The selection of the most effective arbuscular mycorrhizal (AM) fungi for growth enhancement of citrus cultivars used as rootstocks was the first step toward development of an AM inoculation system in citrus nurseries in Spain. AM fungi were isolated from citrus nurseries and orchards in the major citrus-growing areas of eastern Spain. The most common AM fungi found in citrus soils belonged to Glomus species, and G. mosseae (Nicol. & Gerd.) Gerdemann & Trappe and G. intraradices Schenck & Smith were the AM fungi most frequently associated with citrus roots. The most effective fungus for growth enhancement of citrus rootstocks was G. intraradices . Significant differences in mycorrhizal dependency among rootstocks were confirmed. Sour orange ( Citrus aurantium L.) and Cleopatra mandarin ( C. reshni L.) were more dependent than Troyer citrange [ C. sinensis (L.) Obs. × Poncirus trifoliata (L.) Raf.] and Swingle citrumelo ( C. paradisi Macf. × P. trifoliata ). Moreover, several inoculation systems for plant production were evaluated for their effectiveness in promoting root colonization of the rootstock cultivars.

This paper reports the effects of inoculation with arbuscular mycorrhizal fungi on early plant development, field establishment, and crop yield of the olive (Olea europaea L.) cultivar Arbequina. The response of olive plants to the fungi Glomus intraradices (Schenck and Smith) and G. mosseae (Nicol.& Gerd.) Gerdemann & Trappe in different potting mixes was studied in two different nursery experiments. Pre-inoculation with selected arbuscular mycorrhizal fungi prior to transplanting in the field improved plant growth and crop yield up to three years after inoculation. G. intraradices was more efficient at promoting plant growth than both G. mosseae and the native endophytes present in the orchard soil. Inoculation at the time of transplanting enhanced early plant growth in all the field situations studied. Diminishing mycorrhizal effects over time resulted from natural colonization of noninoculated seedlings and related to the native arbuscular mycorrhizal (AM) fungal population of the field soil. Early inoculation of olive seedlings enhances early plant development and crop productivity of olive trees.