Methods of Plant propagation

Objective of Propagation:

The primary goal of propagation is to produce new individuals that are genetically identical to the mother plant or the original plant. A successful propagation method ensures the transmission of all desirable characteristics from the mother plant to its offspring.

While many field crops, vegetables, and flower crops are propagated through seeds (sexual propagation), fruit crops are generally propagated through vegetative means to ensure true-to-type offspring. This is due to the nature of pollination in fruit crops, which are often cross-pollinated and highly heterozygous, making seed propagation unreliable for producing offspring identical to the mother plant.

Sexual Propagation (Seed Propagation):

Sexual propagation involves the raising of plants from seeds. While this method is less commonly used for fruit crops, it does have several advantages and specific applications.

Advantages of Sexual Propagation:

• Cost-Effective and Simple: Seeds are relatively inexpensive and easy to handle compared to the more complex methods of vegetative propagation.
• Longer Life of Seedlings: Seedlings generally have longer lifespans compared to vegetatively propagated plants, making them more resilient.
• Better Root System: Seedlings typically develop better root systems, providing stronger anchorage for the plant.
• Practical for Certain Plants: It is the only viable method of propagation for certain fruit plants such as papaya, phalsa, and mangosteen, which cannot be propagated vegetatively.
• Hybrid Production: Hybrids are initially raised through seed propagation, allowing the creation of new varieties with desirable traits.
• Rootstocks for Grafting: Seed propagation is used to raise rootstocks, which are essential for budding and grafting in various fruit crops.
• Chance Seedlings: Occasionally, sexual propagation may lead to seedlings that possess superior qualities compared to the mother plant.
• Resistance to Pests and Diseases: Seedling plants tend to be more resistant to pests and diseases than vegetatively propagated plants, offering a natural defense.
• Storage and Transportation: Seeds can be stored for extended periods and transported easily to distant markets.
• Hardiness: Seedlings are generally more hardy and can withstand adverse climatic conditions better than vegetatively propagated plants.
• No Special Technical Skill Required: Raising plants through seeds requires minimal expertise compared to more advanced vegetative techniques.
• Virus-Free Plants: Seed propagation is beneficial in producing virus-free plants, as most viruses are not transmitted through seeds.
• Uniformity in Nucellar Seedlings: In some fruit crops, such as citrus and mango, nucellar seedlings (those produced from non-sexual tissue) can be used to create uniform plants.

1. Polyembryony in Crops: In polyembryonic crops like mango and citrus, seeds produce more than one seedling, offering greater genetic uniformity and desirable characteristics.
2. Parthenogenesis in Mangosteen: Mangosteen fruits develop through parthenogenesis (without fertilization), and seeds from such fruits produce offspring that are similar to the mother plant, making seed propagation the preferred method for this crop.

Disadvantages of Sexual Propagation:

1. Heterozygosity: Seedlings are genetically diverse due to the cross-pollination process, making them not uniform in growth, yield, and fruit quality. The offspring may differ significantly from the mother plant.
2. Management Costs: Seedling plants are usually tall and spreading, making operations such as pruning, harvesting, and plant protection more difficult and costly.
3. Long Juvenile Phase: Seedlings typically have a long juvenile phase before they begin to bear fruit, leading to delays in crop production.
4. Low Germination in Recalcitrant Crops: For recalcitrant seeds (those that lose viability quickly after extraction), the germination rate is often very low, making seed propagation less effective.
5. Inability to Use Rootstock Benefits: Sexual propagation does not allow the selection of rootstocks that provide benefits, such as disease resistance or improved growth characteristics, which can be achieved through vegetative methods like grafting.
6. Viability Issues in Some Crops: In crops like pineapple and banana, which do not produce viable seeds, propagation by seed is not possible.
7. No Exact Reproduction of Superior Traits: Seed propagation cannot perpetuate the exact desirable characteristics of superior selections, which can only be done through vegetative propagation methods (e.g., grafting).

Classification of Seeds on the Basis of Storability:

Seeds are classified based on their ability to be stored, depending on moisture content. This classification is into two groups: Orthodox seeds and Recalcitrant seeds.

1. Orthodox Seeds:

• Characteristics: These seeds can be dried to low moisture levels (5-8% or lower) and still retain their viability. They lose their viability if the moisture content increases.
• Storage: The viability of orthodox seeds can be maintained for long periods by drying them and storing them at low temperatures.
• Examples: Ber, custard apple, date palm, fig, grape, guava, mulberry, papaya, passion fruit, peach, pineapple, plum, phalsa, pomegranate, etc.

