THE EFFECT OF FUNGICIDES ON VESICULAR-ARBUSCULAR MYCORRHIZAL SYMBIOSIS .2. THE EFFECTS ON AREA OF INTERFACE AND EFFICIENCY OF P UPTAKE AND TRANSFER TO PLANT

Two experiments were conducted under controlled environmental conditio ns to determine the effects of the three fungicides, Benlate(R), Aliet te(R) and Ridomil(R), on efficiency of P uptake from the soil and tran sfer across the living plant-fungal interface of onion plants (Allium cepa L.) associated with Glomus sp. 'City Beach' (WUM 16). P applied t o the soil did not apparently increase the rate of transfer (flux) of P to the plant via the fungal partner of the mycorrhiza. Benlate reduc ed P inflow and transfer across the interface in one of the experiment s. The rate of P uptake per m living external hyphae was not affected but, as development of living external hyphae in the soil was reduced, the contribution of the fungus to P uptake was small. Aliette reduced growth of both shoots and roots, but apparently increased the accumul ation of P in the tissues compared with controls. Ridomil reduced P in flow per m of root and P uptake per m living external hyphae, but had no effect on the rate of P transfer across the interface. This led to a reduction in the overall contribution of the fungus to P nutrition.