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Plant propagation is multiplication of plants from their parent plants. In vegetable crops there are two methods of propagation i.e. sexual and asexual propagation. Sexual reproduction involves union of the pollen and egg cell to create a new, third individual having genes from two parents. In sexual propagation flowers are involved in the development of seeds. Seeds can be either directly seeded in the field or transplanted after growing seedlings in nursery beds. Sexual or seed propagation, is common in case of tomato, brinjal, chilli, bean, okra, broccoli, cabbage, carrot, cauliflower, cucumber etc. In asexual or vegetative propagation plants are multiplied by plant parts which regenerate itself into a new plant. The methods of asexual propagation followed in vegetable crops are cuttings, bulbs, tubers, crown division and grafting. Vegetative propagation is common in potato, sweet potato, pointed gourd, taro, ginger, turmeric, artichoke, garlic, rhubarb and asparagus. Each method of propagation has their own advantages and disadvantages. Sexual propagation is easy, cost effective cheaper and quicker than other methods and it may be the only way to obtain new varieties and hybrid vigor in crop species, it is the only viable method for propagation and a way to avoid transmission of certain diseases. The method of asexual propagation is easier and faster method of propagation. In some crops like garlic, turmeric, colocasia and ginger which do not or rarely form any seeds it may be the only way to perpetuate. It bypasses the juvenile characteristics of certain species. The resulting new plants are genetically identical to their parents. Apart from conventional methods of propagation there are some new approaches like micro propagation, tissue culture and aeroponics to produce early and disease free planting material. Vegetable grafting is another important method to produce stress and disease tolerant planting material. These all methods are thoroughly discussed in this chapter with suitable examples.
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Methods of Propagation in Vegetable Crops
Aanchal Chauhan1*, Deepa Sharma2, Rajeev Kumar1, Kumari Shiwani1and Neha Sharma1
1College of Horticulture and Forestry, Dr. Y S Parmar University of Horticulture and Forestry, Thunag, Mandi, Himachal
Pradesh, India 175048
2College of Horticulture and Forestry, Dr. Y S Parmar University of Horticulture and Forestry, Neri, Hamirpur, Himachal
Pradesh, India 177001
* E mail: aanchalchauhanrana@gmail.com
Abstract
Plant propagation is multiplication of plants from their parent plants. In vegetable crops there are two methods of
propagation i.e. sexual and asexual propagation. Sexual reproduction involves union of the pollen and egg cell to
create a new, third individual having genes from two parents. In sexual propagation flowers are involved in the
development of seeds. Seeds can be either directly seeded in the field or transplanted after growing seedlings in
nursery beds. Sexual or seed propagation, is common in case of tomato, brinjal, chilli, bean, okra, broccoli,
cabbage, carrot,cauliflower,cucumber etc. In asexual or vegetative propagation plants are multiplied by plant parts
which regenerate itself into a new plant. The methods of asexual propagation followed in vegetable crops are
cuttings, bulbs, tubers, crown division and grafting. Vegetative propagation is common in potato, sweet potato, pointed
gourd, taro, ginger, turmeric, artichoke, garlic,rhubarb and asparagus. Each method of propagation has their own
advantages and disadvantages. Sexual propagation is easy, cost effective cheaper and quicker than other methods and
it may be the only way to obtain new varieties and hybrid vigor in crop species, it is the only viable method for
propagation and a way to avoid transmission of certain diseases. The method of asexual propagation is easier and
faster method of propagation. In some crops like garlic, turmeric, colocasia and ginger which do not or rarely form
any seeds it may be the only way to perpetuate. It bypasses the juvenile characteristics of certain species. The resulting
new plants are genetically identical to their parents. Apart from conventional methods of propagation there are some
new approaches like micro propagation, tissue culture and aeroponics to produce early and disease free planting
material. Vegetable grafting is another important method to produce stress and disease tolerant planting material.
These all methods are thoroughly discussed in this chapter with suitable examples.
