"variation is only the novel mutations that have occurred since that event" -> Mutations DO occur in Arabica
-> Option 1: Single species beans roasted - True
-> Option 2: Two species blended - True
-> Option 3: Novel mutations don't occur - False ✓
-> Option 4: Disease resistance variations - True
The answer is Option 3 - Due to its genetic make-up, novel mutations do not occur in the species Coffea Arabica.
Note: Finding the incorrect statement means looking for something that contradicts information in the passage!