This is from Gilbert Krebs on the groaners listserv. I think it is one of the better variants on this theme.

When their mine became defunct, partners Smith and Jones decided to grow mushrooms in its cool, dark tunnels. Business prospered but Smith wanted all the profits, so he decided to kill Jones by planting some poisonous varieties in his partner’s section.

When. Jones found out, he had Smith arrested. Although the charge of attempted murder was dismissed for lack of evidence, the court did find Smith guilty of corrupting the morels of a miner.