Effects of systemic fungicides on vesicular-arbuscular mycorrhizal infection and plant phosphate uptake

The effects of two systemic fungicides on vesicular-arbuscular mycorrhiza were investigated with a view to using them in the study of mycorrhizal phosphate uptake. Formation of mycorrhiza in clover roots was prevented by soil drenches of benomyl and thiophanatemethyl and the spread of established infections was halted. Immersion of fungal inoculum in suspensions of the fungicides reduced infectivity. However clover plants grown in benomyl-treated soil did not retain enough fungicide to affect the amount of infection after transplanting into benomyl-free soil. Benomyl and thiophanate-methyl soil drenches reduced phosphate uptake of inoculated onion and strawberry plants when grown in irradiated soil, but not in unsterile soil. The short term uptake of radioactive 32P was reduced by benomyl but the results were variable and further work is required to improve the technique. RESP-7749