Exposure to ammonia fumes may injure apples. The degree of injury depends on the length of exposure and on the concentration of the ammonia. The first symptoms appear as darkening of the tissues surrounding lenticels and wounds. In red varieties a chemical reaction changes the pigment from red to blue-black. The discoloration caused by a short exposure to a relatively low concentration of ammonia will disappear when the fruits are placed in an ammonia-free atmosphere. However, if the tissues are permanently injured, the skin turns brown at or around the lenticels (top photo). Small pits up to 1/8 inch in diameter may develop at the lenticels as moisture is lost from the injured tissues. Prolonged exposure even to a moderate concentration of ammonia will kill the outer layers of cells of the fruits, producing a uniform brown discoloration.
On Golden Delicious the first symptoms are olive-green areas around the lenticels. With increases in ammonia concentration or length of exposure, the lenticels blacken and the skin turns brown. The skin discoloration on Golden Delicious fades only slightly when the fruits are placed in an ammonia-free atmosphere.
Ammonia injury, Golden Delicious
Ammonia injury, Morgenduft