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38 Textbook of Pharmacognosy
price and this limits the present large scale cultivation of medicinal plants.
To overcome all these hurdles, there is an urgent need for the cultivation
of medicinal plants.
CULTIVATION
Cultivation is always advantageous over collection from wild habitat,
because of the following reasons. Cultivation always ensures the purity
and the quality of crude drugs. If all the operations of cultivation are
maintained uniformly, one can obtain the drug of the highest quality.
Cultivation of medicinal plants with rhizomes requires an adequate
quantity of fertilisers and suitable irrigation. Proper cultivation always
results in the production of a crop with maximum content of volatile oil
and other constituents like ginger, turmeric and licorice. In the absence of
the weeds, the crude drug contamination can be avoided. If all the
operations are carried out by the skilled and experienced professional
personnel, the drugs of higher therapeutic quality in addition to a higher
yield can be obtained. Cultivation also helps in a continuous supply of the
crude drug to the market so that the industries that depend on the drugs
do not face a shortage. Medicinal and aromatic plant cultivation like coffee,
tea, opium and cinchona also leads to establishment of many cottage and
small scale industries and industrialisation. The higher prices of the crude
drugs as well as losses due to environmental imbalance like storms, floods,
droughts, etc. are the only disadvantage. Cultivation permits the scientists
to apply modern methods of technology like mutation, polyploidy and
hybridisation to achieve greater yields and to produce many more new
drugs.
Medicinal plants are propagated by the usual methods of propagation
which remain applicable to normal crops like sexual method (seed
propagation) and asexual method.
In sexual method, the seedlings are raised from healthy seeds of a
superior quality. The seeds must possess a high percentage of germination
and they must be free from disease and pests. The seeds must be subjected
to scarification prior to germination and when not in use they must be
properly stored in cool and dry place to retain their power for germination
but not for a longer time. Prior to germination they must be exposed to a
chemical treatment with substances like gibberellins, cytokinins, ethylene,
thiourea, potassium nitrate, sodium hypochlorite. Gibberellic acid relieves
dormancy of the seeds and promotes the growth of seedlings. Dormant
seeds from a fresh harvest germinate immediately if they are soaked in
potassium nitrate solution. Thiourea promotes germination in seeds which
fail to do so in dark or at higher temperatures. In some cases, special
treatment is given such as soaking in water for a day (castor seeds) or
soaking in sulphuric acid (henbane seeds) or subjected to pounding with
Cultivation, Collection, Processing, Drying and Storage of Medicinal Plants 39
coarse sand (Indian senna seeds) to partially remove their outer seed coat.
This method is advantageous because, the seedlings have a longer life,
easy to raise and cheaper. The propagation sometimes also results in the
production of plants of superior quality by chance (as in Papaya and
Orange). This method has also its own limitations such as: the trees raised
from seedlings are not uniform in their growth and yielding potential and
require more time to bear the fruit and the cost of harvesting is more.
In asexual method, the vegetative part of a plant (stem or root) is placed
in a suitable environment that it develops into a new plant. This has some
advantages like: the new plants do not show any variation from which the
plant part has been collected, the plants maintain uniformity in their growth
and yielding capacity, and in fruit trees, uniformity make harvesting and
marketing easy. This method helps to generate the seedless fruits as in
grapes, pomegranate and lemon. Plants bear the fruits earlier to those
produced sexually. There is a possibility of generating the disease resistant
varieties (by budding or grafting). This method has its own disadvantages
too. The asexually generated plants are not long lived and do not show
vigorous growth unlike the sexually produced ones. There is no possibility
of evolving new varieties. Asexual method can be achieved either by
vegetative propagation or by aseptic method. Vegetative propagation is
carried out by means of underground stems like bulbs (squill and garlic),
corms (colchicum and saffron), stem tubers (aconite and potato) and
rhizomes (ginger and turmeric). It can also be carried out by means of subaerial stems like runners (mentha), suckers (chrysanthemum, pineapple
and banana), offsets (aloe and valerian) and stolons (arrow root and
licorice). Aseptically, the medicinal plants are micropropagated on an
artificial medium under aseptic conditions from cell, tissues, organs,
embryos, seeds, pollen and root and shoot apices, etc. They are also supplied
with external nutrients, hormones, etc.
