According to Official Guinness Records,
The most watermelons split with a karate chop in one minute is 42, and was achieved by Ronald Sarchian (USA) on NBC’s Today in New York, New York, USA, on 5 September 2017.Ronald has set four previous Guinness World Records titles. All karate-chopped watermelon was collected by the Today Show culinary team and served to NBC employees at Rockefeller Center.
For a complete list of 2017 records, please visit 2017 Guinness Records in United States.