Fig 1. Ectomycorrhizal compatibility and incompatibility between Suillus—Pinus species pairings.

(A) During a compatible EMF interaction, Suillus-inoculated roots develop characteristic ectomycorrhizas with short swollen (bifurcated) root tips with well-developed hyphal sheath and Hartig-net (observed in cross-sections of root tips, S1 Fig). Incompatible EMF interactions fail to establish mycorrhizae, with little or no fungal colonization, and are morphologically indistinguishable from un-inoculated (non-mycorrhizal) control roots (also shown). (B) Ectomycorrhizal compatibility between different species of Suillus and Pinus measured as a proportion of EMF root tips versus total bare root tips (n≥3). Tukey test was used to test significance across Pinus species within a Suillus species (P<0.05). Means marked by the same letters were not significantly different. The complete list of fungal cultures and spore prints used is listed in S3 Table.