The Factors Influencing the Cultivation of Medicinal Plants
The factors that affect cultivation of medicinal plants can be listed as:
cultivability, climatic (external) factors, edaphic (soil) factors and others
like application of fertilisers and pesticides.
a. Cultivability: The medicinal plants do grow in a wild state but the
cultivation of the wild varieties involves many factors. Some plants
like opium, flax and cocoa have been cultivated since ages. Certain
types of plants like Indian hemp, ginger, cardamom, cinchona, linseed,
etc. are exclusively cultivated. When the wild plant supply falls short,
cultivation is enforced. Such plants may be either growing or being
cultivated in distant geographical regions and the transportation of
such drug may involve excessive economy or if tried to cultivate in a
different geographical region they may fail to acclimatise and
40 Textbook of Pharmacognosy
establish successfully. The cultivation of medicinal plants is preferred
to maintain the natural resources intact and also to improve the
quality of the drug. Another reason is that a specific variety or a
species may need to be cultivated as it is not freely accessible in nature.
The collection is to be done at a precise growing period when the
active principle is supposed to exist at its peak. It is not possible to
know when the product will be at its peak if the desired plant is
allowed to grow in a wild state, in nature. But, some plants such as
the rubber plant luxuriant in Amazon basin are unwieldy for
cultivation as it never grows in the cleared areas.
b. Climatic Factors: The climatic factors that influence the chemical
content, growth and yield of a medicinal plant are altitude,
temperature, rainfall (irrigation), humidity (moisture content) and
light.
1. Altitude: Altitude at which the medicinal plants are cultivated
is an important factor. Plants like cinnamon are grown from
250–1000 meters, cardamom is grown from 600–1600 meters,
cloves are grown up to 900 meters, saffron is grown up to
1250 meters, cinchona and coffee from 1000–2000 meters and
camphor from 1500–2000 meters from sea level while senna is
cultivated at the sea level.
2. Temperature: Temperature is another major factor which
regulates the overall growth of the plant. For example, the
tropical and sub-tropical plants of the temperate regions of the
globe grow well in summer rather than in winter because they
are not frost resistant. The higher temperatures in general
promote the formation of volatile oils but the hot days may
account for the physical loss of the oil. For example, the
optimum temperatures required for species like cardamom
o
varies between 50 and 100
cinchona between 60 and 75
o
and 90
F. Some plants like camphor and coffee cannot
F, for coffee between 55 and 70oF, for
o
F and for tea it varies between 70
withstand frost while saffron grows best in a cold climate and
dry weather is required for pyrethrum.
3. Rainfall/Precipitation: The rain fall or precipitation includes many
factors like annual rainfall, its distribution throughout the year, its
effect on the humidity and water holding capacity of the soil. For
example, continuous rain leads to the loss of water-soluble
alkaloids (in solanaceae) from the roots and their leaves get
leached, thereby resulting in the low yield of the active constituents
in the wet season of the year. Most of the cultivated medicinal
plants require proper irrigation or a sufficient amount of rainfall
except xerophytes like aloe, acacia, etc.
Cultivation, Collection, Processing, Drying and Storage of Medicinal Plants 41
4. Light: The influence of light is not the same in all plants. The plants
in the wild usually grow under shade. When these are to be
cultivated, the required shade is to be necessarily provided. It is
observed that full sunshine promotes the content of alkaloids in
belladonna, stramonium and Cinchona ledgeriana. The leaves of
mentha showed menthane, menthol and traces of menthofuran
under long day conditions while under short days, showed
menthofuran as a major constituent. Specific day length is capable
of initiating the flowering in many plants and this should be taken
into account during the cultivation of medicinal plants for drugs
from their flowers.
c. Edaphic (Soil) Factors
1. Soil factors (nature of soil, soil pH, soil moisture and soil
nutrients): Soil supports the growth of plants by providing the
anchorage for their roots and also water and essential mineral
nutrients for their growth. The growth of the plants is dependent
upon the arrangement of the soil particles, nature and size of the
soil particles, the amount of organic matter and soil biota. The
porosity of the soil and the pH of the soil solution also determine
the growth and development of the plants. The physical and
chemical properties of the soil greatly influence the growth of
plants. Soil fertility plays a major role in providing the balanced
proportions of nutrients to plants. Mucilage used as a water
retaining material is produced by Althaea officinalis and it has been
observed that in Western Europe where the soils are mostly clayey,
when grown on the soil with high moisture content, the plant
contained lesser amount of mucilage. Similarly, all species cannot
tolerate the same soil pH and the limit varies from plant to plant.
