Nine fungicides, 3 nematicides and 5 insecticides/acaricides were incorporated into the pot cultures of the VAM fungus Glomus fasciculatum in order to study their effect on the mycorrhizal association and the contaminant organisms. All the pesticides were found to be deleterious to VAM at the recommended level. Captan and carbofuran, at half the recommended level (125mg and 144.5mg respectively/2.5 litre of the substrate mix), increased significantly the percentage root colonization, extra-matrical chlamydospore number and inoculum potential. Captan and carbofuran at this level also significantly suppressed the contaminant fungi and nematodes in the pot cultures of G. fascieulatum. The insecticides/acaricides formothion and malathion at half the recommended level, had no deleterious effect on G. fasciculatum but suppressed mites and collumbola in pot cultures.

A field trial was conducted to study the response of sunflower (Helianthus annuus L.) to different phosphorus levels (16, 24 or 32 kg P ha -1) and inoculation with vesicular-arbuscular mycorrhizal fungus, Glomus fasciculatum on vertisol during summer 1993. At the vegetative stage of sunflower, percent mycorrhizal root colonization, spore count, dry biomass and P uptake did not differ significantly between inoculated and uninoculated control plants. However, at later stages (flowering and maturity) percent root colonization, spore count, total dry biomass and total P uptake were significantly higher in inoculated plants than in uninoculated control plants. The total dry biomass, P content and seed yield increased with increasing P level in uninoculated plants, whereas no significant difference was observed between 16 and 32 kg P ha -1 in inoculated plants. The positive effect of mycorrhizal inoculation decreased with increasing P level above 16 kg P ha -l, due to decreased percent root colonization and spore count at higher P levels.

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