For union between stock and scion in grafting which one is the first to occur ?

Options

A. Formation of callus
B. Production of plasmodesmata
C. Differentiation of new vascular tissues
D. Regeneration of cortex and epidermis

Explanation

**Step-by-Step Text Solution:**

1. **Understanding Grafting**: Grafting is a horticultural technique that involves joining parts from two different plants so that they grow as one. The two main components in grafting are the stock and the scion. The stock is the part that provides the root system, while the scion is the part that is grafted onto the stock and is usually the part that produces the fruit.

2. **Identifying the Process**: The question asks which process occurs first during the union of the stock and scion in grafting. The options provided are:
- A) Formation of callus
- B) Production of plasmodesmata
- C) Differentiation of new vascular tissue
- D) Regeneration of cortex and epidermis

3. **Analyzing the Options**:
- **Formation of Callus**: This refers to the mass of parenchyma cells that develop around the wounded tissues of the plants at the graft union. It is the first response of the plant to injury.
- **Production of Plasmodesmata**: This involves the formation of channels between plant cells that allow for communication and transport of substances, but it occurs after callus formation.
- **Differentiation of New Vascular Tissue**: This occurs after the callus has formed and is part of the later stages of graft healing.
- **Regeneration of Cortex and Epidermis**: This is also a later stage in the healing process after the initial callus formation.

4. **Conclusion**: The first event that occurs at the junction of the graft union between the stock and scion is the formation of callus. This is crucial for the successful union of the two plant parts.

5. **Final Answer**: Therefore, the correct answer is **A) Formation of callus**.

---