Russian President Vladimir Putin is set to host his Turkish counterpart Recep Tayyip Erdogan for bilateral talks on Wednesday in the Black Sea coastal city of Sochi; they last met on March 10 in Moscow.

Economic ties between the two countries had long been on a positive track until, as Putin put it, Turkey "stabbed Russia in the back" by shooting down a Russian fighter jet over the Turkish-Syrian border in November 2015. The Turkish leader initially said nothing, but eventually apologized for the incident a few months later in an effort to normalize relations with Moscow. Nonetheless, the once warm friendship has yet to completely recover.

'A few tomatoes'

Erdogan's visit to Moscow in early March did not deliver the hoped-for results: the lifting of an embargo on the export of tomatoes to Russia.

"They're not going to get away with this with a few tomatoes," said Putin after the jet was shot down.

Turkish vegetable exporters did suffer under the embargo; tomatoes had traditionally formed a large part of their shipments to Russia.

Russia has since loosened its restrictions on Turkish food exporters. Imports of citrus fruit, cabbage, cloves, stone fruits and onions are permitted again. But the embargo is still partly in place, banning the import of Turkish cucumbers, apples and pears. Turkish farmers say that the volume of agricultural exports is just 15 percent of what it was before the sanctions were introduced.

But Ankara wasn't prepared to just sit back and accept the sanctions. Russia also lost an important trading partner for agricultural goods after Turkey raised import tariffs, affecting Russian exports of corn, beans and sunflower oil. The tariffs hike ranged anywhere from 9 to 130 percent, effectively closing Turkey as a market for certain Russian products.

And Moscow felt the pinch: After Egypt, Turkey is its second-biggest importer of Russian grain and sunflower oil. A report on the Russian economy in April estimated that Ankara's actions cost Moscow some $1.5 billion (1.4 billion euros).

Assad's future a sticking point

But while normalizing trade relations seems like a relatively easy task, the war in Syria is much more complicated. Turkey and Russia, who have deployed military operations on the ground in the country, have different ideas about what Syria's post-conflict future should look like - most notably when it comes to the fate of President Bashar al-Assad.

Since the start of the war, Ankara has taken the view that Assad should step down as quickly as possible to clear the path for an inner-Syrian reconciliation. "As long as Assad is in power, there can be no solution for Syria," Erdogan said recently during an interview with Reuters news agency.

Russia stresses that it is not holding onto Assad. Erdogan says he has discussed the problem with Putin, who assured him that he is not acting as Assad's counsel. But in reality, Russia is keeping the Syrian leader in power and helping him to fight his armed opponents. Officially, Moscow sees no alternative to its course in Syria.

"Assad is the legitimate leader of the country, his army is fighting the rebels who control large parts of the republic," Dmitry Peskov, Putin's press spokesman, said recently. In Putin's view, Russia is supporting the fight against terrorism, including the so-called "Islamic State," which is why it would be absurd to insist that the Kremlin refrain from supporting Assad.