Prior contact of <Emphasis Type="Italic">Pinus tabulaeformis</Emphasis> with ectomycorrhizal fungi increases plant growth and survival from damping-off

Pinus tabulaeformis (Chinese pine) is a widely planted conifer species in northern China and is used for soil and water conservation on the Loess Plateau. Due to its strong reliance on ectomycorrhizae and low survival rate from damping-off during seedling cultivation and in nurseries, we explored the early influence of three ectomycorrhizal fungi (Handkea utriformis, Suillus lactifluus, and Suillus tomentosus) on the growth, root morphological characters, root vitality, and survival of P. tabulaeformis seedlings from subsequent damping-off in a pot experiment. In addition, the in vitro suppression of three ectomycorrhizal fungi on the damping-off pathogen (Fusarium solani) was evaluated and observed using a scanning electron microscope. We found that all three ectomycorrhizal fungi could colonize more than 40% of the roots of P. tabulaeformis, promote plant shoot and root growth, increase the proportion of large-diameter roots, improve root vitality, and increase survival rates 3 months after inoculation. All three ectomycorrhizal fungi suppressed the growth of F. solani to a different extent in vitro. Ectomycorrhizal fungal hyphae proliferated and wrapped around the hyphae of F. solani when the hyphae encountered each other. The colonization rate of P. tabulaeformis roots was highly correlated with root vitality and root growth parameters, while the survival rate of P. tabulaeformis seedlings was highly correlated with the colonization rate of P. tabulaeformis roots, root vitality and growth. Our results suggest that early contact between P. tabulaeformis and ectomycorrhizal fungi could improve plant growth and resistance against damping-off.