For example, Datura stramonium has a pH tolerance of 6.0–8.2 while
Majorana hortensis shows a tolerance limit of 5.6–6.4. Normally, the
plants that contain the essential oils like Mentha piperata and those
that contain the alkaloids such as Datura stramonium seem not to be
influenced by the variations in soil pH. All plants require calcium
for their normal nutrition and growth but, Digitalis purpurea, Pinus
pinaster, etc. fail to grow on calcareous soils. Hence, a thorough
study on the effect of various mineral nutrients on medicinal plant
growth is needed, and with a better understanding of the plant
responses, better yield of the crude drugs can be achieved.
2. Additive factors (fertilisers, pesticides, etc.): Fertilisers and
manures play an important role in plant nutrition as the addition
of the same to a soil make it fertile. The addition of chemical
fertilisers to the soil in which medicinal plants are cultivated
supplies all the necessary primary and secondary nutrients as well
as the trace elements to plants. The addition of manures like farm
42 Textbook of Pharmacognosy
yard manure (compost), poultry manure, castor and neem seed
cake, vermicompost in addition to bone meal, fish meal, biogas
slurry, blood meal and press mud makes the soil rich in organic
and inorganic nutrients required by the plants. The addition of
biofertilisers like Rhizobium, Azotobacter, Azospirillum, Beijerinckia,
Cyanophytes, Azolla, etc. are preferred in place of organic and
inorganic manures as they are cost-effective and also harmless to
the plants cultivated. A considerable amount of the crude drug
may be lost by pests before it reaches the consumer after harvest.
Hence, pest control assumes primary importance in the context to
cultivation of medicinal and aromatic plants. The common pests
like fungi, viruses, insects, weeds, rodents, etc. are to be controlled
by the use of specific pesticides, weedicides, rodenticides,
insecticides, acaricides, herbicides, antifungal and antiviral
substances either by mechanical, chemical or biological control
methods to enhance the quality and quantity of the crude drug
during cultivation. The use of biopesticides is highly preferable.
COLLECTION AND PROCESSING OF CRUDE DRUGS
The drugs are to be processed prior to marketing after collection. Several
methods are adapted in the preparation of the drugs and also to meet the
standard pharmacopoeial requirements. These include methods of
collection, harvesting, drying, dressing, packing and storage.
1. Collection: The crude drugs can be collected either from wild species
or cultivated varieties, and the collection can be done either by native
labourers without a skill or by scientifically trained skilled workers.
a. Time of collection: The different parts of the plants that contain the
crude drugs and drug material are to be collected with some
knowledge associated with the time of collection and the nature of
the plant parts at which time the components will be at their peak
stage of accumulation. The prevailing environmental conditions
are taken into consideration while collecting the crude drugs. The
drugs from the leaf and flower tops like senna, vinca, belladonna
and digitalis should be collected before the flowers open up or just
before they reach their maturity. Similarly, the leaves of aloe can
be collected when they are fresh and succulent for their mucilage.
saffron, unopened flower buds of cloves, chamomile and arnica
should be collected prior to pollination before their full expansion
during morning in dry weather. The bark is to be collected
preferably either in spring or early summer during which period
the cambium will be very active which becomes easier for
collection by detachment except the bark of wild cherry and the
bark of cinnamon which are to be collected in autumn and in rainy
Cultivation, Collection, Processing, Drying and Storage of Medicinal Plants 43
season respectively. The fruits for drugs are collected when they
are mature and fully grown. For example, the fruits of cardamom
are collected before they dehisce, tamarind fruits when they have
attained full maturity and the fruits of caraway and coriander
when they are fully ripe. The roots for the crude drugs are to be
collected in spring season before their vegetative growth comes to
a halt. Similarly, the rhizomes are collected when the food reserves
are full. The unorganised drugs like resins, gums and latex are
collected as soon as they begin to ooze out from the plant parts.
