We were asked earlier this week about what the Arizal's opinion was on which forbidden fruit was on the Etz HaDaat. Does anyone know what it might be?
There is a view based on Midrash, gemara (Brakhot 40a) and Zohar that the fruit of the Etz HaDaat was the grape and that Noah planted grapes (Bereshit 9:20) upon leaving the Ark in an attempt to rectify the sin of the forbidden fruit.
Since the Ari was a major kabbalistic teacher, my guess is that he followed that explanation but I don't yet have a formal source in his writings
In more detail R Moshe Miller writes here
One maintained that the grapevine was banished from the Garden of Eden [i.e. it was the Tree of Knowledge, according to one of the views cited (Bereishit Rabbah 15:8 and Sanhedrin 70b)] and [Noah] planted it here [in the ground - outside of the Garden of Eden].
According to the opinion that the vine was banished together with Adam from the Garden of Eden, Noah intended to rectify the vine with which Adam had transgressed. However, instead of sanctifying the wine which he made from the grapes, he became drunk on it. He thus debased himself by repeating Adam's sin, as explained below. The sin of the Tree of Knowledge was that Adam drank the juice which Eve squeezed from its grapes.
Rabbi Shimon [bar Yochai] said: This verse contains the secret of wisdom. When Noah wished to examine the sin that Adam had committed with the intention of avoiding it himself and learning how to rectify it and the world, he was unable to [fathom its secret]. So he squeezed grapes in order to examine [the secret of] the vineyard.
The Zohar states that Eve squeezed grapes from the Tree of Knowledge and gave Adam to drink. (Zohar I, 36a, 267b) Ziv Hazohar explains that this refers to "external" or secular wisdom, i.e. wisdom other than the Torah, such as philosophy, which attempts to examine divine secrets by way of the intellect; or witchcraft, which attempts to harness the powers of impurity.