2. Recalcitrant Seeds:

• Characteristics: These seeds remain viable at relatively higher moisture levels (8-15% or above) and lose viability if dried below a certain moisture level.
• Storage: They are sensitive to dehydration and cannot be stored for long periods like orthodox seeds.
• Examples: Avocado, Barbados cherry, carambola, breadfruit, jackfruit, litchi, mango, mangosteen, rambutan, citrus, etc.

Vegetative Propagation:

Vegetative propagation involves the asexual reproduction of plants using vegetative parts (such as roots, stems, or leaves). This method is based on the concept of totipotency, the ability of plant cells to regenerate into a complete plant under favorable conditions. This term was coined by Haberlandt in 1902.

Advantages of Vegetative Propagation:

• Plants are genetically identical to the mother plant (true to type).
• Uniform growth, yield, and fruit quality.
• Ideal for plants that suffer from seed dormancy (e.g., temperate fruits).
• Easier maintenance compared to seedling plants.
• Ideal for plants like banana, pineapple, fig, guava, and lemon that produce seedless fruit or no viable seeds.
• Plants from vegetative propagation come into bearing earlier than seedlings.
• Can regulate tree size, fruit quality, and early bearing by using rootstocks.
• Allows the use of rootstocks to exploit desirable abiotic effects on scion cultivars.
• Helps overcome self-incompatibility by using top-working methods with pollenizers.
• Virus detection can be performed using indicator plants through methods like grafting.
• Shortens breeding cycles by grafting scions of new cultivars onto established trees.
• Vegetative propagation is necessary for clones and the use of interstocks.
• Repair of damaged tree parts, like trunks or roots, can only be done via bridge grafting or inarching.

Disadvantages of Vegetative Propagation:

• Involves limited genetic diversity, as the plants are clones of the mother plant.
• Some plants may be more prone to diseases due to uniformity.

i) Apomixis:

Apomixis is asexual reproduction in plants where seeds are produced without fertilization. It can occur in several forms:

1. Recurrent Apomixis: The embryo develops from the diploid cell of the ovule (usually the nucellus) without fertilization, resulting in a genetically identical plant.
2. Non-Recurrent Apomixis: Embryos develop from the haploid egg cell or other haploid cells in the embryo sac, resulting in a haploid embryo.
3. Adventitious Embryony (Nucellar Embryony): Embryos develop outside the embryo sac, typically from the nucellus or integuments. This is common in citrus species.
4. Vegetative Apomixis: Buds or bulbils are produced instead of flowers. These can sprout into new plants while still attached to the parent plant, as seen in species like Allium, Agave, and Dioscorea.

Polyembryony is also considered a type of apomixis, where multiple embryos develop in a single seed. This can occur due to the development of multiple nuclei within the embryo sac or early cleavage of the pro-embryo.

Significance of Apomixis:

• Homozygous lines: Apomixis can produce uniform, genetically identical lines.
• Uniform rootstocks: Apomictic seedlings provide uniform rootstock, useful in orchard management.
• Healthier seedlings: Apomictic plants are usually healthier and uniform.
• Virus-free propagation: Apomixis helps in producing virus-free planting materials.
• Reduction of breeding time: By using apomixis, breeders can obtain plants with the desired traits more quickly and effectively.

ii) Cuttings and Types of Cuttings

Cuttings are a common method of vegetative propagation where a part of the plant (such as a stem, root, or leaf) is used to grow a new plant. Here are the different types of cuttings commonly used in horticulture:

Stem Cuttings:

Stem cuttings are the most widely used and convenient method for plant propagation. These cuttings can be taken from the main shoot or side shoots of a plant. The cutting must have sufficient stored food to support its growth until roots are formed. Cuttings taken from young plants generally root better, but older shoots can be induced to produce new shoots suitable for rooting if properly treated.

There are four primary types of stem cuttings:

Hardwood Cuttings:

• • These cuttings are taken from mature, lignified stems of shrubs or trees during the dormant season.
  • The cutting is typically 10-45 cm long, with a diameter of 0.5-2.5 cm. The base is cut straight below the node, and a slanted cut is made at the top.
  • Examples of plants propagated by hardwood cuttings: Grape, mulberry, plum, fig, olive, and pomegranate.

Semi-hardwood Cuttings:

• • These cuttings are taken from partially matured shoots that are not fully woody but have some hardness.
  • The cutting is usually between 7-15 cm long, with a few leaves removed at the base and 2-4 leaves retained at the top.
  • Rooting hormone treatments (IBA at 1000-3000 ppm) are used to aid rooting.
  • Examples: Mango, guava, lemon, and jackfruit.

Softwood Cuttings:

• • These cuttings are taken from tender, succulent shoots that have not become woody.
  • The cutting is typically 7.5-12.5 cm long, and it is best prepared in spring to early summer.
  • Rooting hormone treatments (IBA at 500-1250 ppm) help initiate root formation.
  • Examples: Juniper, lilac, peach, and pear.

