The crop where hybrid vigour has been utilised most is

1. Rice
2. Maize
3. Barley
4. Oat

The correct option is 2.
Maize, known in some English-speaking countries as corn, is a large grain plant domesticated by indigenous peoples in Mesoamerica in prehistoric times. The leafy stalk produces ears which contain the grain, which are seeds called kernels. Maize kernels are often used in cooking as a starch.