Genetic structure of Boletus edulis populations

Theme: Agriculture and Food Security

PhD project description: Boletus edulis is arguably the most important species of edible wild mushroom worldwide. Although it cannot currently be cultured, it is picked commercially in many areas of the UK and some areas have imposed bans to prevent over-harvesting. In this context, understanding how the species spreads and the local impact of harvesting is of great interest. Over the last decade, Bill Amos has assembled a large set of GPS located samples from Thetford Forest from areas that include heavily picked public areas, newly planted areas into which spread is occurring and unpicked areas in a military training site. In addition, samples have been assembled to give a broader context from across the UK and from European countries including France, Germany, Poland, Finland and Sweden.

The rotation project aims to use genetic markers (microsatellites, nine polymorphic loci already developed) to genotype approximately 400 samples in order to investigate the extent to which adaptation to the five main host trees is leading to the evolution of distinct strains. This work will be extended in several important directions to form the basis of a PhD thesis. First, it will look in detail at geographic sub-structure at a range of levels from tens of metres (nearby trees) to several kilometres (different woods same forest), hundreds of kilometres (different parts of the UK) and, finally, between different European countries. Within this aim will be an analysis of how local genetic diversity relates to available habitat density. A second aim is to understand more about how the species spreads.

Thetford Forest is a dynamic environment with active forest management. Two regions exist where active regrowth is occurring coincident with the new appearance of B. edulis. This provides an excellent opportunity to interrogate genetically where the new mycelial mats are coming from: have they simply spread from neighbouring mature woodland or have they arrived de novo through wind-blown spores. Some samples have already been collected but more fieldwork will be needed. In particular we will exploit root-tip sampling, a method that has already been shown effective in trials performed in collaboration with Dr. Bryn Dentinger (Kew). Root tip sampling allows more comprehensive sampling as well as sampling outside the fruiting season. Third, the project will look at temporal separation. B. edulis has an extremely long fruiting season, beginning as early as late July and continuing through until late December. Named species / sub-species already exist that appear to have evolved to exploit conditions earlier in the season, the so-called summer boletes. I will therefore analyse the genetic data for signatures of genetic separation in time as well as space. In addition to these primary aims, a range of other themes can be addressed, depending on the previous results. For example, if strong patterns of geographic separation are found a follow-up aim will be to test for the impact of natural selection by testing whether one or more markers display patterns at odds with the rest of the panel. The work will involve training in several important skills including taxonomy, bioinformatics, field sampling, molecular biology including genotyping, population genetics and statistics.

I will work with large datasets (microsatellite markers, herbarium records) and carry out statistical interrogation of relationships between environmental factors and population diversity. Later stages of the project may involve mathematical modelling of species spread.