Herbaceous Cuttings:

• • These cuttings are taken from soft, succulent, non-woody stems that are typically from annual or perennial plants.
  • Herbaceous cuttings require high humidity to root successfully and may need to be allowed to dry for a few hours before planting.
  • Treatment with IBA (500-1250 ppm) helps initiate root formation.
  • Examples: Geranium, poinsettia, and dieffenbachia.

Root Cuttings:

Root cuttings are used for propagating species that are difficult to propagate through other means. For this, roots of about 1 cm thick and 10-15 cm long are cut and planted to grow new plants. The best time for preparing root cuttings is late winter or early spring when the roots are well-supplied with stored nutrients.

• The cuttings are inserted vertically in the soil (or sometimes horizontally in certain cases, such as with sweet potato).
• Common plants propagated by root cuttings: Blackberry, raspberry, kiwi fruit, fig, and mulberry.

Leaf Cuttings:

Leaf cuttings are occasionally used for propagating certain species, although this method is more commonly applied to herbaceous plants. Leaf cuttings may also include leaf bud cuttings, where a bud is included with the leaf for propagation. Examples include blackberries and raspberries.

iii) Budding in Plant Propagation

In grafting, the scion is a detached piece of shoot or stem with several buds. In budding, however, the scion consists of only one bud and a small portion of wood. Budding is a specialized form of grafting and is often called bud grafting. This method is commonly used for propagating various plants and has several advantages over traditional grafting.

Advantages of Budding:

• Quick and Efficient: Budding is faster and more efficient than grafting.
• Scarcity of Propagating Material: Ideal when propagating material is scarce.
• Excessive Wound Gum: Budding is useful for plants like stone fruits that release excessive wound gum from injury carried to the xylem or wood portion of the stem during grafting.
• Stronger Union: Budding results in a stronger union compared to grafting, which makes the budded plants more resistant to injury from storms and strong winds.
• Simpler Method: It is easier to perform than grafting and can be done by common people with less technical expertise.

Types of Budding:

Shield or T Budding:

• • Procedure: A vertical cut (2.5 cm) is made on the rootstock at about 0-2.5 cm above the soil level. Then a horizontal crosscut is made to form a “T” shape. The knife is twisted to open the bark flaps, creating space for inserting the scion bud. The shield (a piece of bark with a bud) is cut from the budstick and inserted under the bark flaps of the rootstock.
  • Applications: Commonly used for apple, pear, peach, plum, apricot, cherry, rose, and citrus.

Inverted T Budding:

• • Procedure: In areas with high rainfall, water running down the stem may prevent proper healing of the shield piece. In inverted T budding, the transverse cut is made at the bottom of the vertical cut. The shield piece is inserted from the lower part of the rootstock, moving upward.
  • Applications: Mainly practiced in citrus.

Patch Budding:

• • Procedure: The bark of both the stock and scion must slip easily. A double-bladed knife makes two parallel transverse cuts 2.5-3.5 cm apart through the bark. These cuts are connected by a vertical cut to form a rectangular shape. A similar patch is cut from the budstick and inserted into the prepared rootstock.
  • Applications: Successfully used for thick-barked species like walnut and pecan nut.

I-Budding:

• • Procedure: Two parallel cuts are made on the rootstock using a double-bladed knife. These two cuts are joined by a vertical cut at their centers to form the shape of the letter “I”. The flaps are raised to insert the bud patch beneath them.
  • Applications: Primarily practiced in ber.

Ring Budding:

• • Procedure: A complete ring of bark is removed from the stock, completely girdling it. A similar ring from the budstick containing a bud is removed and inserted onto the rootstock.
  • Applications: Used for ber, peach, and mulberry, especially in stocks with thickness less than 2 cm.

Flute Budding:

• • Procedure: In this method, a patch of bark is removed from the stock so that it completely encircles the stock except for a narrow connection between the upper and lower cuts. A similar patch from the budstick is removed and inserted into the vacant area. The patch is tightly wrapped.
  • Applications: Used for ber, mulberry, and peach. Since the stock has a narrow bark connection, it remains alive even if the bud fails to sprout.

Chip Budding:

• • Procedure: A chip of bark is removed from the rootstock near the base between nodes, and a similar-sized chip from the budstick is replaced. The cuts are made at an angle, with the second cut made above the bud. Both chips are cut in the same manner and swapped, and the bud piece is wrapped properly, leaving the bud uncovered.
  • Applications: Mainly followed in grape, apple, and pear, especially when the bark does not slip easily and the plants are not in an actively growing condition.