Corrupted Aura

Corrupted Aura raises the chance of the Corrupt mutation, x20. The wiki words the condition for Corrupt as During Corrupt Zen Aura, and separately lists Zen Aura as the weather that raises Tranquil fruit chance.

Corrupt can also come from any pet carrying the Corrupted mutation, and from the Corrupted Kodama when it harvests zen type crops. So this weather is the broad source, while the Kodama is the crop-specific one.