Interaction between mycorrhization with Glomus intraradices and phosphorus in nursery olive plants

Mycorrhization of nursery plants with arbuscular mycorrhizal fungi (AMF) has become a usual practice in olive nurseries. Mycorrhizal associations increase plant tolerance to biotic and abiotic stresses after transplanting by improving root system structure and development. Nutrient fertilization is also desirable because roots are confined in a limited amount of soil in the nursery containers. Since the olive tree is a species with low phosphorus requirements, and AMF can affect root system development and nutrient uptake, it is of interest to study the possible interaction between both factors. Three different experiments with potted plants growing in a shade house, and one experiment under field conditions, were preformed using young olive plants to explore these questions. Inoculation with Glomus intraradices did not affect the phosphorus level in the plants but reduced shoot growth in plants growing in phosphorus-rich soil. When the substrate was a soil poor in phosphorus, shoot growth of AMF-inoculated plants was similar to the control but root development was greater. Mycorrhization also increased flower number and quality in 'Arbequina'. Shoot growth also was reduced when a sterilized substrate was used, suggesting that the use of natural soil is preferred. Since no mycorrhization effect was observed when inoculation was performed at the moment of transplanting to the field, inoculation during the nursery-growing period is recommended to improve plant quality for orchard establishment.