CHICAGO, May 28 (Reuters) - Chicago Board of Trade corn futures gained on Thursday as investor doubts over the prospects for a deal to reopen the Strait of Hormuz drove oil prices higher, supporting crops used as feedstock to make biofuel.

• Oil prices have been volatile in recent sessions as traders parse conflicting signals on the possibility of an end to the three-month Iran war and a potential re-opening of the Strait of Hormuz.

• Traffic through the maritime chokepoint remains at a small fraction of the pre-war level. O/R

• Chicago corn futures often track oil prices, as the grain is used as a feedstock for biodiesel.

• The U.S. Federal Trade Commission said on Thursday it has been investigating increased fertilizer prices following a spike due to the war in Iran.

• Soaring prices for fertilizer and fuel due to the conflict have pinched farmers as they plant crops such as corn and grapple with a resurgent drought in parts of the U.S. Plains. Some growers are facing a fourth straight year of shrinking margins.

• CBOT July corn CN26 ended 3-1/4 cents higher to $4.55-3/4 per bushel.