List and described at least $4$ factors for which crop variety improvement are done.

Factors for which crop variety improvement is done as listed below:-

1.Crop variety improvement improves the yield of plant and plant products.

2. It helps in imparting wider adaptability and greater resistance to both pests and climate.

3. Crop improvement also helps in developing desirable agronomic characters.

4. Shelf life of the crop also increases.