Key words: Grafting, Nursery,Propagation, Seed, Vegetable crops, Vegetative propagation
Introduction
Plant propagation is defined as multiplication or reproduction of plants. Propagation of plant is the
involvement of science and art in a skillful way. With basic knowledge and skill it can be a better source of
income generation through commercial nurseries. We can also maintainin the plant stock and preserve
endangered (extinct) species using this method of propagation. In vegetable crops there are three methods of
plant propagation i.e. sexual propagation (seed propagation), asexual propagation (vegetative propagation) and
micropropagation (tissue culture).Vegetables are generally propagated either by seed or vegetatively using
stem cuttings, tubers, bulbs and corms. When sowing the seeds there are further two methods by which seed
can be sown i.e. direct sowing in the fields or by producing nursery seedlings for transplanting in the field.
Table 1.Various classes of vegetables based on planting material and sowing method (Source: Thamburaj
and Singh, 2000)
Crop
Propagation method
Direct sown crops (seed)
Radish, carrot, peas, beans, cucurbits, turnip, coriander, okra,
sweet corn, spinach
Transplanted crops (seed)
Cabbage, cauliflower, brinjal, tomato, capsicum, chilli, knol
khol, onion
Plantingbulbs and
rhizomes
Onion,garlic, ginger and turmeric
Planting tubers and corms
Potato, yam, taro
Planting vines and cuttings
Pointed gourd, sweet potato and cassava
Divisions of crown/suckers
Asparagus, rubarb and globe artichoke
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Propagation by sexual propagation / seeds:
Propagation or multiplication of plants by means of seeds is known as sexual propagation. Seeds formation is
a result of successful fertilization and combination of parental gametes. It is one of the primitive and easy
method and is widely used for the propagation of crops plants. Good quality seed is the basic requirement for
success in vegetable production. Most of the vegetables are propagated by true seed except potato, sweet
potato, pointed gourd, asparagus, colocasia, yam, cassava, garlic, ginger and turmeric. At present in case of
potato also true potato seed (TPS) is being used commercially.
Merits of seed propagation
Seed propagation leads to vigorous plants with resistance to biotic (insect-pests and diseases) and
abiotic stresses (environmental conditions) with long life.
It is an simple, convenient and easy method. Some plants like papaya, marigold, chilli, capsicum,
tomato, etc., cannot be propagated by sexual method.
It is the way of creating genetic diversity of plants.
Few varieties and cultivars of vegetable crops like hybrids can be developed only by this method.
Basic material for budding and grafting can be raised by this method only.
It is easy to store seeds in small space for longer time using this method.
Demerits of seed propagation
Due to segregation sexually propagated plants show variations and are not genetically true-to-type to
the other plants.
Plants propagated through seeds have long gestation period, which leads to delayed flowering and
fruiting.
Seed grown plants are vigorous and it makes intercultural practices like harvesting weeding, spraying
etc. a tedious task.
Advantages offered by rootstocks and scion as in asexual propagation cannot be exploited through
sexual method.
Crop species, which do not produce seeds, cannot be multiplied by this method.
Seed can be defined as a ripened ovule and it consists of three parts i.e. embryo, stored food material in the
form of endosperm and seed coat. For successful crop production good quality seed is of utmost importance.
Although it cost a small portion of the total cost of crop production, quality of seed strongly affects crop yield.
Seed of good quality are accurately labelled, clean, graded to size, viable, and free of diseases and insects. The
seed should be obtained from reliable source. Seed viability which is ability to grow, and longevity, the period
of viability, are very important characteristics of seeds. The dry seeds of all vegetables should be packed in
hermetically sealed cans under vacuum.
Table 2. Viability of vegetable seeds stored under favorable conditions.
