Thesis Defence: The effects of irrigation treatments on Tuber melanosporum extramatrical mycelium and the surrounding ectomycorrhizal fungal community in a British Columbia truffle orchard

Laura Rebecca Loverock, supervised by Dr. Daniel Durall, will defend their thesis titled “The effects of irrigation treatments on Tuber melanosporum extramatrical mycelium and the surrounding ectomycorrhizal fungal community in a British Columbia truffle orchard” in partial fulfillment of the requirements for the degree of Master of Science in Biology.

An abstract for Laura Rebecca Loverock’s thesis is included below.

Defences are open to all members of the campus community as well as the general public. Registration is not required for in person defences.

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ABSTRACT

The French black truffle is the prized fruiting body of the ectomycorrhizal fungus (EMF) Tuber melanosporum. International markets price the black truffle from 2000-4000 Euros per kilogram, leading to the cultivation of T. melanosporum on nearly every continent. Despite the high value and broad range of cultivated areas, little is known about how to optimize T. melanosporum growth or mitigate potential EMF competitors. This is particularly true in novel environments. I investigated the optimization of T. melanosporum biomass and assessed the overall EMF community in roots and soil in relation to differing levels of irrigation in a T. melanosporum – Quercus robur orchard in Vancouver, Canada. I applied three rates of irrigation from June to September 2021 and quantified the abundance of T. melanosporum DNA in the soil and the composition of the surrounding soil and root EMF community. During the study, which coincided with an extreme heatwave and moderate drought, irrigation treatments were maintained at high (- 30 kPa), moderate (- 80 kPa), or low levels (up to -260 kPa) of soil moisture. Soil samples were collected monthly at 50 cm and 100 cm from each tree for quantification of T. melanosporum DNA. The EMF community was sampled in August from the soil and mycorrhizal root tips found 50 cm from the tree. DNA of T. melanosporum was quantified using droplet digital PCR (ddPCR), whereas composition of the EMF community was determined by PacBio Sequel II sequencing. Generalized Additive Models revealed that the DNA abundance of T. melanosporum was highest under low-irrigation trees during the hottest and driest weeks, while the lowest abundance of T. melanosporum was in the high irrigation treatment. Overall, the abundance of T. melanosporum decreased with increasing water content. Irrigation did not affect the EMF community in roots or soil, but several dominant species were identified as potential competitors. To the best of my knowledge, this work represents the first North American trial involving T. melanosporum where a variable, such as irrigation, has been manipulated and is also the first application of DNA metabarcoding to a North American T. melanosporum orchard.