There seem to be 18 cultivars currently in ATP.
'Raja','Korean Giant','Yoinashi','Ichiban', 'Shinsui','Yakumo', 'Ya Li','Tsu Li','Siegyoku', 'Kikusui', 'Ishiiwase', 'Olympic', 'Shinko','Twentieth Century', 'Hosui', 'Shinseiki', 'Chojuro','Nijisseiki'.
A little off topic but chill hours might be something useful to maybe add to the DB in the future.