(Source: Arya, 2006)
Crops
Seed viability
(Years)
Lettuce
6
Radish, Collards, Cucumber, Endive, Muskmelon
5
Beet, Squash, Cauliflower, Fennel, Kale, Eggplant, Swiss Chard, Chicory,
pumpkin, Rutabaga, Mustard, Brussels sprouts, Cabbage, tomato, turnip,
Watermelon
4
Bean, Asparagus, Broccoli, Carrot, Kohlrabi, New Zealand spinach, Celeriac, Pea,
Spinach, Chinese cabbage, celery
3
Leek, Okra, Pepper, Sweet corn
2
Onion, Parsley, Parsnip, Salsify
1
In vegetables trend of hybrid production is increasing now a days. Hybrid results in high quality produce with
uniform shape and colour. A number of F1hybrids are available in tomato, cabbage, brinjal, chillies and
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cucurbits but none had yet been introduced for the bean, celery, lettuce, parsley etc. Soil moisture, temperature
and oxygen as well as light conditions are important factors to be considered. Most of vegetable seed
germinates at about 60oto70oF (16-21oC). There must be enough moisture, soil should not be wet which
means the soil must be moist to about 50 to75 per cent of soil moisture holding capacity. Many vegetable
seeds of cool weather season crops can germinate in the soil as cool as 45oto50oF (7-10oC). Different
vegetables have different requirement of soil temperature for desired seed germination. Some vegetables like
bean, cucumber, eggplant, lima bean, muskmelon, okra, pepper, pumpkin, squash, and watermelon do not
germinate at a temperature below 60° F (16° C). At extremely high temperature (>32° C) vegetables crops
such as celery, lettuce, lima bean, parsley, pea, and spinach will not germinate as they require low temperature
for germination. Some of the vegetable seeds have special requirements to germinate. For example Lettuce
and Savory seeds require light treatment to germinate. Some crops like broccoli, Brussels sprouts, cabbage,
cauliflower, Chinese cabbage, collard, cucumber, eggplants, kale, chillies, tomato, melons etc require little
soil cover to germinate and should be lightly covered. Vegetable seeds must be planted to a depth that is three
times the thickness of the seed. All the seed should be planted in humus rich loamy soil that is rich in organic
matter. Seed should be treated with fungicides prior to sowing to avoid soil born diseases.
Method of planting
Vegetables seed can be directly seeded in the field or it can be transplanted after raising nursery. Directly
seeded plants are economical as compared to transplants, as they can grow continuously without the check in
growth often seen by transplanting (Orzolek, 1984). Seed propagation is an important method for agronomic,
forestry, vegetable, and flowering bedding plants. In vegetables direct field seeding is a common propagation
method for okra, peas, beans, radish, carrot, turnip, corn, coriander, and spinach. The crops whose seed is very
costly and which can wear transplanting shock are usually first planted in the nursery beds and then
transplanted to the main fields. While selecting the site for vegetable production it should be flat with good
soil water drainage. A good seed bed should have a loose but fine physical texture that produces close contact
between seed and soil so that moisture can be supplied continuously to the seed. Such a soil should provide
good aeration, but not too much or it dries too rapidly. The surface soil should be free of clods and of a texture
that will not form a crust. Soil impedance due to crusting from an improperly prepared seed bed or adverse
environmental conditions during seeding can substantially. Some benefits of direct sowing are:
Direct sowing requires lesser work than transplanting.
Specialized structures like greenhouse and other equipments are not required.
Direct sown plants are more tolerant to drought tolerance and their roots grow without damage.
Some crops like melons, carrot and radish are not amenable to transplanting because they have delicate
stems and roots get distorted if transplanted.
Some crops like carrot have millions of plants and it becomes difficult to transplant them.
There are some vegetables such as tomato, egg plant, rayo, cabbage and cauliflower cannot grow directly by
sowing the seed in the field. Their seedling are first raised in the nursery beds and then transplanted in the
main fields. Transplanting of seedling also eliminate the need of thinning and virus free vigorous off season
nursery can be raised in protected condition. It is convenient to manage seedling under small area by taking
timely plant protection measures are with minimal efforts. Seed cost of some crops like hybrid vegetables is
usually very high, as a single seed is valuable they need to grow under protected conditions. Nursery raising
not only reduces the crop span but also leads to uniform crop and thus, harvesting as compared to direct sown
crops. Some benefits of transplanting seedling are:
It is possible to grow a large number of plants per unit area.
Small and expensive hybrid seeds can be raised more effectively due to better care and management.
It increases the germination percentage of seeds and the seedlings vigour.
Seedlings can be managed in a better way with minimum care and inputs.
Manipulation of growing conditions for plants becomes easy.
By selecting vigorous and healthy seedlings we can get uniform crop growth in the main field.
Off-season seed sowing becomes possible by growing nursery in polyhouses.
The seed requirement of nursery raised crops is lesser as compared to direct seed sown crops which
ultimately save the cost of costly hybrids.
Sowing seeds in a nursery allows additional time for doing preparatory tillage in the main plot. Harvesting
of the previous crop can also be prolonged, if needed.
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It is easy to control insect-pests, diseases and weeds easily in the nursery.
