Stock, Scion and Inter Stock relationship

Stock, Scion and Interstock – Definitions and Concepts

Stock (Rootstock):

• It is the lower portion of the graft that develops into the root system. It influences growth, resistance, and adaptability.
• Example: Rangpur lime is used as a rootstock for sweet orange due to its drought resistance.

Scion:

• It is the upper part of the graft which is selected for desirable horticultural traits like fruit quality, size, and productivity.
• Example: Alphonso mango scion grafted onto Bappakai rootstock retains Alphonso’s quality with controlled tree size.

Interstock:

• An intermediate segment used between stock and scion. It can address incompatibility, manage tree size or improve graft union.
• Example: In pear, Quince A rootstock is incompatible with some pear varieties, so ‘Old Home’ interstock is used.

Statistical Insight:

• In citrus, Carrizo citrange rootstock occupies over 30% of rootstock use in commercial citrus orchards globally.

2. Stock-Scion Relationship

Effect of Stock on Scion:

• Controls vigour: M9 rootstock reduces apple tree height to 40–60% of standard.
• Impacts yield: Grape rootstock Dogridge increases productivity under saline conditions.
• Improves disease resistance: Jatti Khatti rootstock in citrus offers resistance to certain soil-borne pathogens.

Effect of Scion on Stock:

• Some scions can suppress or enhance rootstock growth.
• Example: Sweet orange scion on Swingle citrumelo rootstock shows better nutrient uptake.

Statistical Insight:

• Studies show that using M9 rootstock in apples can lead to 60–80% increase in yield efficiency (kg fruit per cm² trunk area) compared to seedling rootstocks.

3. Interstock Use and Effects

Functions of Interstock:

• Overcomes graft incompatibility.
• Induces dwarfing and precocity.
• Improves graft survival and union quality.

Example:

• In apple, using M9 as an interstock on a vigorous MM111 rootstock balances tree vigor and ensures compatibility.

Statistical Insight:

• In Japanese apple orchards, over 25% of trees use interstocks to manage tree size and compatibility issues.

4. Graft Incompatibility

Definition:
It is the failure of stock and scion to form a functional, long-lasting union due to physiological or genetic differences.

Causes:

• Anatomical mismatch in cambium.
• Biochemical incompatibility (e.g., phenolic accumulation).
• Genetic distance between stock and scion.

Symptoms:

• Bark cracking or bulging at union.
• Yellowing, stunted growth, early leaf fall.
• Sudden death (e.g., pear on incompatible quince).

Examples:

• Mango cv. Neelum shows incompatibility on some wild mango rootstocks.
• Peach and apricot graft failure due to translocated incompatibility.

Statistical Insight:

• More than 40% of incompatibility in temperate fruit crops is attributed to vascular discontinuity at the graft interface.

5. Physiology of Rootstock

Functions of Rootstock:

• Absorbs water and nutrients.
• Modifies hormone flow (e.g., cytokinin, auxin).
• Affects flowering and fruiting time.
• Provides tolerance to stresses (salt, drought, cold).

Examples:

• Dogridge grape rootstock shows better salt exclusion capacity.
• Ber rootstock Ziziphus nummularia provides drought tolerance in arid regions.

Statistical Insight:

• In grape, yield on Dogridge rootstock in saline soils is 35–50% higher than on own-rooted vines.

6. Top Working

Definition:
Top working involves grafting superior scion varieties on established trees to change their cultivar or rejuvenate old orchards.

Steps:

• Heading back old tree.
• Grafting new scions (cleft or bark grafting).
• Managing sprouts and suckers.

Advantages:

• Quick rejuvenation.
• Multi-varietal trees can be created.
• Faster fruiting than replanting.

Examples:

• In mango, old seedlings are top-worked with Alphonso or Kesar.
• In guava, Allahabad Safeda is top-worked on local seedlings for better yield.

Statistical Insight:

• Top-working in mango improves productivity by 40–60% and shortens the non-bearing period by 2–3 years.

7. Factors Affecting Compatibility

7. Genetic Relationship:

• Compatibility is better within species or closely related genera.
• Example: Mango on Mangifera indica stock is usually compatible.

2. Age and Physiology:

• Stock and scion should be at a similar physiological stage.
• Example: Semi-hardwood scion used on actively growing stock in guava.

3. Cambial Contact:

• Perfect alignment is essential.
• Example: In cleft grafting of ber, cambial match determines success.

4. Season and Environment:

• Best time is when cambial activity is high – spring or rainy season.
• Example: Citrus budding in July-August gives highest success in north India.

Statistical Insight:

• Improper cambial alignment is responsible for over 50% graft failures in commercial fruit nurseries.

8. Recent Research and Applications

Advancements:

• Molecular markers (RAPD, SSR) are being used to predict compatibility.
• Hormonal profiling is done to understand incompatibility responses.
• Use of tissue culture for uniform and disease-free rootstocks.

Examples:

• RAPD analysis used in citrus to select compatible combinations.
• Use of micrografting in mango and citrus in vitro to test compatibility.

Statistical Insight:
Rootstock trials in citrus under ICAR-CCRI have shown Carrizo citrange to be 20% more productive than traditional rough lemon rootstocks in long-term trials.

 Crop-wise Rootstock Example Table

Statistical Insight:

• Carrizo and Swingle rootstocks together account for more than 50% of citrus rootstocks used in Florida, USA.

10. Important Points

• M9 is the most used dwarfing rootstock in apple cultivation worldwide.
• Incompatibility between quince rootstock and pear scion is overcome using ‘Old Home’ interstock.
• Dogridge grape rootstock is highly salt tolerant and increases yield by 35% under saline irrigation.
• Jatti Khatti is the most commonly used citrus rootstock in North India due to its vigour and adaptability.
• Top working is best done in spring (February–March) or monsoon (July–August) depending on region