A World Trade Organization panel has upheld a U.S. claim that Japanese quarantine measures against apples are too strict and violate WTO rules, trade sources said Wednesday.

The dispute settlement panel made the conclusion in a final report sent to the two countries. The report is expected to be made public next month.

Japan is set to file an appeal to the WTO Appellate Body, but it is unlikely that the panel's decision would be overturned. The decision will probably force Japan to change its plant quarantine rules.

The dispute involves quarantine measures against fire blight, a disease that causes infected apple trees to die.

Japan, which has no fire blight-related plant disease, requires U.S. exporters to provide evidence that the apple trees from which the fruit are picked for export to Japan are free of the disease for several years.

Japan also requires U.S. apple farmers to keep trees producing fruit for export at least 500 meters away from other apple trees.

The U.S. argues that the Japanese measures are too strict and breach WTO rules on plant quarantine. The U.S. based its claims on studies showing that mature apples do not carry the disease's causative agent.