Benomyl inhibits phosphorus transport but not fungal alkaline phosphatase activity in a Glomus-cucumber symbiosis

Short-term effects of benomyl on the arbuscular mycorrhizal fungus Glomus caledonium (Nicol. & Gerd.) Trappe and Gerdeman associated with Cucumis sativus L. were studied by measuring effects on fungal P transport and on fungal alkaline phosphatase activity. Mycorrhizal plants were grown in three-compartment systems where nylon mesh was used to separate a root-free hyphal compartment (HC) and a root + hyphal compartment (RHC) from the main root compartment (RC). Non-mycorrhizal control plants were grown in similar growth units. After 6 wk benomyl was applied to the plants in three ways: as soil drenches to RHC or HC, or as a spray to the leaves, Benomyl was added in three concentrations. Equal amounts of P-32 and P-33 were added to the HC and to the RHC respectively, immediately after the application of benomyl. Plants were harvested 4-6 d later. Hyphal transport of P-32 from the HC was inhibited when benomyl was applied to the HC at 10 mu g g(-1) soil, whereas the uptake of P-33 from RHC (roots + hyphae) was reduced only at the highest dose of application to the RHC (100 mu g g(-1) soil). In contrast to the marked reduction of benomyl on fungal P transport, the activity of fungal alkaline phosphatase inside the roots was unaffected by benomyl.