According to Official Guinness Records,
The most watermelons on a single watermelon plant is 131 and was achieved by Stanley Agricultural Group Co., Ltd. and Zhengzhou Zhengyan Seed Technology Company Limited (both China) on the set of CCTV-Guinness World Records Special in Zhengzhou, Henan, China on 31 July 2016. It was an outdoor attempt for CCTV-Guinness World Records Special. The watermelon plant is a new high-yielding variety called Tianlong 1508.
For a complete list of 2016 records, please visit 2016 Guinness Records in China.