Effects of Mycorrhizal Inoculation of Day-Neutral Strawberries in an Organic Production System

University of Minnesota M.S. thesis. June 2018. Major: Applied Plant Sciences. Advisors: Mary Rogers, Emily Hoover. 1 computer file (PDF); viii, 80 pages.Biofertilizers are microbial inoculants used as replacements or supplements for the application of chemical fertilizers in agricultural systems. Rather than increase the amount of available nutrients in the soil, biofertilizers are intended to stimulate natural processes that can enhance nutrient uptake and plant growth. The present thesis considers the use of biofertilizers composed of arbuscular mycorrhizal fungi (AMF) to enhance organic day-neutral strawberry (Fragaria x ananassa) production in the Upper Midwest. The use of day-neutral strawberry cultivars, due to their long harvest window, could help growers in the region meet the rising demand for local, organic strawberries. Biofertilizers have been shown to enhance strawberry plant growth and yield, but there are relatively few studies that specifically examine biofertilizers in organic, day-neutral strawberries in field-grown conditions. To evaluate the efficacy of biofertilizers on day-neutral strawberry production in the Upper Midwest, we measured yield, plant growth, fruit quality, and mycorrhizal colonization in a two year study of ‘Portola’ strawberries inoculated with a commercially available mycorrhizal biofertilizer. We also studied the response of inoculated strawberry plants to an induced drought in field conditions, and the effect of different soil types on mycorrhizal colonization. The two-year field study indicated that inoculation with AMF biofertilizers did not lead to differences in yield, fruit quality, or plant size, nor did it lead to higher fungal colonization of strawberry plant roots. The low response to AMF inoculation was likely due to very high levels of available phosphorous in the field site. The induced drought had no effect on colonization or yield, but inoculated strawberries in different soil types did show very different levels of mycorrhizal colonization. Inoculated plants grown in low-phosphorous soils had much more mycorrhizal colonization than non-inoculated plants. Biofertilizers composed of AMF remain an important avenue of study, especially for growers attempting to grow strawberries in marginal soils. More research is needed to specifically focus on AMF biofertilizers in day-neutral production systems before recommendations can be made