`"_______________"` promotes senescence and is found in high concentration in ripened fruits.

Answer

To answer the question, "_______________ promotes senescence and is found in high concentration in ripened fruits," we need to identify the correct phytohormone associated with these characteristics.

### Step-by-Step Solution:

1. **Understanding Senescence**: Senescence refers to the process of aging in plants, which includes the gradual deterioration of cellular functions leading to death.

2. **Identifying Phytohormones**: There are several phytohormones that play roles in plant growth and development, including:
- Auxins
- Cytokinins
- Abscisic acid (ABA)
- Gibberellins
- Ethylene

3. **Role of Ethylene**: Among these phytohormones, ethylene is known as the "aging hormone." It is specifically associated with the ripening of fruits and the promotion of senescence.

4. **Concentration in Ripened Fruits**: Ethylene is produced in high concentrations during the ripening process of fruits. This hormone not only promotes ripening but also induces senescence in plant tissues.

5. **Final Answer**: Therefore, the blank in the question can be filled with "Ethylene."

The complete statement is: "Ethylene promotes senescence and is found in high concentration in ripened fruits."