Watermelon has the highest concentration of citrulline. The rind of the melon contains the most citrulline but it is found throughout. Different species of watermelon have varying amounts.

Cucumbers, pumpkin, some melons and certain varieties of gourds also have smaller amounts of citrulline.

5000mg Arginine and (250-1000)mg Citrulline

Watermelon - especially watermelon juice - contains high levels of readily accessible citrulline.

From wikipedia

The amino-acid citrulline was first extracted from watermelon and analyzed.[8] Watermelons contain a significant amount of citrulline and after consumption of several kg, an elevated concentration is measured in the blood plasma;

Citrullus is the latin word for watermelon. The rind of watermelon is known as a natural source of citrulline. Citrulline Malate seems to increase the energy and performance of the human body. It is widely used among bodybuilders, but also in clinical settings to treat fatigue, muscle weakness and dementia.

The amino acid citrulline was found in watermelon.

The nutritious acids folate, niacin, and pantothenic acid are also found in watermelon.