Plant Propagation: Merits and Demerits of Sexual and Asexual Propagation & Stock–Scion Relationship

B. Sc. Agriculture (Hons.) Ist. Semester (Six Deam Commitee of ICAR)

Plant Propagation: Merits and Demerits of Sexual and Asexual Propagation & Stock–Scion Relationship

Introduction

Plant propagation is the process of multiplying plants and ensuring the perpetuation of desired species or varieties.
It can be achieved by sexual means (by seeds) or asexual means (vegetative methods).
Each method has its own advantages and disadvantages, and their choice depends on the crop species, propagation purpose, and available resources.

Sexual Propagation

Definition; Sexual propagation is the process of producing new plants by seeds, which are formed through fertilization (fusion of male and female gametes). It results in the formation of genetically variable progeny.

Merits (Advantages) of Sexual Propagation

S.No.	Merit	Explanation / Example
1	Economical and simple	Seed propagation is cheap and easy; ideal for large-scale production of annual crops.
2	Stronger root system	Seed-propagated plants develop tap roots that penetrate deep into the soil (e.g., Mango, Guava).
3	Longer life span	Plants are usually long-lived compared to vegetatively propagated ones.
4	Variation for breeding	Sexual reproduction introduces genetic variation useful for crop improvement.
5	Suitable for rootstock production	Many rootstocks in grafting (e.g., Citrus, Mango) are raised from seeds.
6	Easier storage and transport	Seeds are compact, light, and easy to handle and store.
7	Less disease transmission	Pathogens are rarely transmitted through true seeds.

Demerits (Disadvantages) of Sexual Propagation

S.No.	Demerit	Explanation / Example
1	Genetic variability	Offspring are not true-to-type; each plant differs genetically from parent.
2	Long juvenile period	Fruit-bearing starts late (e.g., Mango may take 8–10 years).
3	Seed sterility or dormancy	Some plants produce sterile or dormant seeds (e.g., Banana, Citrus).
4	Not suitable for seedless varieties	Crops like Banana, Pineapple, and Grapes cannot be propagated by seeds.
5	Heterogeneous crop stand	Plants differ in growth, yield, and fruit quality.

Asexual (Vegetative) Propagation

Definition; Asexual or vegetative propagation is the process of producing new plants from vegetative organs (stem, root, leaf, or tissue) of a parent plant without sexual fusion. The plants produced are clones (genetically identical to the parent).

Merits (Advantages) of Asexual Propagation

S.No.	Merit	Explanation / Example
1	True-to-type plants	Offspring are genetically identical to parent (e.g., Mango, Rose).
2	Early bearing	Plants reach maturity and bear fruits earlier (e.g., Grafted mango bears in 3–4 years).
3	Seedless varieties can be multiplied	e.g., Banana, Pineapple, Grapes.
4	Uniformity	Uniform size, growth, and yield in orchards.
5	Combining desirable traits	Grafting combines good root system with superior scion.
6	Disease-free plants (through tissue culture)	Micropropagation helps produce virus-free plants.
7	Useful in plants with long dormancy or poor seed viability	e.g., Litchi, Guava.
8	Faster multiplication rate (in micropropagation)	Thousands of clones can be produced quickly in labs.

Demerits (Disadvantages) of Asexual Propagation

S.No.	Demerit	Explanation / Example
1	No genetic variation	All offspring are clones; limits natural evolution or improvement.
2	Transmission of diseases	Viral and systemic diseases can spread through vegetative material (e.g., Citrus tristeza virus).
3	Shorter life span	Clonal plants generally live shorter than seed-propagated plants.
4	Costly and labor-intensive	Requires skilled labor and nursery facilities.
5	Not suitable for all crops	Some field crops (e.g., Wheat, Rice) cannot be propagated vegetatively.
6	Bulky planting material	Transportation and storage are difficult compared to seeds.

Comparative Summary of Sexual and Asexual Propagation

Feature	Sexual Propagation	Asexual Propagation
Basis	By seeds (fertilization)	By vegetative organs (no fertilization)
Genetic makeup	Variable (heterogeneous)	Identical (clone)
Uniformity	Not uniform	Uniform
Juvenile period	Long	Short
Life span	Long	Comparatively short
Propagation rate	Slow to moderate	Fast (esp. tissue culture)
Disease transmission	Rare	Common
Examples	Wheat, Papaya, Guava (rootstock)	Banana, Rose, Mango (grafted)

Stock–Scion Relationship

Definition

The stock–scion relationship refers to the physiological and anatomical compatibility and the interaction between the rootstock (lower part) and the scion (upper shoot) in a grafted or budded plant.
The success of grafting and budding depends largely on the compatibility and harmonious growth of these two components.

Parts of a Grafted Plant

Rootstock (Stock):

- The lower portion of the graft.
- Provides root system, anchorage, and nutrient absorption.
- Determines plant vigor, adaptability, and resistance to soil-borne diseases.

Scion:

- The upper portion used for shoot growth.
- Carries desired variety with superior yield or fruit quality.

Factors Influencing Stock–Scion Relationship

Factor	Effect
Genetic compatibility	Graft success is high when both belong to same species (e.g., Mango on Mango).
Anatomical contact	Proper alignment of cambial layers ensures vascular connection.
Physiological activity	Both stock and scion should be in active growth phase.
Hormonal balance	Auxins and cytokinins regulate union and subsequent growth.
Environmental conditions	Temperature (25–30°C) and humidity (80–90%) favor graft union.

Role of Stock in Grafted Plant

Function	Explanation / Example
Anchorage and support	Provides root anchorage and physical stability.
Nutrient and water absorption	Rootstock determines efficiency of uptake.
Influences vigor	Dwarfing or vigorous growth depending on stock (e.g., Apple on M9 rootstock gives dwarf trees).
Resistance to soil problems	Rootstock imparts resistance to drought, salinity, or nematodes.
Influences fruit quality and yield	Rootstock can affect fruit size, maturity, and sweetness.
Longevity of plant	Some rootstocks improve lifespan of scion variety.

Role of Scion in Grafted Plant

Function	Explanation
Determines fruit variety	Scion defines the type, size, and quality of fruit.
Maintains genetic identity	Scion carries the desirable traits of the cultivar.
Controls flowering and fruiting behavior	Regulates reproductive growth and yield characteristics.

Examples of Stock–Scion Combinations

Crop	Rootstock (Stock)	Scion (Variety)	Purpose / Effect
Mango	Local Mango seedling	Alphonso, Dashehari	Vigorous, uniform orchard trees
Citrus	Rough lemon, Trifoliate orange	Sweet orange, Mandarin	Disease resistance and salt tolerance
Guava	Psidium cattleianum	Allahabad Safeda	Wilt resistance
Grape	Dogridge, St. George	Thompson Seedless	Tolerance to drought and nematodes
Apple	M9, M27	Golden Delicious	Dwarfing and early bearing
Rose	Wild Rosa species	Hybrid Tea Rose	Adaptation to soil and climate

Stock–Scion Compatibility and Incompatibility

Compatible union: Both stock and scion grow together harmoniously; e.g., Mango on Mango, Citrus on Citrus.
Incompatible union: Poor vascular connection or rejection occurs; e.g., Peach on Apple, Guava on Mango.

Symptoms of incompatibility:

Weak graft union
Poor growth
Yellowing or wilting
Breakage at graft junction

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