Preparation of nursery
Selection of site
While selecting the site care should be taken that the nursery area is nearer to the water source and site is
partially shaded i.e. under the trees. If not, artificial shade is to be provided. It should be well protected from
animals and proper drainage facilities should be provided. Soil with medium texture, loamy or sandy loam soil
which is rich in organic matter should be preferred. Several vegetable species, including tomato, pepper,
cabbage, broccoli, and onion, can be produced from transplants produced in field nurseries. This is an
alternative to direct seeding and is less expensive than container-grown transplants produced in greenhouses.
Warm-season crops are usually seeded in spring and may be covered with plastic or fabric (floating) row
covers to prevent frost injury. Cool-season crops are seeded in early spring or summer for a fall harvest. For
many species (especially woody and herbaceous native plants), seeds must be treated to overcome seed
dormancy conditions. Practice of soil solarization i.e. covering the moist soil air tight from all the sides for
about 4-5 weeks with the plastic sheet to prevent soil born diseases.
Nursery bed preparation
Nursery beds should be prepared according to the crop and seasons. In rainy season raised beds are preferred
whereas flat beds are suitable for the winter and summer seasons. For nursery bed preparation soil, sand and
well rotten FYM should be mixed in the ratio of 1:1:1.
There are three methods of nursery bed preparation:
Sunken bed: The soil of the seedbed needs to be sterilised by soil solarisation or with chemicals to avoid
contamination by pests and diseases. The soil of the nursery bed is thoroughly mixed with rotten farmyard
manure. This type of nursery bed is prepared in dry and windy areas. In dry areas, the bed is kept 10−15 cm
below the ground level, which helps in conserving water. Sunken bed facilitates the deposition of irrigation
water or rainwater for a longer time. In case of water scarcity, this type of bed helps to conserve the moisture.
Such a bed can be easily irrigated during dry season. A sunken bed provides protection to the seedlings during
high wind conditions as they are covered.
Flat or Level bed : These type of beds are flat, 1-metre wide and has length according to the slope of the field.
Irrigation channels are prepared between the rows of the beds through which each bed is connected. These
also act as drainage channels in case of heavy rain or excess irrigation. Such a bed is prepared during non-
rainy season (summer and winter) so that there is no water logging. Adequate drainage provision is made and
preference for sandy or sandy loam soil is given when preparing a flat bed.
Figure 1. Different types of nursery beds
Raised bed: Such a nursery bed is prepared during the rainy season. This type of bed is prepared about 15 cm
high from the ground level. The width is kept at 1−1.5 m and length 3−5 m. This enables adequate drainage
during rains and checks water stagnation. A space of 30−40 cm is left between two beds in order to carry out
cultural practices smoothly.
Sowing of seeds in the nursery
After the seed bed is prepared then the seed are sown in the nursery bed in the different way. Seeds are either
broadcasted in the well prepared nursery beds or sown in lines. The sowing time and seed rate varies from
crop to crop. Seed rate for some commercial vegetables is given in table 2.
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Table 3: Seed rate of different vegetables. (Source: Arya, 2006)
Vegetables
Seed rate (g/ha)
Nursery area required
(Cm2/ha)
Tomato(hybrid)
200-250
75-100
Tomato (OP)
400-500
100-125
Brinjal
400-500
75-100
Chillies
500-600
75-100
Capsicum
400-600
100-150
Early cauliflower
700-750
100-150
Mid and late cauliflower
400-500
100-150
Cabbage
450-500
75-100
Kohlrabi
700-750
100-150
Onion
8000-10000
500
After seed sowing seeds they are covered with the fine mixture of soil, sand and FYM in the ratio of 1:1:1.
After covering a light irrigation must be given with the fine rose can and nursery beds should be mulched with
a thin layer of paddy straw mulch or grass or any organic mulch during hot weather and by plastic mulch in
cool weather. Mulching helps to maintain the proper soil moisture for seed germination. Soon after seeds start
germination to mulch should be removed carefully remove to avoid damage to the emerging seedlings.
Nursery bed should be lightly irrigated with the help of rose can till seed get germinated. Excess irrigation
should be avoided and water must be applied as per the need. Proper thinning and weeding should be done to
get healthy disease free seedlings. Vegetables seeds starts to germinate from three days to two weeks after
seed sowing depending upon the species. Days taken to germination by different vegetables are mentioned in
table 3. Before transplanting the seedlings they are first hardened by gradually restricting the water supply and
exposing them to sunlight. This is done to avoid stress or transplanting shock to the seedlings at the time of
transplanting to the main field. Hardening can be accomplished by exposing the plants to increased light
intensity, reducing water supply and fertilizer application.
