Development of theLaccariabicolor(Maire) Orton basidiome in association with container-grownPinusstrobusL. seedlings was influenced by photosynthetic photon flux densities (PPFD). Three growth patterns were observed. At a PPFD of 330 μmol•m−2•s−1, basidiome growth was rapid, and complete development was achieved after 16 days. At a very low PPFD (20 μmol•m−2•s−1), the basidiome development ceased, although some residual growth was observed for a few days. At an intermediate PPFD (50 and 90 μmol•m−2•s−1), basidiome growth was less rapid than that observed at 330 μmol•m−2•s−1. Significant differences in the net photosynthesis of the host plant resulted in corresponding changes in basidiome biomass. The effect of basidiome removal on the photosynthetic response of the host plant was evaluated at three stages of basidiome development (2- to 4-, 6- to 8-, and 10- to 15-mm pileus diameter). At each developmental stage, removal of the basidiome induced a very rapid decrease in both net photosynthesis and stomatal conductance of the host plant. This decrease in net photosynthesis indicates that the growth and development of the basidiome are dependent on the host plant's current rate of net photosynthesis.