What is the purpose of crop variety improvement, and for which factors is it typically done?

 Crop variety improvement is done to produce crops of higher yield and improved quality which can be achieved by hybridization. 

Hybridization is the process of crossing two different species of the same genus. The crops produced by hybridization are of improved variety, also called genetically modified crops can be produced by the insertion of genes with desired traits. 

Crops are improved for higher yield, improved quality, pest resistance, climate resistance, etc.,