Grafting trees onto existing root systems is a common practice in nurseries for several reasons:

• Disease Resistance: Many fruit tree varieties are susceptible to certain diseases. By grafting a desired variety onto a rootstock that is resistant to these diseases, nurseries can create trees that are more likely to survive and produce healthy fruit.
• Adaptability: Different rootstocks have varying characteristics such as growth rates, soil preferences, and cold hardiness. By grafting a desired variety onto a rootstock that is well-suited to specific growing conditions, nurseries can produce trees that are more likely to thrive in a particular region.
• Dwarfing or Vigor: Some rootstocks have the ability to dwarf or increase the vigor of a grafted variety. This can be beneficial for growing trees in smaller spaces or for producing larger fruits, respectively.
• Early Fruiting: Certain rootstocks can induce earlier fruiting in grafted varieties, allowing growers to start harvesting fruit sooner.
• Propagation: Grafting is an efficient way to propagate and multiply desired varieties of trees. It allows nurseries to produce large numbers of identical trees from a single parent plant.

By carefully selecting the appropriate rootstock for a particular variety, nurseries can create trees that are better adapted to their environment, produce higher yields, and are more resistant to diseases and pests.