Mastering Plant Propagation: Cloning & Grafting Techniques

Benefits of Plant Cloning

Plant cloning offers several significant advantages for growers:

• Fixed Genotype & Uniformity: Cloned plants retain their exact genetic characteristics, ensuring uniformity in size, growth rate, flowering time, and harvesting time.
• Shortened Time to Flower/Fruit: Clones often mature faster than seed-grown plants.
• Improved Vigor: Plants propagated from cuttings are frequently fuller and stockier.

Methods of Producing Plant Clones

The primary method involves vegetative propagation directly from a mother plant.

Plant Clone Mutation

Mutations in plant clones can be spontaneous (e.g., bud sports) or induced, such as through radiation (gamma rays), as seen in some poinsettia varieties. Mutations that result in dwarfing, variegation, or attractive coloring can be successfully carried through by vegetative propagation, maintaining these desirable traits.

Understanding Clone Variation

Clone variation refers to the presence of an "island" of mutant cells within a stem's growing point. This means that cells of different genotypes can coexist within the plant's meristematic tissue.

Plant Breeders' Rights (PBRs)

Plant Breeders' Rights (PBRs) protect new plant varieties that are New, Distinct, Uniform, and Stable. PBRs are granted for a period of up to 25 years for trees or vines and 20 years for all other plant types. To maintain these rights, the breeder must pay initial application fees and annual maintenance fees for each protected plant clone.

Plant Grafting Techniques

Formation of a Graft Union

Grafting involves joining two plant parts, a scion and a rootstock, to grow as one. The process begins by cutting the scion and rootstock to the appropriate size and shape. Their cambium layers (the thin layer of tissue between the bark and wood) must be precisely aligned to ensure maximum contact. The two pieces are then securely bound together using grafting tape or other suitable materials. A special grafting wax may be applied to seal the graft union, preventing water loss and promoting callus formation, which is essential for successful union.

Types of Scions in Grafting

• Multi-bud Scion: This type contains multiple dormant buds along a single stem, differing from traditional scions that typically have one or two buds. The advantage of a multi-bud scion is its potential to produce multiple shoots or branches from a single graft, thereby increasing the overall productivity of the grafted plant.
• Single-bud Scion: As the name suggests, only one bud will develop into a shoot or branch once grafted.

Budding Techniques

Bud Stick Preparation

Bud sticks are crucial for budding. They are typically collected in July, with leaves removed, ensuring only current season's growth is used. These sticks are then bundled in paper and stored in a cooler. They are later attached to two-year-old rootstock, which can be planted in field rows or kept as potted rootstock.

T-Budding Method

T-budding involves taking a single bud from one plant and attaching it to another. For this technique to be successful, the rootstock must be actively growing. It is primarily confined to roses, fruit trees, and ornamental plants, and is performed during summer months, typically from mid-July to August, when the bark easily "slips" away from the wood when cut.

Chip Budding Method

Chip budding can be performed from mid-July to September, and also in spring. This method involves sliding a side of wood and inserting the bud, ensuring the bud itself is not covered.

Field Grafting Methods

Field grafting is typically performed from early March to April. For successful field grafting, the scion must be dormant, while the rootstock should just be starting to grow.

Whip and Tongue Grafting

In whip and tongue grafting, both the rootstock (RS) and scion must be dormant. This method is commonly used for deciduous plants with materials approximately 1/4 to 1/2 inch in diameter.

Bench Grafting Methods

Bench grafting is performed when the rootstock is growing in a pot, typically within a greenhouse environment. The optimal timing varies by plant type:

• Japanese Maples: Can be grafted anytime of the year.
• Shade Trees: Best done in early spring.
• Conifers: Grafted when dormant.

Side Veneer Grafting

Side veneer grafting is commonly used for conifers, especially those with compact or dwarf forms, onto potted rootstock.

Side Wedge Grafting

In side wedge grafting, conifer needles are removed, and the graft is fashioned and tied at the bottom into the side of the rootstock.

Stock Plant Care

Stock plants are mother plants specifically maintained to serve as a reliable source for harvesting cuttings for propagation.

Stem Maturity: Juvenile vs. Mature

Stem maturity distinguishes between the chronological age of tissue (e.g., in seedlings) and the physiological age of tissue (the mature stage when plants flower and produce seeds).

Stem Growth Patterns and Orientation

The original growth pattern for some shoots can be retained even after rooting, a phenomenon known as a positional or orientation effect. For example, a plant with a sideways orientation may need to be staked to correct its growth direction.

Ripeness of Stem for Propagation

The "ripeness" of a stem for propagation is determined by factors such as the amount of secondary growth, stem firmness, and its overall development throughout the season. Ultimately, maturity for propagation is based on the tissue's capacity to reproduce successfully.

Rooting Hormones and Cutting Preparation

Auxin is a key plant hormone that initiates root formation in cuttings. While auxin promotes root initiation, it does not significantly contribute to root elongation. During cutting preparation, it's observed that the more root initials formed, the more fibrous the resulting root system. Plants that are naturally easy to root often possess sufficient internal sources of auxin.

Key Factors in Cutting Preparation

• Wounding: Stimulates rooting by promoting the accumulation of carbohydrates and auxin at the wounded site, which also increases the absorption of rooting hormones. However, disadvantages include a potential increase in basal rot and higher labor costs.
• Leaf Area Reduction: Involves removing foliage at the base of the cutting, typically leaving 2-4 leaves and cutting back any larger leaves to reduce transpiration.
• Storage Environment: Proper storage conditions are crucial for maintaining cutting viability before propagation.
• Wound Healing & Root Initiation: Understanding the internal steps of wound healing and the precise location of root initials within the cutting is vital for successful rooting.

Propagation House Environment

Maintaining an optimal environment within a propagation house is critical for successful plant propagation. Key environmental parameters include:

• Cutting Environmental Parameters: Careful management of light intensity, humidity levels, water availability, and temperatures.
• Rooting Media Characteristics: Selection of appropriate rooting media with suitable drainage, aeration, and nutrient holding capacity.
• Misting Systems: Implementation of effective misting systems to maintain high humidity and prevent desiccation of cuttings.
• Growth Regulation & Pest Control: Application of growth regulators as needed and diligent pest and disease management to ensure healthy plant development.