We always called them turnips. When I found out the large turnips seemed to be rutabagas I thought it made a dandy cheer, as when I was younger we heard about all sorts of cheers, some with nonsense syllables like sis boom bah.
How about rutabaga rutabaga rah rah rutabaga. It helps if you really like the taste. I read the Scots call them bashed neeps if you mash them
Somehow the four syllables, then two, then four, though not traditional for Japanese, works fine for Americans.