In the late 17th and early 18th century the great violin maker Antonio Stradivari used a special wood that had grown in the cold period between 1645 and 1715. In the long winters and the cool summers, the wood grew especially slowly and evenly, creating low density and a high modulus of elasticity. Until now, modern violin makers could only dream of wood with such tonal qualities.
Similar wood can now be made available for violin making. The fungus species Physisporinus vitreus and Xylaria longipes can decay Norway spruce and sycamore—two important kinds of wood used for violin making—to such an extent that their tonal quality is improved. Unlike other fungus species, they gradually degrade the cell walls, inducing thinning; but even in the late stages of decomposition a stiff scaffold structure remains through which the sound waves can still travel directly.
The implementation of such biotechnological methods for treating soundboard wood could make it possible one day for violinists to afford instruments with the sound quality of a Stradivari.
This according to “Production of superior wood for violins by use of wood decay fungi” by Francis W.M.R. Schwarze, et al. (Journal of the Violin Society of America XXII/1  pp. 116-124). Above, a Stradivarius at the Palacio Real de Madrid. Below, a brief documentary on the process described by Schwarze.