 and pesticide were added to the hyphal compartment. Resu lting soil pesticide concentrations covered a wide range with the aim of describing the dose-response relationships between pesticide concen tration and hyphal P uptake. Plants were harvested 6d after pesticide application. The amount of P-32 taken up into the plant was measured a s was hyphal length in the hyphal compartment. Carbendazim had the mos t negative effect, with concentrations above 0.006 mu g g(-1) leading to a sharp decrease in hyphal P uptake. Concentrations above 0.1 mu g g-l almost completely inhibited hyphal P uptake. This concentration is lower than the expected field concentration following carbendazim app lication at the recommended field rate. Hyphal P uptake was also negat ively affected by propiconazole but only at concentrations above 1 mu g g(-1). This corresponds to an expected field concentration of propic onazole after application of 10 times the recommended field dosage. Fe npropimorph and dimethoate had no negative effects on hyphal P uptake even when applied at concentrations of 125 or 46 mu g g(-1) respective ly. These concentrations are equivalent to expected field concentratio ns following pesticide applications at 100 times the recommended field rate. (C) 1998 Elsevier Science Ltd. All rights reserved.