Introduction
Advantages:
-Plants of good quality are introduced.
-Crops with high yielding capability are introduced.
-It enables a country to add to an existing number of crops.
Disadvantages:
-The introduced crop can introduce new disease to the new country.
-The  introduced crop may not adapt well to the new environment.

Selection
Advantages:
-Crops of better quality are selected
-Crops that cannot adapt to the environment are discarded.
-Breeds with high yielding ability are selected
Disadvantages:
-Selection cannot create variability
-It is tedious and time consuming.