The fungal partner in mycorhizal association:

Explanation

Truffles are the correct answer because they form symbiotic relationships with the roots of trees in a mycorrhizal association, which benefits both the fungi and the host plant by improving nutrient absorption. Mushrooms, while also fungi, are not specifically known for forming these associations. Black bread mold is a saprophytic mold that decomposes organic matter and does not engage in mycorrhizal relationships. Morels are another type of edible fungus, but they are not primarily associated with such symbiotic interactions in the way truffles are.