June 23 (Reuters) - Shares of Canada's Canopy Growth (WEED.TO) fell 6.5% on Friday after the pot producer posted a wider quarterly loss over the previous year and raised doubts about the company's ability to continue as a going concern. The Canadian cannabis industry remains challenged by systemic regulatory issues, continued battle with the illicit marijuana market and delays … [Read more...] about Pot producer Canopy raises going concern doubts, shares tumble