Mycorrhizal fungi collected from the rhizospheres around different olive cultivars vary in their ability to improve growth and polyphenol levels in leeks

Authors: Malik, Nasir; Nunez, Alberto; McKeever, Lindsay; KUNTA, MADHURABABU - Citrus Center; Douds, David; Needleman, David

Submitted to: Journal of Agricultural Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/15/2016
Publication Date: 7/15/2016
Publication URL: http://handle.nal.usda.gov/10113/62937
Citation: Malik, N.S., Nunez, A., McKeever, L., Kunta, M., Douds, D.D., Needleman, D.S. 2016. Mycorrhizal fungi collected from the rhizospheres around different olive cultivars vary in their ability to improve growth and polyphenol levels in leeks. Journal of Agricultural Science. 8:1-10.

Interpretive Summary: Arbuscular mycorrhizal (AM) fungi are naturally occurring soil fungi that form a beneficial symbiosis with roots of most crops. Over two hundred mycorrhizal fungal species have been identified that can develop a symbiotic relationship with a wide variety of terrestrial plants. Generally, a mycorrhizal fungus can have a very large range of host plants but some exhibit specificity for certain hosts, and it is very plausible that a certain combination of a specific mycorrhizal fungal species with a specific plant cultivar could generate much better effects on plant growth and quality than other combinations. Our goal is to find combinations that perform best for plant growth and quality, and hence offer opportunities to improve production in our cultivation systems. This study was conducted to isolate different types of mycorrhizae from the rhizosphere of different olive cultivars to study which of these perform best in terms of improving plant growth and/or polyphenol production of a host plant (leek was our test plant) used under the controlled experimental system which could later be exploited for olive field studies. Olive cultivars grown in Texas were chosen for testing mycorrhizae associated with their roots. Results of these studies clearly show that AM fungi communities in the rhizosphere of cv Frantoio give the best results in terms of improving growth and quality (i.e. polyphenol levels) of leek plants.

Technical Abstract: Mycorrhizal fungus spores and propagules were collected from the soils in the vicinity of roots of five different olive cultivars. These mycorrhizal fungal communities were amplified in trap cultures and then their effect on the growth and polyphenol levels of leek plants was determined. All mycorrhizal fungal communities increased plant growth in leeks when compared to controls. In addition, mycorrhizal preparations from the roots of Frantoio and Manzanillo, significantly increase plant growth, in terms of plant height and dry weights, as compared to plants that were given mycorrhizal fungi 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 peeks were also higher in leek plants inoculated with mycorrhizal fungus from Frantoio roots when compared to plants inoculated with mycorrhizal fungus 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 fungal 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.