Table 4. Day taken by different vegetable crops to germinate (Source: Arya, 2006)
Hi-tech vegetable nursery production
Seed cost of hybrids in vegetable crops like tomato, brinjal, capsicum and cucurbits is very high and therefore
it becomes necessary to grow nursery under protected conditions to get higher germination and disease free
healthy seedlings. To raise seedlings in protected environment seed sowing is done in soilless media in plug
trays. Soil-less media consists of coco-peat and vermiculite and one seed is manually placed in each cell of the
seedling tray and covered with media. However, this method is labour-intensive, time consuming and required
more labour for cultural operation. Mechanized precision seed sowing in seedlings trays can prove effective to
enhance the capacity of rapidly growing nursery industry in India.
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Figure 2. Seedlings raised in plug trays
Asexual propagation
Another method of propagation in vegetable crops is asexual propagationor vegetative propagation in which
vegetative parts of a plant like leaf, stem, root, tubers or their modified forms are used for regeneration of new
plants.
Merits
Crop plants which are not able to produce seeds are easily multiplied by this method.
Plants propagated by asexual propagation are true-to-type i.e. they are exactly similar to their parent plant.
By top working (using budding and grafting), old and economically low productive crop plants can be
developed into superior ones.
Advantages offered by rootstocks and scion can be exploited through asexual method.
Vegetatively propagated plants are uniform in maturity and the plant gives quality yield.
Plants propagated by asexual method are generally small sized making cultural operations like spraying
of chemicals and harvesting etc. easy.
Demerits
It limits the development of new varieties as in case of sexual propagation.
Specialised skills are required for cutting, grafting etc. so it is an expensive method of propagation.
Asexually propagated plants have sghort life span as compared to sexually propagated ones.
Vegetatively propagated plants are more prone to biotic and abiotic stresses.
Methods of asexual propagation in vegetables crops are:
Cuttings
Vegetables like pointed gourd, sweet potato and tapioca are commercially propagated by means of cuttings. A
cutting is a vegetative plant part which is taken from the parent plant and it regenerate itself to form a whole
new plant. Pointed gourd botanically known as Trichosanthes dioica Roxb. and belongs to family
cucurbitaceae is usually propagated through vine cuttings and root suckers. Due to of poor seed germination
and inability to determine the sex of plants because seed may contain 50% non fruiting male plants before
flowering vegetative propagation is preffered in this crop. Vine cuttings having 8–10 nodes per cutting are
made in the fall of previous year and rooted during winters. Cuttings should be partially or fully defoliated to
check transpiration. The vines should be planted at a distance of 1.5–2.0 m × 1.5–2.0 m depending on the
method of training of vines (Singh 1989; Yadav 1989). Optimum ratio of female:male is 9:1 for maximum
fruit set (Maurya et al. 1985).
Other important vegetable crop propagated by vine cutting is sweet potato which is botanically known as
Ipomoea batatas and belongs to family convolvulaceae. Its plants can be propagated by seed, storage roots or
from vine cutting. Stem cuttings from the vines develop root and form new storage roots. In some colder
climates, where vines do not develop well, producers will plant roots. Botanical seed is also used in breeding
programs.Vine grow rapidly horizontally on the ground, and planting material can be easily and quickly
multiplied from very few roots. Cuttings of 20 to 40 cm long and having three to five growth buds should be
taken from the tips of young stems. These cutting are first planted in primary nursery beds at 60 × 20 cm
distance. After 45 days the vines are cut to a length of 20-30 cm and again planted in secondary nursery beds
at 20 cm distance. The planting material is then wilted for few days to encourage root initiation and then
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transplanted into the main field at 60 × 20 cm distance. If cuttings are not available, tubers can also be used
for propagation.
