It's mentioned in his authorised biography that Tolkien had a personal liking of mushrooms, stretching as far back as his idyllic childhood days in Hall Green, Birmingham, the very same memories that supposedly inspired his writings about the Shire.
According to his younger brother Hilary Tolkien, his recollection is that a particularly loathsome farmer (that they nicknamed "the Black Ogre") once chased a young 'Ronald' Tolkien from his farm for the heinous crime of picking field mushrooms.
At the foot of the pool the dark waters suddenly plunged over the
sluice to the great wheel below: a dangerous and exciting place. . . .
Indeed, explorations could be made in many directions, though there
were hazards. An old farmer who once chased Ronald for picking
mushrooms was given the nickname “the Black Ogre” by the boys. Such
delicious terrors were the essence of those days at Sarehole...
J.R.R. Tolkien: A Biography
Decades later Tolkien confirmed that he was still extremely fond of wild mushrooms, of the very sort that might grow in the fields around Hobbiton.
I am in fact a Hobbit (in all but size). I like gardens, trees and
unmechanized farmlands; I smoke a pipe, and like good plain food
(unrefrigerated), but detest French cooking; I like, and even dare to
wear in these dull days, ornamental waistcoats. I am fond of mushrooms
(out of a field); have a very simple sense of humour (which even my
appreciative critics find tiresome); I go to bed late and get up late