Prices for top-quality spring wheat have jumped by 90 per cent in the past month and a half, boosted by a scramble by corporate consumers to secure scarce grain and speculative buying by investors.

A surge on Friday in prices for wheat used in bread to an all-time high of $19.88 a bushel – the highest yet paid for any wheat contract and a three-fold increase from a year ago – prompted the US baking industry to call for wheat exports to be curtailed.