(a) (b) (c)
Figure 3. Vine cuttings of a) Sweet potato, b) Pointed gourd and c) Cassava
The use of cuttings has been evaluated for the rapid clonal propagation of potato Nodal cuttings provide a
method of potato propagation which is both simpler and more rapid than current aseptic culture techniques
(Cole et al.1967; Goodwin, 1981)
Cassava is also propagated by stem cuttings. Stems are cut from matured plants after harvest. Cassava is
propagated by cuttings, by planting pieces of stem. Cuttings should be taken from 2 to 4 cm thick stem of the
strongest, disease free plants which have already produced tubers. After the harvest, selected stems are tied in
bundles and kept for at least 10 days before planting in a cool, dry place. Cut each stem into pieces 20 to 30
cm long. There should be 4 to 6 growth buds on each piece. Each stem can be made into 4 or 5 cuttings.
Cuttings are planted on mounds or ridges 1 to 1.5 meters apart from row to row, and 1 meter apart from plant
to plants. With this spacing 7 000 and 10 000 cassava plants can be accommodated in one hectare area (Osei
et al. 2009).
Stem Tubers:A stem tuber is growth that forms from thickened rhizomes or stolons. The top sides of the
tuber produce shoots that grow into typical stems and leaves and the bottom of the tuber produces roots.
Ordinarily stem tubers form on the sides of the parent plant, usually near the soil surface. Potatoes is mostly
cultivated by planting stem tubers. Purity of the cultivars and healthy seed tubers are the primary requirements
for a successful crop. However, seed tuber is the costliest input in potato cultivation. The tuber seed should be
disease free, well-sprouted and 30-40 g each in weight. It is advisable to use the entire seed tuber for planting.
Hill tuber seeds are split into pieces and planted late in winter when they do not decay due to mild
temperatures. The main objectives of cutting large size tubers are to reduce the cost of seed and to obtain
uniform sprouting. Tubers should be cut longitudinally through the crown eye and the weight of the cut piece
should be around 30-40 g. Usually the seed tubers are cut with a knife just and treated with a fungicide before
planting. Before cutting the seed tuber, the knife should be disinfected with Potassium Permanganate solution.
The shortage of good quality seed tubers, high seed cost, transportation of bulky potato seed, and virus
infiltration in seed tubers are some of the important problems associated with use of seed tubers as planting
material. In-vitro multiplication of virus-free microplants and microtuber followed by minituber production in
net house and aeroponic techniques is most important components of high-tech seed production which
overcomes drawbacks of conventional seed production system (Murlidhar et al. 2017; Bag et al.2015).
Figure 4. Mini seed tuber production using aeroponics in potato
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Bulbs: A bulb is a round, swollen part of a stem, basically a short stem with leaves, that serves as food storage
during dormancy. Bulbs consist of a bud that is surrounded by layers of fleshy, scale-like leaves. These leaves
are the source of food storage and provide nourishment for the new plant. Onion and garlic are propagated
through bulbs. Onion can be propagated by small sized bulbs(1.5-2.0cm ) known as sets whereas garlic being
a self sterile crop is entirely a vegetatively propagated crop.Most garlic varieties do not produce fertile seed so
the plant is propagated from the cloves. Individual cloves are obtained by breaking apart the bulb. Cloves of 8-
10 mm diameter size give increased yield of better quality, care should be taken to select bigger cloves from
outer side of bulbs. About 500 kg cloves of 8-10 mm diameter are required to plant one hectare. Cloves should
be planted 5–8 cm (2-3 in) deep, leaving 8–10 cm between individual plants and 15–20 cm between rows. The
cloves should be planted pointed side up with the basal plate positioned downwards. Garlic is affected by a
viral mixture and production of virus-free garlic plants has been attained through shoot tip culture
(PenaIglesias and Ayuso, 1982), meristem tip culture (Li et al, 1995) and by thermotherapy in combination
with meristem tip culture (Senula et al, 2000). Corms:A corm is a short, vertical, swollen underground plant
stem that serves as a storage organ used by some plants to survive winter or other adverse conditions. It is
distinguished from a bulb in that it does not grow in layers. A corm is the base for the flower stem and has a
solid texture. A large new corm forms on top of the old corm, and tiny cormels form around the large corm.
