Organic Farm Soil Improves Strawberry Growth But Does Not Diminish Spittlebug Damage

Soil microorganisms are central to the success of low-input agriculture. Among these microbes, arbuscular mycorrhizal fungi (AMF) are integral components of soil communities and are well known for facilitating nutrient uptake by plants. These root symbionts can alter tolerance and resistance of plants to pathogens, and there is mounting evidence that AMF can similarly affect plant-herbivore relations. A greenhouse experiment tested whether inoculation with soil containing AMF alters tolerance of strawberry plants to herbivory by a xylem-feeding insect, the meadow spittlebug Philaenus spumarius. Commercially produced, bare-root 'Ozark Beauty' strawberry plants (a day-neutral cultivar) were inoculated with organic farm soil containing AMF spores or with AMF-free soil filtrate and subsequently challenged with one of five herbivore loads. Inoculation with soil increased survival, flowering, runner production, and root and shoot mass. Twenty-four days of spittlebug feeding reduced leaf mass but the negative impact was small compared with positive effects of inoculation with soil containing AMF. Effects of both treatments were additive: compared with AMF-free filtrate, soil inoculum did not alter tolerance of the plant to this xylem-feeding herbivore but did increase plant productivity.