Two farmers, Manny and Juan, are cultivating different types of plants. Manny is cultivating Centotheca longilamina, while Juan is cultivating Centotheca malabarica.
Which farmer is cultivating Centotheca owariensis?
Manny is cultivating Centotheca longilamina, while Juan is cultivating Centotheca malabarica. 
So, the farmer who is cultivating Centotheca owariensis is not mentioned in the given information.
Therefore, we cannot determine which farmer is cultivating Centotheca owariensis based on the given information.