After the leaves wither, dig up the corms and allow them to dry in indirect light for 2 or 3 weeks. Remove the
cormels, and then gently separate the new corm from the old corm. Dust all new corms with a fungicide and
store in a cool place until planting time. Taro or colocasia and yams are propagated using cormels weighing
20-25g. Either young suckers or mature setts cut from harvested corms are used for planting taro. Planting
material must be taken from healthy plants. Cormels are planted at a depth of 5–7.5 cm. Planting on ridges
facilitates harvesting. The planting distance is 20–30 cm between the plants and 30-45 cm between the rows is
kept. For breeding purposes taro can be propagated by seed. In case of yams the corm is cut into 750-1000g
small bits in such a way that each bit has atleast a small portion of the ring around each bud. Whole corms of
500 g size can also be used as a planting material. Use of cormels and minisett transplants of 100 g size as
planting material at a closer spacing of 45 x 30 cm is also suggested.The pieces are planted in such a way that
the sprouting region (the ring) is kept above the soil. About 3500 kg of corms will be required to plant one
hectare. The cut pieces are planted in beds at 45 cm x 90 cm spacing. Sprouting takes place in about a month.
Figure 5. Corm of Taro and Elephant Foot Yam
Rhizomes: A rhizome is essentially a thick horizontal continuously-growing extension of a plant that grows
under or along the ground and that can develop new roots and shoots.eg. ginger and turmeric. Ginger
(Zingiber officinale) and turmeric (Curcuma longa) are from the Zingiberaceae family, and are ancient crops
domesticated centuries ago. Turmeric and ginger is most commonly and easily propagated by dividing the
fleshy root rhizomes and planting these segments. Seed rate varies between 1.0 to 3.0 t ha-1 . Seed size
also varyfrom mini-sett or micro rhizome of less than 5 g to150 g. But an ideal size would be 25 to 50g.
The rhizomes should be planted 5-7 cm deep. It is often planted on ridges, usually about 30-45 cm apart and
with 15-30 cm between plants. Rhizomes are seed material have to be stored during off-season for about 90
to 120 days betweenharvest and subsequent planting. Seed storage is veryessential to maintain good seed
health. The seedrhizomes should be stored appropriately so that rotting; shriveling, dehydration
and sprouting areavoided until the next season. Storage losses can often be as high as 10-50 per cent (Prasath
et al. 2017). Recovery of seed rhizomes at planting was as high as 96 per cent by selecting fully matured
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rhizomes for storage, dipping in asolution of quinalphos 0.05% and Dithane M45 0.3% for 30 min and
drying under shade and storing in pits (wherever bacterial wilt is a problem in ginger, the seeds should be
treated with streptocycline 200 ppm).
Figure 6. Rhizomes of Ginger and Turmeric
Division
Plants with more than one rooted crown may be divided and the crowns planted separately. Vegetable crop
propagated by crown division is Asparagus and rubarb. Asparagus propagation by division is one of the most
common methods. With several years production of spears slows down and the it become important to cut the
root into pieces and theses are again replanted to produce new plants. Roots from asparagus crown division
generally take a year to establish and produce spears. Rhubarb can be propagated from whole crowns or cut
pieces of the crown (divisions). Each division of the crown should possess at least one healthy bud. Crowns
should be planted as soon as possible after dividing to prevent them drying out. Rhubarb crowns and divisions
should be planted at a depth of 5 cm leaving 1 m distance between plants and 1.5–1.8 m between rows.
Although rubarb and asparagus can also be propagated by seeds but through division early produce can be
taken and it will be true to type.
(a) (b)
Figure 7. Root divisions of (a) Rubarb and (b) Asparagus
Suckers:Root suckers or root sprouts are plant shoots that arise from buds on underground roots or stems.
Suckers may also sprout from buds near the base of the parent plant and can grow into new plants. A number
of shrubs and trees propagate through sucker production. Globe artichoke (Cynara scolymus L.) is usually
vegetatively propagated from underground shoots known as 'ovoli' or from the suckers, stumps or dried shoots
from the previous growing season. Shoots should be selected from plants that produce well and should be
removed when they are about 20 cm in height. The shoots are removed by cutting the attachment to the
mother plant at the root with a sharp knife and gently loosening it from the soil and existing root ball. The
separated shoots should be planted in a freshly prepared bed to a depth of 15 to 20 cm and spaced 1.2 to 1.8 m
apart.
279
Figure 8. Suckers of Globe Artichoke
Grafting
Grafting is a method of propagation where two pieces of living plant tissues are joined together to develop as
a single plant. The first attempt in vegetable grafting was done by grafting watermelon (Citrullus lanatus)
onto pumpkin (Cucurbita moschata) rootstock in Japan and Korea in the late 1920s (Lee 1994). A serious
crop loss caused by soil-borne diseases aggravated by successive cropping was avoided by production of
vegetables with grafted seedlings (Kumar et al. 2015). In many fruit-bearing vegetables such as watermelon,
cucumber, melon, tomato, eggplant and pepper, the use of grafted seedling has become increasingly popular.
