* TSX falls 51.32 points, or 0.40 percent, to 12,773.16 * Eight of the 10 main index sectors decline * Potash Corp drops 3.6 percent, has biggest index impact * Bombardier higher after contract win By John Tilak and Rod Nickel TORONTO/WINNIPEG, Sept 11 (Reuters) - Canada's main stock index declined on Wednesday as Potash Corp of Saskatchewan dropped after two days of gains and gold miners declined on continued signals that a diplomatic solution to the Syrian crisis was possible. Shares of Potash Corp and other producers of the crop nutrient potash fell after strong advances in the two previous sessions that were linked to optimism that Russian rival Uralkali could change strategy. Reports circulated on Monday that billionaire Suleiman Kerimov might sell his stake in Uralkali, leading to speculation about a renewed partnership between Uralkali and Belarusian potash producer Belaruskali that would support potash prices. But Uralkali said on Tuesday it had no plans to return to the trade alliance with Belarus, and the world's biggest nickel producer, Norilsk Nickel, said on Wednesday it had no interest in Kerimov's stake. Shares of Potash fell 3.6 percent and had the biggest negative influence on the index. The market wanted to believe that the Russians and Belarusians will reconcile "but that hasn't been proven just yet," said Stan Wong, vice president and portfolio manager at Macquarie Private Wealth. "Shorter term, the drama that's played out in these two countries is still going to keep fertilizer companies a bit under water," said Wong, whose portfolio includes Potash. Over the long run. Potash and other fertilizer companies will benefit from increasing grain consumption, especially in emerging markets, Wong said. The Toronto Stock Exchange's S&P/TSX composite index was down 51.32 points, or 0.40 percent, at 12,773.16. Eight of the 10 main sectors on the index were in the red. The materials sector, which has climbed since hitting a low in June, dropped 1.8 percent and was the biggest decliner among the major groups. In the materials group, gold-mining shares stumbled more than 1 percent as bullion prices fell as optimism about a diplomatic end to the Syrian crisis eroded gold's safe-haven appeal. Goldcorp Inc lost 0.9 percent to C$27.91, and Barrick Gold Corp shed 0.6 percent to C$18.95. Shares of energy producers were down 0.5 percent. Suncor Energy Inc fell 0.3 percent to C$36.50, and Enbridge Inc lost 1.8 percent to C$42.42. A consortium led by Bombardier Inc won a $288 million contract from Azerbaijan Railways to deliver signaling systems for an international corridor connecting Asia and Europe. Shares of Bombardier climbed 0.8 percent to C$4.99.