Wiktionary gives the following etymology of the word "арбуз" (watermelon):
From Turkic. Compare Ottoman Turkish خربز (harbüz), خربزه (harbüze), Tatar карбыз (qarbız), Bashkir ҡарбуз (qarbuz), Turkish karpuz. Ultimately from Persian خربز (xarboz).
Some other Slavic nations seem to have been more resistant to the Turkic influence:
Slovak: Dyňa červená
My question is this: What is the indigenous Russian word for a watermelon, and can it be used in modern Russian?
For example, if I write a fairy tale in Russian about a watermelon, I will use the original Russian word in order to make the fairy tale sound truly Russian.
P.S. By "indigenous Russian word," I mean a word of Slavic origin that was the main Russian word for a watermelon before the word "арбуз" became such. Here, the adjective "Russian" refers to the ethnic group forming the core of the Russian nation - specifically, the people who lived in and around Moscow within a reasonable distance and shared the same language and culture.
For example, I recently asked what is the indigenous Russian word for a wild boar, and got the answer "вепрь." I am now asking for the same thing for a watermelon.
If there was no indigenous Russian word for a watermelon, then stating this makes a valid answer.