Quadrotriticale was a high-yield, perennial grain. Specifically, it was a genetically-engineered hybrid of wheat and rye with four distinct lobes per kernel, hence the "quadro-" prefix of its name, and was bluish in color. As of 2268, it was the only Earth grain able to grow on Sherman's Planet.
In 2268, Nilz Baris, the Federation Undersecretary in Charge of Agricultural Affairs, transported several tons of quadrotriticale to Deep Space Station K-7, intending to send it to Sherman's Planet for the purpose of developing it as an agrarian colony. He ordered Captain James T. Kirk, then commanding officer of the USS Enterprise, to protect the grain.
The grain was later discovered to be poisoned by the Klingons, through the assistance of their Intelligence operative, Arne Darvin, who had obtained a post as Baris's assistant specifically to carry out his mission, that of preventing the UFP from successfully developing Sherman's Planet, as the Organian Peace Treaty permitted. The poison consisted of a virus with which Darvin had impregnated the grain, which became an inert material in an organism's bloodstream when eaten; the amount of inert material was directly proportional to the amount of food, thus infected or not, that the organism ate, and within 48 to 72 hours, it prevented the organism from taking in enough nourishment to survive, essentially starving the organism to death. The discovery was made when untended tribbles got into the grain silos and ate the poisoned grain, and soon after died. (TOS: "The Trouble with Tribbles")
Quadrotriticale was not referred to in dialogue in "Trials and Tribble-ations," but was mentioned in the script's stage directions. A running gag in this epsiode is that James Kirk is the only person ignorant of what Quadrotriticale is!
According to the script pronunciation guide for "Business as Usual", this grain's name was pronounced as "QUAD-ro-TRIH-tih-kay-lee".