Acacia gum is generally collected 2–3 weeks after making the
incisions on the bark of the tree and opium, papaya are collected
after the latex gets coagulated.
b. Method of collection/harvesting: Harvesting is done with
efficiency by employing skilled workers. If the crude drugs are
underground like roots, tubers, rhizomes, etc. they are to be
harvested by mechanical devices like diggers. Drugs which
are aerial are to be harvested by binders. The flowers, seeds, fruits
are to be harvested by seed strippers. The cloves are collected by
beating the plant with bamboos. The cochineal insects are collected
by brushing. The seaweeds are harvested by forks. Mint is
harvested by mowers while fennel and coriander are uprooted and
dried followed by thrashing and winnowing.
In the case of unorganised drugs where the concerned part of
the medicinal plant is underground, it should be made free from
the soil. The part possessing the crude drug is to be shaken
thoroughly and it may be brushed during and after drying which
separates the soil particles that are stuck. In the case of valerian, the
particles of clay are removed by washing it in the streams where it
grows. If the part is diseased, it should be discarded. In case of
ginger and marsh mallow, the rootlets are to be peeled off. If the
underground organs are large in size as in calumba root, they are
cut into slices for drying. The seeds of nux vomica and cocoa are to
be carefully extracted from the mucilaginous fruits and thoroughly
washed to make it free from the pulp.
2. Drying: Drying is an integral part of the drug collection. The plant
materials that contain the crude drug after collection need to be dried
for storage and transportation. The application of a uniform type of
drying procedure is not possible in all medicinal plants since the
chemical constituents of the collected material vary in their
composition. For example, slow drying preferably at lower
temperature is carried out to ensure enzyme action in the seeds of
cocoa, roots of gentian and in the rhizomes of Orris. The plant
materials containing the volatile oils need to be dried immediately lest
44 Textbook of Pharmacognosy
they lose their aroma. Immediate drying is taken up as moist drugs
tend to develop moulds and if so they are to be discarded.
There is a considerable variation in the type of the drying process.
Plants like cardamoms, cloves and cinnamon, etc. are air-dried. As the
open air drying depends on the weather, the drying time is to
be carefully selected. In countries like West Africa with a high
humidity in the atmosphere, artificial rapid drying of the material is
desired. In European countries, continuous felt driers are used for
drying the bulk of drugs as in digitalis. For the procurement of
nutmeg, drying is done by open fire. The process of drying is carried
out in drying sheds where trays containing the materials are arranged
with a gap of 15 cm to ensure the circulation of free air in between
them.
3. Dressing (garbling): This includes the removal of sand, dirt and
extraneous matter (foreign organic matter) of the same plant that does
not constitute the drug. In lobelia and stramonium, extra portions of
the stems are removed and in cloves, the stalks are separated. The
roots, rootlets and stem bases are carefully removed in the case of
rhizomes constituting the drug.
4. Packing: While packing the drugs, the nature of the drug and the
nature of the climate during transportation and storage should be
taken into consideration to retain the quality of the drug until it
reaches the consumer. For example, aloe is packed in goat skin,
balsam is packed in kerosene tins and asafoetida is stored in wellclosed containers. Cod liver oil is stored in dark containers to
prevent the effect of sunlight while leaf drugs like senna, vinca are
pressed and stored as bales. Colophony is packed in big masses to
prevent auto-oxidation and cinnamon is packed in quills. Drugs like
roots and seeds are packed in gunny bags as they do not need special
attention. Some others are stored in bags internally coated with
polythene.
5. Storage/preservation: The crude drugs after collection and drying
need to be properly stored to maintain their original from intact and
also to maintain a high quality over a longer period until they are
transported to the market.
The crude drugs are highly susceptible to physical and chemical
deterioration if they are not properly stored or preserved. The
physical factors like humidity, light, temperature and oxygen bring
down and reduce the quality of the drug during storage/preservation.
