Vegetative Reproduction and Sexual Reproduction
VEGETATIVE REPRODUCTION or ASEXUAL REPRODUCTION
- Describes reproduction in plants in which new individuals develop asexually from specialized structures such as bulbs, rhizomes, or runners rather than from specialized sex cells.
- Asexual propagation is the production of new plants from the leaves, stems, or roots of a single parent plant. Asexual propagation, which does not require pollination or fertilization, is a rapid method of propagation. It ensures that all of the parent’s genetic material survives even if the parent dies, and it creates offspring, known as clones, with the same traits as the parent plant. Asexual propagation is advantageous when plants are well adapted to a particular environment.
- g. by coppice or root suckers, etc.
- This is the primitive method of reproduction by which a new organism is formed from just one parent without the participation of mate, gamete or fertilization. The offsprings produced by this method are the exact copies and thus identical to their parents and no variations are seen because all the offsprings are genetically identical to their parents. For example: Fission, Budding, Regeneration, Parthenogensis, Cloning.
- In plants, two types of buds are found (i) Dormant buds (originate in the leaf axils and in the bark, each year growing sufficiently to keep the tip just out of wood) (ii) adventitious buds (found in living tissues). When any disturbance occurs in physiological activities e.g. by cutting or by injury, etc these develop shoots.
REASONS FOR VEGETATIVE REPRODUCTION
Vegetative reproduction is adopted under special circumstances, which are as under:
- Inability to produce viable seed (in spp like Banyan, Fig, Oranges, etc)
- True to type spp (exactly similar to mother spp)
- By seed, the seedling may not be like mother tree or somewhat father tree
- In veg reproduction, 100% surety is guaranteed.
- A particular form of plant (e.g. a dwarf tree)
- Modify growth habit (e.g. if Olea ferrugenia, which has good root system but low seed production, is grafted with other Olea spp, which has poor root system but good seed production, the new spp will be modified with not only good root system but also excellent seed production)
- Adaptation of habitat: (by vegetative means the adaptability of a species in a particular area is increased)
- Produce immunity against pests and diseases
- More quantity of plants/ greater no of plants
- Tissue culture
- here a single tissue produces a single plant
- From a single tree, we can produce millions of plants.
- Easy and quick results:
- Sometimes seed collection is a problem e.g. poplar, Tamarix, etc also vegetative means takes lesser times to grow which the seeds take to germinate, establish, etc.
TYPES/ METHODS/ MODES OF VEGETATIVE REPRODUCTION
- When a root of a plant is partially or wholly cut to produce new shoots.
- OR; A shoot arising from the root of the woody plant is called root suckers _ (BCFT)
- Roots of the plant are injured (which results in the disturbance of the physiological functions)
- When new shoots have appeared, the main stem is cut.
- Mainly used for regeneration purposes in Bela Forest in Punjab.
- g. shisham, Populus alba, ailanthus, simal, Robinia, etc.
- When the main plant is cut from near ground, it produces a flush of fresh shoots.
- “A shoot arising from an adventitious bud at the base of the woody plant that has been cut near the ground or otherwise burnt back”_BCFT
- Mainly observed in Eucalyptus, broad leaves, Dodonaea, acacia modesta, Morus alba, Prosopis juliflora, etc. (pic)
- The stem is cut as near to the ground as possible because the adventitious buds are concentrated to collar regions (where adventitious buds are located b/w bark and wood i.e. cambium)
- Factors influencing coppicing:
- Age/ Size of tree
- Greater age less coppicing
- Some trees have coppice power till the age of 50 to 70 years
- Cut the stem before spring i.e. cut in dormant season
- Site characteristics
- Sites having fertile, deep, etc soils produce good coppices.
- Height of cutting
- Cut near collar point
- Coppicing power
- Inherent coppicing power
- Strong coppicers
- Conifers are not at all
- Strong coppicers:
- Fair coppicers
- Acacia nilotica
- Bombax ceiba
- No coppicing
- Pines/ conifers
- Reported in Chir in a young age called seedling coppice
- Age/ Size of tree
- Factors influencing coppicing:
- A portion of stem, root, or branch is planted in the soil. A new shoot is produced.
- Cutting depends upon:
- Age (1-3 yrs)
- Lateral and basal portion give better results than an apical portion or terminal portion
- Season: early spring or late winter
- Deciduous: early spring/ late autumn
- Evergreen: monsoon (because high humidity affects less evapotranspiration)
- Size of cutting (thumb size/ finger size)
- Hormones: (root inducing hormones)
- IAA (Indole Acetic Acid) (make solutions of hormones and dip cuttings and perform the field planting)
- Types of cuttings
- Root Cuttings
- From adventitious buds
- 10 – 25cm length of cutting (3 to 10 inches)
- Placed horizontally underground
- g. shisham, pulonia, Robinia, etc
- Root Shoot cutting
- Cutting having part of the root as well as shoot
- Size is equal to thumb and length 9 inches (6-inch root while 3 shoot)
- The height of stump depends upon moisture availability; greater moisture, longer the shoot
- Also known as stump cutting
- Planting should be as quick as possible
- Stem Cutting/ Branch cutting:
- 10 – 25 cm length of cutting
- One-year-old plant
- Finger size should be the minimum size
- Two-third of the cutting should be in the ground
- The uppercut should be 5 cm above node
- Cutting should be slanted so that moisture could not accumulate
- Cutting should be inserted obliquely
- Cutting should be done before dormant period
- Keep wet while transporting
- Root Cuttings
- In some spp like Philloden spp (ornamental plant)
- Also in Jack pine (pinus bantsions)
- Petiole is removed
- Give superficial cut to the vein
- Place on soil with pins
- It will absorb moisture and will develop roots.
