Growth And Development of Horticultural Crops
1. Growth and Development - Definitions
Growth - Growth is the irreversible increase in size, volume, dry weight, or cell number of a living organism due to metabolic activities.
It represents the initial and essential phase of plant life involving an increase in size and biomass.
Processes involved
- Cell division (mitosis) in meristematic tissues
- Cell elongation through cell wall loosening and vacuole expansion
- Increase in dry matter due to photosynthesis and nutrient uptake
Cellular and physiological basis
- DNA replication and protein synthesis
- Increased metabolic activity
- Uptake of water, minerals, and assimilates
➡ Key characteristics
- Quantitative (measurable)
- Irreversible
- Results from cell division + cell enlargement
- Requires energy, nutrients, water, and hormones
📌 Example: Increase in shoot length, root mass, leaf area.
Development - Development is the sum total of growth and differentiation, including morphogenesis and maturation, leading to the formation of a complete and functional plant body.
Levels of development
- Cellular level: tissue specialization
- Organ level: root, stem, leaf, flower formation
- Whole plant level: vegetative → reproductive transition
Regulating factors
- Genetic control (developmental genes)
- Plant hormones (auxin, cytokinin, GA, ABA, ethylene)
- Environmental cues (light, temperature, photoperiod)
➡ Key characteristics
- Qualitative
- Time-dependent and stage-wise
- Includes growth + differentiation + morphogenesis + senescence
- Leads to functional specialization
📌 Outcome: Establishment of plant form, structure, and function over time.
📌 Example: Vegetative phase → flowering → fruiting → senescence.
Differences Between Growth and Development
| Aspect | Growth | Development |
|---|---|---|
| Nature | Quantitative | Qualitative |
| Measurement | cm, g, cell number | Stages, form, function |
| Reversibility | Irreversible | Sequential |
| Includes | Cell division & enlargement | Growth + differentiation |
| Example | Increase in plant height | Flower formation |
2. Parameters of Growth and Development
Growth is analysed using measurable parameters that describe plant performance and productivity.
A. Growth Parameters
1. Absolute Growth Rate (AGR) - Increase in plant size per unit time.
AGR = (W2 - W1) / (t2 - t1)
Where: (W1, W2) = Dry weight at time (t1, t2)
📌 Indicates actual gain, not efficiency.
2. Relative Growth Rate (RGR) - Growth per unit existing biomass per unit time.
RGR = (ln W2 - ln W1) / (t2 - t1)
📌 Important for young plants where growth is exponential.
3. Net Assimilation Rate (NAR) - Rate of dry matter accumulation per unit leaf area.
NAR = Increase in dry weight / (Leaf area × time)
📌 Indicates photosynthetic efficiency.
4. Leaf Area Index (LAI) - Ratio of total leaf area to ground area.
LAI = Leaf area / Ground area
📌 Determines light interception and yield potential.
B. Developmental Parameters
- Time to flowering
- Number of nodes before flowering
- Duration of vegetative & reproductive phases
- Physiological maturity
- Fruit maturity period
- Senescence timing
📌 Used mainly in phenological studies of horticultural crops.
3. Growth Dynamics
Growth dynamics describe the pattern and rate of growth over time.
Growth Curve (Sigmoid Curve)
Plant growth usually follows a sigmoid (S-shaped) curve when plotted against time.
Phases of Growth Dynamics
1. Lag Phase
- Cell division initiates
- Slow growth
- Enzyme synthesis and metabolic activation
2. Log (Exponential) Phase
- Maximum rate of cell division and elongation
- High RGR and NAR
- High sensitivity to nutrients & hormones
3. Decelerating Phase / Transitional Phase
- Resource limitation begins
- Reduced meristematic activity
4. Stationary Phase
- Growth plateaus
- Cells differentiate
- Leads to maturation and senescence
4. Morphogenesis
Definition: Morphogenesis is the development of form and structure in plants, controlled by genetic information and regulated by hormones and the environment.
📌 It answers: “Why does a leaf become a leaf and a root become a root?”
Components of Morphogenesis
1. Cell Division
Occurs in meristematic regions; determines cell number.
2. Cell Enlargement
Increase in cell size via vacuolation; cell wall loosening (role of auxin).
3. Cell Differentiation
Formation of specialized cells (e.g., xylem, phloem, mesophyll).
4. Pattern Formation
Spatial organization of tissues and organs; controlled by positional information.
Role of Plant Growth Regulators
| Hormone | Role in Morphogenesis |
|---|---|
| Auxins (IAA, IBA, NAA) | Controls cell division, elongation and polarity, Establishes apical–basal axis in embryos, Root initiation in cuttings, Vascular differentiation, Maintains apical dominance |
| Cytokinins (Zeatin, BA) | Promotes cell division and shoot morphogenesis, Stimulates shoot bud formation in tissue culture, Enhances differentiation of vascular tissues, Delays senescence (biological process of gradual deterioration with age) |
| Gibberellins (GA₁, GA₃, GA₄) | Promotes cell elongation and organ development, Stem elongation, Flower initiation in LD (long day) plants, Breaks seed and bud dormancy |
| Ethylene (Growth Inhibitor) | Regulates organ abscission and stress morphogenesis, Induces Senescence & abscission (natural process where plants shed parts like leaves, flowers, or fruits at a specialized separation layer), Triple response in seedlings (short, thick, curved), Modifies root hair formation |
| Abscisic Acid (ABA) (Growth Inhibitor) | Growth inhibition and morphogenetic suppression, Maintains seed dormancy, Inhibits shoot growth under stress, Regulates embryo maturation |
Highly recommended to draw diagrams in answers
✅ QUICK REVISION (Exam Snapshot)
- Growth: Quantitative, irreversible
- Development: Growth + differentiation
- Parameters: AGR, RGR, NAR, LAI
- Dynamics: Sigmoid curve
- Morphogenesis: Form & structure development
- Controlled by: Genes + hormones + environment
📚 Sources
- Leopold & Kriedemann (1985)
- Salisbury & Ross (1992)
- Fosket (1994)
- Roberts et al. (2002)
- Salisbury & Ross (1992)
- Leopold & Kriedemann (1985)
- Buchanan et al. (2002)