MF Global, the broker spun off from Man Group last year, has become the latest trading group to fall victim to a rogue trader after it admitted today that one of its staff had lost $141.5 million (£71 million) from unsuccessful bets on the direction of wheat futures.

The group said that Evan Dooley, who worked out of an office in memphis, tennessee, "substantially exceeded" the trading limits on his own account and had been dismissed instantly.

It blamed a failure in MF’s systems for permitting these "unauthorised" trades in the wheat futures markets in the early hours of Tuesday, which were liquidated within the next few hours.

Wheat prices have surged in recent days, jumping by 20 per cent on Monday in their largest one-day increase, to a record high, as Kazakhstan, one of the world’s largest exporters of grain, said that it would impose export tariffs to curb sales.

MF said that the loss represented about 6 per cent of the group’s equity, but emphasised that its capital position remained strong.

MF Global is the world’s biggest broker for options and futures, a contract to buy or sell a security at a specified time for an agreed price.

MF’s trading loss emerged barely a month after Société Générale revealed that Jérôme Kerviel, one of its traders, had lost €4.9 billion (£3.7 billion) from bets on European stock indices such as the CAC, DAX and EuroStoxx50.

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