Qatar Investment Authority and Swiss travel retailer Dufry are teaming up to bid for Italian travel retailer World Duty Free (WDF), which belongs to the Benetton family, two sources familiar with the matter told Reuters on Monday. "QIA and Dufry have a joint bid for WDF," said a senior banker in Doha familiar with the matter. He declined to give details but said the tie-up was a sign of a more conservative investment style adopted by the Qatari sovereign wealth fund recently; in the past, it might well have bid by itself. A second source confirmed the joint bid and said the deadline was now expected to be March 31, after a delay due to rival bidders - South Korea's Lotte Group and China's Sunrise Duty Free - asking for more time. QIA is estimated to have about $256 billion under management, according to the Sovereign Wealth Fund Institute. The Benetton family, which owns 50.1 percent of WDF via its holding company Edizione, is willing to give up control and favours a merger that would help the company cope with the rising costs of airport concessions, and also give the retailer more bargaining power with suppliers. WDF said in January it expected sales to be between 2.63 billion euros and 2.67 billion ($2.84-2.88 billion) this year, while adjusted earnings before interest, taxes, depreciation, and amortisation were expected at 279 million euros and 294 million. It reported sales of 2.4 billion euros and adjusted EBITDA of 289.7 million euros last year. Qatar's emir appointed ruling family member Sheikh Abdullah bin Mohamed bin Saud al-Thani as the new chief executive of the QIA last December, and there have been signs that Sheikh Abdullah is taking a more cautious approach to overseas acquisitions. The plunge in oil and natural gas prices appears to be one reason; although wealthy Qatar can cope relatively comfortably with lower export revenues, its state finances have been pressured. Also, the emir, Sheikh Tamim bin Hamad al-Thani, has urged Qataris in general to avoid lavish and excessive spending.