Root vegetable producing sugar (4)
I believe the answer is:
beet
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">root vegetable producing sugar</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for beet that I've seen before include "Plant grown for sugar" , "An edible root plant" , "Root, maybe source of sugar" , "Source of food" , "E.g. chard, mangelwurzel" .)