Grafting is an environment-friendly approach which is used to control soil borne diseases and increasing the
yield of susceptible cultivars (Lee and Oda 2003). This technique is eco-friendly for sustainable vegetable
production and by using resistant rootstock, it reduces dependence on agrochemicals (Rivard et al. 2008). To
induce resistance against low and high temperatures, grafts were generally used (Venema 2008). Grafting
increases the yield and promotes biotic/abiotic stress tolerance. A number of grafting techniques are employed
in fruit bearing vegetables. Tomato and eggplants are mostly grafted by cleft and tube grafting.Tongue
approach is used in grafting cucurbitaceae especially for cucumber. Slant-cut grafting is easier and has
recently become popular for watermelon and melon.
Micropropagation or In vitro propagation
Micro propagation is a fast method of plant propagation that has a great potential to develop high quality as
well as disease-free plants. For the rapid multiplication of plants, micro-propagation is a refined and well
adapted technique. Due to the fast speed of propagation it has a great profit-making potential, the high plant
quality and the ability to produce disease-free plants. It is an art and science of plant propagation under in
vitro conditions.The process of propagating plants includes several steps i.e. stock plant care, explant section
and sterilization, media manipulation to obtain proliferation, rooting, acclimatization, and growing plants in
field conditions. As it requires a sterile work-place, therefore micro propagation is usually done by hand
which makes the process cost-intensive and monotonous for the workers. Vegetable crop species have been
used extensively in tissue culture research. Notable examples include carrot cell culture and embryogenesis
research and potato protoplast manipulation and regeneration studies. Many reviews have elucidated the
application of cell, tissue, and organ culture techniques to vegetable crop species (e.g. Gleddie et al., 1987,
Glendening and Sjolund 1988, Gavinlertvatana et al. 1976).Relatively high multiplication rates can be
achieved as compared to the conventional vegetative propagation procedures. For example, annual rates of
multiplication in bulbs are generally below 5, whereas, micropropagation by adventitious shoot formation can
give multiplication rates of 10 to 1000 per annum. In some cases, rapid clonal propagation rates of 100,000 to
3,000,000 have been achieved through multiplication from apical or axially shoot. Propagation of such species
that cannot be propagated by conventional vegetative propagation methods can become possible. For example,
oil palm (Elaeis gluneensis) has been propagated from callus initiated from apical shoot tissue. Parents of
outstanding F1hybrids can be multiplied and used for hybrid seed production, this is particularly useful in
such cases where the parents are difficult to multiply because of self-incompatibility (e.g., cauliflower). The
technique permits propagation of high-value unique lines, e.g., seedless, gynoecious species, male sterile lines,
etc. Tissue cultures are also useful for maintaining special genotypes used in breeding, this attribute is
particularly important if the performance of progeny from a cross is not known until several years later (e.g.,
forage species like alfalfa or tree species). In addition, in vitro propagation alone or together with heat therapy
280
can be used to produce disease-free plant materials, which is preferred for international germplasm exchange.
Round the year propagation is possible without environmental effects.
Conclusion
Propagation is an important technique of multiplying useful plants. Vegetable crop plants are propagated by
seeds or vegetatively using plant parts like leaf, stem, tubers, roots etc. to generate a new plant. Grafting is
also being used these days in some vegetable crops like tomato, brinjal and watermelon to impart disease and
stress resistance. Micropropagation also play an important role in the rapid production of disease free planting
material. Two objectives of propagation are to achieve an increase in numbers and to preserve
the essential characteristics of the plant. Seed propagation is ideal to achieve success in breeding programmes,
to exploit hybrid vigour whereas asexual or vegetative propagation is important to maintain the characteristics
of a genotype in its pure form. The study and knowledge of these methods is important in order to get
information to produce healthy planting material on a large scale with precise use of inputs and time saving.
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Summary Stem cuttings of potato placed in moist sand in the greenhouse developed roots within 2 weeks. The rooted cuttings when transplanted to the field became vigorous and high yielding plants. Stem cuttings were used to obtain rapid and extensive increase of desirable sub-clones.