What fruit is grown the most in the world?

Just to confuse the issue further http://www.westfalia-separator.com/en/news/download/digest/digestse1e.pdf claims that the banana is the most grown fruit in the world although some people may refute that as it is really a herb.

Depends what is meant by "most".

If we're going by tonnage:

This is a tricky question because it all depends what is defined as a fruit. For example, tomatoes are technically fruit, but are often classified statistically as vegetables.

The statistics also appear to be a little vague.

Wiki's top 10 by tonnage:

Watermelon 104,472,354 2011
Banana 102,000,000 2010
Orange (fruit) 68,500,000 2008
Grape 67,221,000 2009
Apple 64,255,520 2008

https://en.wikipedia.org/wiki/List_of_world_production#Fruit

Statista says (in tons):

Bananas 106m 2013
Apples 80m 2013
Grapes 77m 2013
Oranges 71m 2013

They don't even list watermellon.

http://www.statista.com/statistics/264001/worldwide-production-of-fruit-by-variety/

Soooo... Bananas or Watermellon would be my answer, depending on the specific data set and year being looked at.