Regreein wheat was a type of food grain.
In 2370, Drofo Awa, the captain of a Xepolite Free Trader suspected to be delivering weapons to the Cardassians, pretended that his ship was carrying five kilotons of Regreein wheat husks. (DS9: "The Maquis, Part II")
The Star Trek Encyclopedia entry incorrectly talks about "Regrean wheat husks", in contradiction with the spelling in the script.