Drugs are stored usually in containers like sacks, bales, wooden cases,
paper bags, cardboard, boxes, etc. The drugs are stored in waterproof, fireproof and rodent-proof premises. The crude drugs that are stored reabsorb
Cultivation, Collection, Processing, Drying and Storage of Medicinal Plants 45
about 10–12% of moisture from the surroundings which may bring about
enzyme activation to decompose the active constituent within. If the store
house is saturated with moisture of >75%, the material like starch, gentian,
squill and gelatin get degraded. Similarly, the soil with which the storage
cellars are made of also affects the quality of the drug. The clay soil absorbs
atmospheric moisture and hence, such cellars need artificial heating to
reduce their humidity, while the sandy soil of the cellar loses its moisture
content and keep the drug material dry. The material like digitalis and
Indian hemp should never be allowed to air dry as they lose their activity
to some extent and such drugs should be kept in sealed containers along
with a dehydrating agent. The volatile oils should be stored in sealed and
well-filled containers in a cool dark place to retain their quality for a longer
time.
Light also affects the crude drugs. For example, rhubarb rapidly changes
to a reddish tint from yellow, coloured or white flowers of Rose will turn
brown and those of santonin become black. Added to colour change, the
glycosides and vitamins too get decomposed at a slower pace. The volatile
oils of chamomile flowers, ginger and asafoetida, etc. are affected by
changes in temperature.
Direct oxidation by oxygen of the air too brings about changes in the
constituents of the crude drugs. For example, linseed oil, cannibal of Indian
hemp, etc. develop a thick consistency and get resinified. Sometimes, the
form or the shape of the drug also plays an important role in the storage
and preservation. For example, colophony in its entire form (as big masses)
is well-preserved rather than in its powdered form when it gets oxidized
and loses its solubility in ether. Similarly, squill if preserved in its powdered
form becomes rubbery on prolonged exposure to air and the fixed oil in
powdered ergot becomes rancid on storage.
The preservation of the drug in such a way that they are not exposed to
the attack of the insects or molds is also important. Different types of insects,
nematode worms, molds and mites may infest the crude drugs during
storage. Hence, every precaution is to be taken to retain the quality and
quantity of the drug. The common insect pests include the members of
coleoptera (Stegobium and Calandrium), lepidoptera (Ephestia and Tinea) and
arachnida (mites like Tyroglyphus and Glyophagus). The premises of storage
and the cup-boards must be periodically fumigated and kept exposed to
open air and away from flame when carbon disulphide is used as a
fumigant. Cold storage is also a safe means of storage. The drug material
is kept in numerous small sealed containers to avoid exposure of the entire
drug to humid atmosphere. They can also be preserved in well-closed
opaque containers. The methods of preservation of the drug material vary
with the form and nature of the drug preserved. If the crude drugs are not
properly preserved keeping their active constituent in form or exposed to
partial pathogenic or pest attack, the purpose of drug is lost.
46 Textbook of Pharmacognosy
PLANT HORMONES AND THEIR APPLICATIONS
Compared with animals where the nervous system mediates cell to cell
regulation, in plants such a function is through the vascular system which
transports certain regulators. The hormones are organic substances that
act as messengers for such regulation needed in small quantities and their
sites of action and biosynthesis are different. Plant hormones (plant growth
regulators or plant growth substances) are the naturally occurring organic
substances other than the nutrients which control the growth processes
(morphological and physiological) in their lower concentrations. These
include both exogenous (synthetic) and endogenous (native) substances
which can modify growth in plants. Most of the plant hormones exhibit a
broad action spectrum and thus a single hormone may influence several
processes.
The native plant growth substances include auxins, gibberellins,
cytokinins, abscisic acid and ethylene. These regulate cell division, cell
enlargement, cell differentiation, organogenesis, senescence and dormancy.
These are at present employed in tissue cultures as such it is possible to
culture any part of the plant in vitro. These are capable of enhancing
production of the secondary metabolites which are used as drugs.
