Sentence:  ‘<WSD>Shiro</WSD>' refers to the dense mat of fungal filaments that "Tricholoma Matsutake" forms in soil in association with pine roots and soil particles. It is considered that the amount of mycelia in "T.  matsutake" <WSD>shiros</WSD> is closely related to the amount of emerged "T. matsutake" fruiting body. 
Meaning of the word marked with <WSD> tags:  A mass of hyphae constituting the mycelium of certain fungi.