“U.S. Commercial” consists of potatoes which meet the requirements of U.S. No. 1 grade except for the following:

1. (a) Free from serious damage caused by:

   1. (1) Dirt or other foreign matter;
   2. (2) Russet scab; and,
   3. (3) Rhizoctonia.
2. (b) Increased tolerances for defects specified in § 51.1546.