- A method of propagating plants by covering a branch or shoot with soil so that it takes root while still attached to the parent plant
- Methods of Layering:
- Two methods of layering are commonly used.
- Air layering
- Soil Layering
- Remove bark after making a cut
- Place a stone and cover the cut with soil.
- Provide moisture
- Don’t cut the branch from the mother tree in a single cut, rather 1/3 should be cut off the old branch and check its effect on the mother plant. After a week cut it off if there is no effect on the new shoot. If effects are visible, then do not directly cut the branch rather cut it up to ½ lengths.
- E.g. roses, mango, jasmine, grapes, etc.
Soil layering is of following types:
in such layering, a single is branch is inserted in two or three places inside the soil
mainly for that spp having soft and flexible branches, especially for ornamental plants.
Mound layering or Stool layering.
under this condition, cover the plant with soil and new shoots arise
e.g. in apple
This method can be done in an upper atmosphere
- The part of the branch is covered with a polyethene sheet or a plastic cover with soil and tie with spongy material
- Rest of the process is similar as in soil layering ie removal of bark; cutting in intervals, etc. See pic
Image – Twin Graft on an Apple Tree
This picture shows a successful twin graft between two plants. In grafting, the scion, or portion of a plant to be propagated, is physically attached to a seedling or stock plant of the same species using a grafting rubber band and grafting wax. After several weeks, if the graft is successful, the stock and scion will have grown together. Wild plants such as trees and shrubs can also undergo natural grafting, in which their root systems grow together. This allows for the sharing of essential nutrients between different species.
It is the type of reproduction which involves sex cells, the gamates. A male gamete, the sperm, fuses with a female gamete, the ovum, to form a zygote which undergoes development and a new individual is formed. This type of reproduction involves two parents, a male who contributes the sperm and a female who contributes to the ovum.
Flowers contain the structures necessary for sexual reproduction. The male component, or stamen, consists of a thin stalk called the filament, capped by the anther.
Following fig explains the whole process of sexual reproduction in plants
Flower Pollination and Fertilization
Flowers contain the structures necessary for sexual reproduction. The male component, or stamen, consists of a thin stalk called the filament, capped by the anther. The female component, the pistil, includes the stigma, a sticky surface that catches pollen; the ovary, which contains the ovule and embryo sac with its egg; and the style, a tube that connects the stigma and ovary (A). Pollen is produced in the anther (B), and is released when mature (C). Each mature pollen grain contains two sperm cells. In self-pollinating plants, the pollen lands on the stigma of the same flower, but in cross-pollinating plants—the majority of plants—the pollen is carried by wind, water, insects, or small animals to another flower. If the pollen attaches to the stigma of a flower from the same species, the pollen produces a pollen tube, which grows down the neck of the style, transporting the sperm to the ovule (D). Within the embryo sac of the ovule, one sperm cell fertilizes the egg, which develops into a seed. The second sperm cell unites with two cells in the embryo sac called polar nuclei, and this result in the development of the endosperm, the starchy food that feeds the developing seed. The ovary enlarges (E) and becomes a fruit.
- Sexual Reproduction by Seed
- Vegetative Reproduction by Other parts of plants other than seed.
- It consists of two factors a) Flowering b) Seed periodicity
Artificial factors for stimulation of flowering:
- Since flowering is mainly concerned with carbohydrates (C-H-O), therefore, treatments which prevent the movement of carbohydrates from the top also produces early flowering:
These treatments are:
- Root pruning: (injury to roots)
- Girdling: (removing of bark in a circular section)
- Strangulation (to restrict the flow of something) by wire or metal band.
- Inverting of a ring of bark:
- Tying a knot in a young tree/ branch
- Planting at an angle of 45 degrees. (less food transportation)
- Grafting on dwarf root stack
- Training the branches to horizontal position
- Fertilization, esp. phosphorus.
- Sickly trees sometimes produce an abundant crop of small fruit as a last effort before dying.
- Similarly, heavily tapped pines also produce abundant flowers.
- Diseased trees or trees in adverse conditions will produce more flowers to establish their regeneration
- Dominant trees produce more flowers as they receive more light which means more food while a suppress tree does not produce more flowers.
- A single tree produces more flowers because max exposure to sunlight results in more photosynthesis hence more food accumulation.
PERIODICITY OF FLOWERING:
- Periodicity is the regular cycle of flowering/ seeding.
- It is the interval b/w flowering and fruiting.
- The frequency of flowering varies greatly with spp, weather, age and size of trees, and with canopy and crown class.
- Reasons for flowering:
- Genetic characteristics
- Environmental factors
- Soil fertility
- Soil moisture
- Soil nutrients (the yr in which soil has nutrients, tree will produce flowers)
- Examples of spp
- Average cycle for moderate seed year = 6 yrs
- For good seed yr = 10 yrs
- Moderate seed year = 3 yrs
- Good seed year = 4 – 5 yrs
- M s yr = 3
- G s yr = 5 -6
- M s yr = 3
- G s yr = 4 -5
- M s yr = 2
- G s yr = 2 – 3
- M s yr = 1
- G s yr = 1
- M s yr = 1
- G s yr = 1-2
- Majority of the spp are bisexual (both sexes are present)
- Conifers, etc are monosexual (separate sexes)
- Reasons for flowering:
Bamboos produce flowers once in life usually after 40 years but if rhizomes replanted they may produce flowers after 10 years and this is called classical periodicity.
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