Study of Fruit Growth Stages and Construction of Sigmoid Growth Curve

Title: Measurement of fruit growth over time and identification of key physiological changes

1. Objectives

                                I.            To study different stages of fruit growth from fruit set to maturity.

                             II.            To measure fruit growth parameters (size/weight) at regular intervals.

                          III.            To plot the sigmoid (S-shaped) growth curve of the fruit.

                          IV.            To relate each growth phase to key changes such as cell division, cell enlargement, and biochemical development.

2. Principle

Most fruits show a sigmoid (S-shaped) growth pattern when fruit size or weight is plotted against time after fruit set. Growth is not uniform because fruit development happens in phases:

Phase I: Cell Division Phase (Early rapid growth)

• Ø  High cell division rate (increase in cell number).
• Ø  Fruit is small but grows quickly in number of cells.
• Ø  Strong dependence on hormones like auxin, gibberellin, cytokinin.
• Ø  High metabolic activity; tissues are soft and actively differentiating.

Phase II: Cell Expansion / Elongation Phase (Middle growth)

• Ø  Cell division slows, but cells increase in size by water uptake and vacuole expansion.
• Ø  Fruit weight increases faster (especially fresh weight).
• Ø  Accumulation of starch, organic acids, structural components.

Phase III: Maturation Phase (Growth slows; quality builds)

• Ø  Increase in dry matter, sugars, color pigments.
• Ø  Seeds become physiologically mature.
• Ø  Pre-ripening changes begin (varies by fruit type).

Note: Many fruits (e.g., apple, mango, guava) show a single sigmoid curve. Some fruits (e.g., peach, plum, cherry, grape) show a double sigmoid curve (Phase II lag corresponds to pit hardening/seed development).

3. Sigmoid Growth Curve (Diagram to draw in record)

Plot: X-axis = Days after fruit set (DAFS) and Y-axis = Fruit weight (g) or diameter (mm)

4. Materials Required

• Ø  Selected fruit crop plants (same variety, similar canopy position)
• Ø  Tags/labels + marker (for marking fruit set date)
• Ø  Measuring instruments:
• Ø  Vernier caliper / measuring tape (diameter/length)
• Ø  Electronic balance (fresh weight)
• Ø  Hot air oven (for dry weight if available)
• Ø  Penetrometer (firmness, optional)
• Ø  Refractometer (TSS, optional)
• Ø  Titration setup for acidity (optional)
• Ø  Notebook / record sheet / graph paper

5. Experimental Procedure

A. Tagging (Day 0)

Identify fruit set stage (just after fruit set, small marble stage depending on crop).

Tag and label fruits with:

Date of fruit set

Fruit number (F1, F2…F20)

B. Periodic Observation (Every 7 days is standard)

At 7-day intervals, record:

Fruit length (mm)

Fruit diameter (mm)

Fruit fresh weight (g) (if destructive sampling is allowed)

Optional: firmness, TSS, acidity

Two ways to sample: Non-destructive: measure length/diameter of the same tagged fruits each week. Destructive: harvest 3–5 fruits each week for fresh weight, dry weight, TSS, acidity (more accurate for physiology).

C. Dry Weight (Optional but very good)

Slice fruit sample, dry at 65–70°C in hot air oven until constant weight.

Record dry weight (g).

D. Plotting the Curve

Compute weekly mean values (average).

Plot:

Time (DAFS) vs Diameter (mm) or Fresh weight (g)

Draw the S-shaped sigmoid curve and label Phase I, II, III.

6. Result

The fruit showed a sigmoid growth pattern when plotted against time after fruit set. Early growth was dominated by cell division, mid growth by cell expansion, and late growth by maturation and quality development. The curve clearly distinguishes growth phases and correlates with physiological and biochemical changes occurring in the fruit.

7. Precautions

• Tag fruits correctly and record fruit set date accurately.
• Select fruits of similar exposure and avoid shaded/damaged fruits.
• Use same measurement points (equatorial diameter) every time.
• Handle fruits gently to avoid bruising (especially during firmness testing).
• If doing destructive sampling, keep sample size consistent each week.

8. Assignments

1. What is a sigmoid growth curve?
2. What dominates early fruit growth: cell division or cell expansion?
3. Why does growth rate slow near maturity?
4. What is double sigmoid growth? Give one example fruit.
5. Why is dry weight important in fruit development studies?
6. What hormonal changes support early fruit growth?