Colonization of Strawberry Roots by VA Mycorrhizal Fungi in Agroecosystems under Conventional and Transitional Organic Management

ABSTRACT

Mycorrhizal colonization of strawberry roots was studied for two agricultural management systems on the California central coast, one conventional and one in transition to organic. Low levels of VAM colonization early in the first year of the experiment may be the result of past management practices, which included conventional production of a non-mycorrhizal crop with high levels of phosphorus inputs. In the second year colonization levels were higher in the transitional organic plots. Annual use of a fumigant and a fungicide in the conventional plots was implicated with depleting the VAM inoculum reservoir and maintaining low colonization levels. Inoculation of organically managed plots with Glomus intraradices at the second planting did not change colonization levels. Soil analyses showed that available soil phosphorus levels remained high (range 62 to 101 ppm) in both treatments throughout the study. In both years colonization increased during the spring and summer harvest season, and it is hypothesized that the high phosphorus demand of strawberries during the reproductive growth stage may create a microzone of phosphorus depletion around roots, even in soil with high levels of phosphorus. If present, this depletion microzone would enhance the formation and potential benefits of mycorrhiza.