1. Auxins: Auxin is a general term that indicates all the substances which
promote the elongation of the coleoptile tissues. Auxins may be
natural (produced by the plants) or synthetic (artificially produced)
and they have the same action. IAA (indole 3-acetic acid) is the
principal natural auxin and it was F. W. Went (1928) who provided
experimental evidence for IAA from the tips of Avena coleoptile,
which is now popular as went curvature test. Other natural auxins are
IAN (indole 3-acetonitrile), 4-chloroindole 3-acetic acid and phenyl
acetic acid. The synthetic auxins include IBA (indole 3-butyric acid),
NOA (2-naphthoxy acetic acid), NAA (alpha-naphthyl acetic acid),
NAD (1-naphthyl acetamide), 2,4-D (2,4-dichlorophenoxy acetic acid),
2,4,5-T (2,4,5-trichlorophenoxy acetic acid), 2,4,6-T and 5-carboxymethyl-N, N-dimethyl dithiocarbamate.
Auxins are associated with cell and internodal elongation, apical
dominance, leaf growth, initiation of the vascular tissues, increased
cambial activity, formation of the fruit without pollination
(parthenocarpy), growth of the fruits, inhibition of the root growth
and leaf abscission, photo and geotropism, etc. The mechanism of
their action is by interaction with one or more components of protein
synthesis. It is also suggested that they alter the osmotically active
contents of the vacuole during expansion and extension of the cell wall.
IBA is a promising growth regulator which induces rooting in
cinchona, pinus, papaya and coffee. IAA, NAA and 2,4-D when added
Cultivation, Collection, Processing, Drying and Storage of Medicinal Plants 47
to cultures of ergot increases the content of indole alkaloids. Seedlings
of Mentha piperita treated with NAA showed about 40% increase in
their content of volatile oil. 2,4-D and 2,4,5-T are potent weedicides in
higher concentrations.
2. Gibberellins: These are a class of natural plant growth regulators
which stimulate cell division or cell elongation or both, promote
vegetative growth, growth of the fruits, help in breaking dormancy,
initiate the flower formation and induce parthenocarpy in the absence
of pollination to result in the seedless fruits. They also promote rapid
expansion of plant cells, stimulate seed germination, and break
dormancy due to over-wintering, and influence increase in stem
elongation and increase in the size of the leaves. The effects are marked
in the intact plants rather than excised organs such as auxins. So far 56
gibberellins are known out of which 52 have been positively spotted
from Gibberella fujikuroi and/or higher plants and others from fungi.
Gibberellins were discovered from a pathogenic fungus, Gibberella
fujikuroi (formerly Fusarium heterospermum) on rice by a Japanese plant
physiologist, Kurosawa. Paleg identified that their biological activity
was due to the presence of a gibbane skeleton. Extensive research on
gibberellins has shown that gibberellin-A (isolated in 1938) is a mixture
of 6 gibberellins referred to GA
, GA2, GA3, GA4, GA7 and GA9 out of
1
which GA3 is the most common gibberellin of universal occurrence
and is called gibberellic acid. The different groups of plants contain
different types of gibberellins and all of them together will not occur
in the same plant.
Gibberellins find their application in medicinal plants. Gibberellins
in lower concentrations increase the yield of glycosides in digitalis
(digoxin). In case of senna, GA increases the dry weight of the shoot
but reduces the content of sennoside in the leaves. Castor plants treated
with GA increased their height 5 times more but failed to show any
change in the content of the fixed oil. GA reduces the alkaloid content
in vinca, Datura and hyoscyamus. GA induces the activity of
gluconeogenic enzymes in the early stage of germination which ensures
a rapid conversion of lipid to sucrose which is rapidly utilised in the
development of the root and shoots in the embryo. In monocot seeds,
gibberellins induce the synthesis of amylase and other hydrolases
during the germination and the formation of the seedling.
3. Cytokinins (cytokinetins or phytokinins): Phytokinins are the purine
derivatives especially from adenine. Either natural or synthetic
cytokinins regulate growth by promotion of cell division and leaf
senescence, sometimes promoting the development of lateral buds and
inhibiting senescence. They also participate in embryo and seed
development and influence the expansion of cells in leaf discs and