Roughly 40 percent of U. S. rice exports have been negatively affected by what many experts consider to be their industry's worst crisis, a USA Rice Federation official said Friday. Speaking in Little Rock to the Arkansas Rice Research and Promotion Board, federation Vice President Bob Cummings discussed the damage caused to the $ 1. 3 billion U. S. rice export market after the U. S. Department of Agriculture's August revelation that traces of an unapproved, genetically engineered rice had been discovered in U. S. longgrain rice supplies.