How is it that these sensible posts are ignored by Duolingo for at least a year?
Tunda langu means "My (single piece of) fruit".
Matunda yangu means "My (pieces of) fruit."
Of course, in English, "my fruit" gives no clue as to which one is meant and I think the plural PIECES of fruit is the default interpretation for most people ... so yeah, it should definitely accept either tunda langu or matunda yangu.
DL is inconsistent with itself on the matter of "matunda". Up to this point in the course, it uses "matunda" to mean "fruit" in general as well as "pieces of fruit". So in this exercise, if one wishes to interpret "My fruit" as "my fruit in general", the correct translation is "Matunda yangu." If one interprets it as "my piece of fruit", then, of course, the answer is "Tunda langu".