Certainly no good reasons that are known.
I imagine religions as incorporating some folk wisdom whose origins are then lost and mutated.

...but now here's another example of ridiculous prohibitions perhaps having some practical result: "The cucumber mosaic virus has one of the broadest host ranges of any of the tomato viruses. The disease affects a number of important vegetables and ornamentals including tomato, pepper, cucumber, melons, squash, spinach, celery, beets, and petunia." -thanks google.

Dare we ask what the punishment is for rubbing cucumbers up against the tomatoes? Probably way out of proportion to the crime of spreading powdery mildew (though there probably were times in history when food was much more important than today).

~SA

Pyrolysis creates reduced carbon! ...Time for the next step in our evolutionary symbiosis with fire.