Wheat's rally took its gains in a week above 14% in Paris, and 15% in London, as persistent fears for dry weather outplayed relief at a relatively strong official forecast for the French crop.

France's farm ministry, in its first harvest estimate, pegged France's soft wheat crop at 35.3m tonnes, down 2.5% on last year's production, but still above many analysts' estimates.

The figure is marginally higher than lobby group Coceral forecast two weeks ago, before concerns over dry weather in the European Union's biggest grain producer came to a head,

Pierre Begoc, executive director at Paris-based consultancy Agritel, told Agrimoney.com a 35.3m-tonne crop  would be "not too bad".

The ministry said its estimate reflected a yield decline of some 8% to 7.1m tonnes per hectare, more than offsetting a rise of 5% in plantings in a switch away from barley, which loses EU intervention support this season.

Investors fret

Nonetheless, wheat prices maintained their upward run, with Paris wheat for November delivery jumping 4.1% to E160.50 a tonne, the best for a nearest-but-one contract for 13 months.

London's November lot – again, the best-traded contract – added 4.4% to year high of £120.00 a tonne.

"People are worried about the damage being done to the wheat crop, particularly in France and Germany," a UK grain trader told Agrimoney.com.

"There are a number of very, very skittish shorts trying to take cover, and make sure they do not get completely shafted."

This level of volatility is considerably less common in Europe than in the Chicago markets, which attract greater weights of speculative money. Agrimoney.com has been unable to find a comparable run up in London wheat prices, in percentage terms, since 2007, as world prices were spiking.

A number of observers were maintaining forecasts of the French harvest below 35m tonnes, the trader added, viewing the French ministry's official estimate as "only one piece of the jigsaw".

Rapeseed boost

Mr Begoc added that it was as yet too early to piece together a forecast based on actual yields from the early stages of the French harvest, with results "different from one area to another one".

"Everything depends on the local conditions that look place in June," he added.

However, speaking from Kiev, he flagged the weakness of Ukrainian rapeseed yields, which were coming in about 1.4 tonnes per hectare, signalling a crop of some 1.4m tonnes, down 22% year on year.

"Europe will not be able to find in Ukraine and Canada enough rapeseed to fill its needs," he said, adding that the developments were "bullish" for prices.

November rapeseed stood 1.4% higher at E133.50 in Paris.

The European performances helped US wheat prices higher too, with Chicago's July wheat contract gaining 4.8% to $511.00 a bushel at one point.