Establishment, persistence, and spread of a commercial arbuscular mycorrhizal fungal inoculant in viticulture

Arbuscular mycorrhizal (AM) fungi are a group of ecologically important fungi that associate with the majority of land plants and can increase plant uptake of phosphorus and nitrogen. Optimizing the interaction between crop plants and AM fungi by increasing AM fungal abundance or adding more beneficial strains through “biofertilizers” containing AM fungi has been proposed as a means of improving agricultural phosphorus use efficiency. However, the benefit from “biofertilizers” in the field is often variable and context-dependent, and their use may introduce strains that are not native to the system, potentially resulting in invasion by foreign AM fungi. In this thesis, I examine the performance of a commercial AM fungal inoculant in grapevine at a vineyard in West Kelowna, BC. The vines were inoculated in 2013 in through three timing strategies designed to test the influence of priority effects and inoculum abundance on inoculant establishment. Each year from 2013-2017, vine growth, productivity, and mortality were recorded. Using soil cores obtained before and after planting, as well as from surrounding non-inoculated areas, I determined the abundance of the inoculant in the soil during each year using a specific digital droplet PCR assay. I found that the inoculant was present prior to inoculation but did not establish as a result of any inoculation strategy, and consequently, inoculated and non-inoculated vines displayed equivalent growth, survival, and productivity. Without successful establishment, I was not able to examine the spread and persistence of the inoculant as a result of introduction, although a background population of the strain was detected each year. While an exact cause of the lack of establishment could not be determined, the soil phosphorus levels were notably high and root trimming may have interfered in the Pre-inoculated timing. This work highlights the likelihood of establishment failure, which is common in both greenhouse and field settings and is a major barrier to the use of these products. Also, many studies of the benefit of AM fungal inoculants do not quantify the abundance post-inoculation, which is important to determine whether the inoculant established.Arts and Sciences, Irving K. Barber School of (Okanagan)Biology, Department of (Okanagan)Graduat