Relative growth rate is the measure of the ability of the plant to produce new plant material so it is also referred as

Answer

**Step-by-Step Solution:**

1. **Understanding Relative Growth Rate (RGR):**
- Relative growth rate is a measure of how effectively a plant can produce new plant material over time. It reflects the growth dynamics of the plant.

2. **Growth Analysis Index:**
- RGR is recognized as a widely used growth analysis index. It is derived from the growth of cell populations when resources such as light, space, and nutrients are not limited.

3. **Mathematical Representation:**
- The RGR can be expressed mathematically using differential calculus. It is defined as:
\[ RGR = \frac{1}{W} \frac{dW}{dt} \]
- Here, \(dW\) represents the change in dry mass, \(dt\) is the change in time, and \(W\) is the existing biomass.

4. **Interpreting the Formula:**
- The formula indicates that RGR is the increase in dry mass per unit of existing biomass over a specific time period. This reflects the efficiency of the plant in utilizing resources for growth.

5. **Conclusion:**
- Since RGR measures the ability of the plant to produce new material, it is also referred to as the "efficiency index."

**Final Answer:**
Relative growth rate is also referred to as the efficiency index.

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