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 Glo mus caledonium (Nicol. & Gerd.) Trappe and Gerdeman associated with Cu cumis sativus L. were studied by measuring effects on fungal P transpo rt and on fungal alkaline phosphatase activity. Mycorrhizal plants wer e grown in three-compartment systems where nylon mesh was used to sepa rate a root-free hyphal compartment (HC) and a root + hyphal compartme nt (RHC) from the main root compartment (RC). Non-mycorrhizal control plants were grown in similar growth units. After 6 wk benomyl was appl ied 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. Equa l amounts of P-32 and P-33 were added to the HC and to the RHC respect ively, immediately after the application of benomyl. Plants were harve sted 4-6 d later. Hyphal transport of P-32 from the HC was inhibited w hen benomyl was applied to the HC at 10 mu g g(-1) soil, whereas the u ptake of P-33 from RHC (roots + hyphae) was reduced only at the highes t 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 o f fungal alkaline phosphatase inside the roots was unaffected by benom yl.