Mycorrhizal Fungi Collected from the Rhizospheres around Different Olive Cultivars Vary in Their Ability to Improve Growth and Polyphenol Levels in Leeks

Mycorrhizal fungus spores and propagules were collected from the soils in the vicinity of roots of five different olive cultivars. These mycorrhizal fungus communities were amplified in trap cultures and then their effect on the growth and polyphenol levels of leek plants was determined. All mycorrhizal fungus communities increased plant growth in leeks when compared to controls. In addition, communities from the roots of Frantoio and Manzanillo significantly increased plant growth, in terms of plant height and dry weights, as compared to plants that were given mycorrhizal fungus collected from cultivar Mission. Plants inoculated with mycorrhizal fungus from Frantoio also had an increase in 14 polyphenols compared to uninoculated plants. A majority of polyphenol peaks were also higher in leek plants inoculated with mycorrhizal fungi from Frantoio roots when compared to plants inoculated with mycorrhizal fungi from other olive cultivars. The affected polyphenols were identified by mass spectrometry and were mostly found to be derivatives (e.g., pentose, hexose, malonyl, feruyl, and coumaroyl) of quercetin, kaempferol, and apigenin; four remained unidentified. Molecular fingerprinting of mycorrhizal fungus communities from different olive cultivars indicated that fungi of the family Gigasporaceae were a major component of inocula obtained from Frantoio and Manzanillo roots, which were better performers in terms of plant growth and polyphenol content. Mycorrhizal fungi from cv Mission roots were relatively poor performers and were dominated by the mycorrhizae of the family Glomeraceae, specicifally the genus Rhizophagus.