MOSCOW - Turkey’s worsening dispute with Russia over the downing of a Russian warplane is prompting Ankara to prepare to source vital food and energy imports elsewhere, underscoring the dispute’s potential to up-end lucrative trade ties. Turkish politicians have tried to ease tensions with Moscow after their air force shot down the Russian jet on Nov. 24, but the Kremlin has spurned their overtures, underlining the depth of its fury at what Vladimir Putin has called “a big mistake.” It banned imports of some Turkish foodstuffs as part of a sanctions package, and on Wednesday Russia’s defence ministry said it had proof that President Tayyip Erdogan and his family were benefiting from the illegal smuggling of oil from Islamic State-held territory in Syria and Iraq. Despite the rhetoric, Russia’s retaliatory measures have so far been relatively limited in scope - affecting only some fruit and vegetable imports for example. The two countries’ multi-billion dollar trade ties cover a wide range of sectors including tourism, energy, construction and food. In two key areas, grain and gas, Turkey is preparing back-up plans. On Wednesday, traders and analysts told Reuters Ankara was actively looking for alternatives to Russian grain because the spat had placed a question mark over future deliveries and put new deals on hold. Russia has not so far interfered with grain exports to Turkey, the largest buyer of Russian wheat, and vessels are departing Russian ports as normal apart from a few minor difficulties at some terminals. But traders in both countries say they fear that either Russia will restrict grain exports to Turkey or Ankara will limit deals with Moscow. “Turkish buyers remain worried about buying Russian commodities as no one knows what will happen and the fact is that Russia is still defiant and increasing tensions,” one trader in Turkey said. “I’m still worried that Turkey could impose sanctions on Russian goods in response.” In a related move, two sources told Reuters Turkey was preparing to cut imports of liquefied petroleum gas (LPG) - used to power everything from cars to household stoves - from Russia by a quarter next year. The disclosure follows news that Russia may adopt further punitive measures on Ankara, including freezing work on the Turkish Stream gas pipeline project.. Turkey has the most gas-powered cars in the world with 40 percent of its vehicles running on LPG. “Turkish firms are not simply worried about a reduction in LPG deliveries from Russia because of the current situation - they are already preparing for this,” one trader who works in the LPG market told Reuters. “It may be more expensive, but the process of how to ensure future deliveries from elsewhere is being worked out.”