BUENOS AIRES, May 29 (Reuters) - Oilseed crushers in Argentina's main grains hub Rosario will go on strike over wages on Wednesday, the general secretary of the local union told Reuters. The South American country is the world's No. 1 exporter of soyoil, which is used for cooking and in the booming biofuels industry, and of soymeal, used as animal feed. "As of the first shift tomorrow we will go on strike, with picketing at the entrances of the crushing plants," local union leader Pabl