Genetic and genomic insights into the successional patterns and reproduction methods of fire-associated Morchella

Abstract

Burn morels are among the earliest-emerging post-fire organisms in western North American montane coniferous forests, occurring in large numbers the year after a fire. Despite their significant economic and ecological importance, little is known about their duration of reproduction after a fire or the genetic and reproductive implications of mass fruiting events. I addressed these unknowns using post-fire surveys in British Columbia, Canada and Montana, USA in May/June of 2019. To assess fruiting duration, I collected specimens in second-year sites, where burn morels were collected the previous year, and identified them using DNA sequencing. Results demonstrated a predominant shift from burn to non-burn morel species, suggesting rapid changes in soil conditions and/or significant ecological differences between species. To address the implications of mass fruiting, I surveyed first-year post-fire sites, using whole-genome sequences to reveal the spatial extent of individuals and assess population genetic structure within and between sites for two species. Although gene flow appears more inhibited in Morchella sextelata than M. eximia, both species appear to disperse widely by ascospores and form populations characterized by large numbers of small individuals that persist as dormant structures between fires. My results will lead to a better biological understanding of these commercially and ecologically important mushrooms.