Section 117I. The commissioner of food and agriculture, in this section and in sections one hundred and seventeen J and one hundred and seventeen K called the commissioner, shall establish and promulgate official grades of potatoes packed or repacked within the commonwealth and may from time to time amend or modify such grades. Before establishing, amending or modifying any such grades, the commissioner shall consult with growers and shippers of potatoes relative to proposed grades, or upon written petition of fifty or more commercial potato growers, the commissioner shall, after reasonable notice, specifying the date, place and purpose of the proposed hearing, hold a public hearing for the purpose of obtaining information with a view to establishing, amending or modifying such official grades. The grades so established and promulgated shall include grades identical in name and requirements with all grades or standards of potatoes as promulgated from time to time by the secretary of agriculture of the United States and commonly known as the United States grades.