Corn, soyabeans and wheat futures opened lower at the Chicago Board of Trade on Monday, with corn dropping for the seventh straight day, due to economic uncertainty following the massive earthquake in Japan, traders said. At 9:35 am CDT (1435 GMT), CBOT May wheat was down 5-3/4 cents at $7.13 a bushel, CBOT May corn was down 7 cents at $6.57-1/4 a bushel and CBOT May soyabeans were down 12 cents at $13.22-1/2 a bushel.