Isolation by landscape in populations of a prized edible mushroom Tricholoma matsutake

Tricholoma matsutake, a wild edible ectomycorrhizal mushroom, is revered for its distinguished flavor and iconic significance. Here, we test for landscape effects on T. matsutake gene flow and population structure in the Eastern Himalayas. Using single-nucleotide polymorphic (SNP) DNA markers, isolation by distance patterns were tested on eight populations within and between watersheds. We find that high, treeless ridgelines are effective barriers to gene flow, even at distances less than 65 km, whereas populations located within watersheds are structured at greater distances. Mantel tests demonstrated a significant positive correlation between F (st) and a "landscape distance" measured as the shortest distance between population pairs below treeline r = 0.574, P = 0.002, whereas strict euclidian distances do not correlate. AMOVA analysis revealed significant partitioning with 91% of the genetic variance found within populations and 7% found between watersheds, indicative of sexually recombining populations with limited gene flow between watersheds. We show that landscape is an important determinant of air-dispersed ectomycorrhizal species population structure in heterogeneous landscapes.