There has been little research into the compatibility of commonly utilized apple rootstocks and VA-fungal types, and even less research regarding the effects of herbicides used in orchards, on the VAM symbiosis of apple trees. Studies demonstrated that early inoculation of young apple plants, prior to transplanting, results in healthy and vigorous plants with better growth and nutrition than uninoculated plants. We studied the efficiency of VA-fungal species and isolates on young apple rootstocks, produced by in vitro propagation. Mycorrhizal inoculation promoted plant growth, dry mass production and leaf P concentration. Mycorrhizal efficiency was associated with larger external hyphal network but showed no relation with the internal colonization. Despite the high P-fertility of the soil used, growth enhancement due to mycorrhizal inoculation was attributed to an improved P nutrition. / In a second experiment, the effect of herbicides currently used in orchards was tested on the mycorrhizal symbiosis. Paraquat, simazine and dichlobenil were applied to soil with mycorrhizal and non-mycorrhizal apple plants. Mycorrhizae increased herbicide toxicity in apple, as demonstrated by the greatly increased plant mortality. While both paraquat and simazine decreased spore germination in vitro, none of the herbicide treatments affected root colonization in soil. Effects on the photosynthetic rate, measured after herbicide application, indicated a physiological interaction between mycorrhizal colonization and dichlobenil, involved in the toxic response of apple plants.

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