What type of fungi causes discoloration specifically in sapwood?

Sapstaining fungi are responsible for causing discoloration specifically in sapwood, which is the outer living layer of a tree that transports water and nutrients. This type of fungi thrives in the moisture-rich environment of freshly cut or improperly stored wood. The staining occurs when these fungi colonize the sapwood and produce pigments that create dark streaks or spots, leading to visual degradation of the wood.

On the other hand, brown rot and white rot fungi primarily cause more structural damage to wood rather than discoloration by breaking down the cellulose and lignin and reducing the wood to a crumbly state. Dry rot fungi, while also damaging, can result in significant decay and do not specifically target discoloration of sapwood like sapstaining fungi do. Thus, sapstaining fungi are uniquely identified for their characteristic staining effects on the sapwood, making them the correct choice in this context.