Vavilov's Centres of Origin and Crop Domestication

WELCOME TO ECONOMIC BOTANY
Origin of Cultivated Plants : Concept of Centres of Origin,
their importance with reference to Vavilov’s work.
Examples of major plant introductions; Crop
domestication and loss of genetic diversity; evolution of
new crops/varieties, importance of germplasm diversity.
By
N. Sannigrahi, Associate Professor,
Department of Botany,
Nistarini College, Purulia (W.B) India

INTRODUCTION
 The basic needs of the human beings are food, clothing &
shelter. The all the above indispensible items are obtained
from plants directly or indirectly. The angiosperms along with
many fungi, algae, bryophytes, pteridophytes and
gymnosperms play a very crucial role to address the above
needs of the civilization. They can be grouped as follows:
 Food plant cereals
 Legumes for pulses Nuts
 Fruits of diverse types
 Fiber yielding plants
 Tannins and Dyes
 Rubber and its diverse products
 Fatty oils & vegetable fats,
 Essential oils

ECONMIC BOTANY
 Organic acids
 Sugar yielding Plants
 Pulp & paper
 Gums & resins
 Mucilage
 Proteins
 Medicinal plants and drugs
 Food adjuncts
 Apart from these , there are also many plants of great
economic importance which are directly used from the plants
or by the processing , different secondary products are
available and all these substances are used for the
development of civilization and to drive the wheel of
economy of any country. The plant or plant parts used for the
welfare of human beings are addressed in the domain of
economic Botany.

PRIMARY AND SECONDARY ORIGIN
 All the agricultural crops have been originated from
would ancestor but it is very difficult to find out the wild
ancestors and loci of the domestication of economic
important plants as most of them were developed in the
remote past. Many started to domesticate the crops in the
ancient pasts. De Candolle ( 1883) used many
archeological and ethnological data, historical findings
and philogy to determine the origin and the spread of the
cultivated plants used in the recent times. But it is
generally accepted that cultivated plants were not
distributed uniform throughout the world and even today,
certain regions show greater diversity than other
cultivated crop plants. These areas are called the primary
centre of origin and those plants showing considerable
diversity in forms but not being originated there are
treated as secondary centre of the origin of that species.

CROP DOMESTICATION
 The centre of origin is a geographical area where the particular
group of organisms (either domesticated or wild) first
originated on earth. Many people believed that centers of origin
are also centers of diversity. But, the centers of diversity may
not represent the centers of origin of crop plants. Although a
few species may have been originated separately at more than
one place, but most species had their origin at a certain place
and then spread elsewhere. In other words, in the centre of
origin a crop is generally confined to one place, whereas the
centre of diversity may be found at more than one place. The
exact location of origin of species is only a matter of
speculation based on indirect evidences. The information on
origin of crop plants is important in plant breeding to locate
wild relatives, related species and new genes. Knowledge of
the origins of crop plants is important to avoid genetic erosion,
the loss of germplasm due to the loss of ecotypes and habitat.

VAVILOV SYNDROME
 The Russian scientist Nikolai Ivanovich Vavilov and his
colleagues visited several countries and collected a large
number of crop plants and their wild relatives. They used this
collection in Russian breeding programme of developing
improved varieties. His deductions were based on evidences
from morphology, anatomy, cytology, genetics, plant
geography and distribution. He considered that great centers of
origin were always located in lower mountains and hills of
tropical, sub-tropical regions. He also recognizes some
secondary centers of origin where two or more species crossed
together. Secondary centers of origin are the places where
natural and artificial selection occurred on after another. He
stated that plants were not domesticated at random but it was a
continuous process.

VAVILOV CENTRES OF ORIGIN
 1. Chinese centre: It is considered to be one of the
earliest and largest independent centers of origin of
cultivated plants. This centre includes mountain
regions of central and western China. The endemic
species listed from this centre include Soya bean,
radish, Turnip, Pear, Peach, Plum, Colacasia,
Buckwheat, opium poppy, brinjal, apricots, oranges,
china tea etc.
 2. Himalayan centre: It also known as the Indian
centre of origin. This centre includes regions of Assam,
Burma, Indo-china and Malayan Archipelago. The
endemic species listed from this centre include Rice,
red gram, chick pea, cowpea, Mung dal, brinjal,
cucumber, sugar cane, black pepper, Moth bean, rice
bean, cotton, turmeric, indigo, millets etc

 3.Mediterranean centre: This centre includes borders of
Mediterranean Sea. Most of the cultivated vegetables have their
origin in this region. The endemic species listed from this
centre include Durum wheat, emmer wheat, oat, barley, lentil,
pea, grass pea, broad bean, cabbage, asparagus, pepper mint
etc.
 4. Abyssinian centre: This region includes Ethiopia and parts of
Somalia. The endemic species listed from this centre include
Wheat, sorghum, bajra, safflower, castor, broad bean, okra,
coffee etc.
 5. Central Asian centre: This centre includes north-west India,
Afghanistan, Uzbekistan and western China. The endemic
species listed from this centre include Bread wheat, club wheat,
sesame, linseed, muskmelon, carrot, onion, garlic, apricot,
grape, hemp, cotton etc

 6. Asia minor centre: This centre covers near East Asian
regions like Iran and Turkmenistan. The endemic species listed
from this centre include Wheat, rye, Pomegranate, Almond,
Fig, Cherry, Walnut, Alfa Alfa, Persian clover etc.
 7. Central American centre: This centre includes southern parts
of Mexico, Costa Rica, Guatemala and Honduras region. The
endemic species listed from this centre include Maize, rajma,
lima bean, melon, pumpkin, sweet potato, arrow root, chilly,
cotton, papaya, guava, avocado etc.
 8. South American centre: This centre includes Peruvian
regions, islands of southern Chile, Brazil and Paraguay regions.
The endemic species listed from this centre include Potato,
sweet potato, lima bean, tomato, papaya, tobacco, quinine,
cassava, rubber, Ground nut, Cocoa, pineapple etc

LIMITATIONS OF VAVILOV
 The expansion of our understanding on cultivated plants
pointed certain limitations on Vavilov’s views. These views
require some modifications, 1. Vavilov considered the region
with greatest genetic diversity of a species as the centre of
origin of that species. But now, many such species are known
whose centers of origin and genetic diversity are different. For
example, Maize and Tomato
 2. The centers of origin of cultivated plants as per Vavilov are
limited to the mountains and small hills in tropical and sub-
tropical regions. But recent evidences also suggest plains as the
centers of origin of many cultivated plants.
 3. Today several crops are known whose centers of origin are
different from the ones suggested by Vavilov. Moreover there is
more than one centre of origin. Also, the origin of many of the
species cannot be traced due to lack of sufficient evidence

MAJOR PLANT INTRODUCTIONS
 Plant introduction is a process of introducing plants (a
genotype or a group of genotypes) from their own environment
to a new environment. The process of introduction may involve
new varieties of crop or the wild relatives of crop species or
totally a new crop species for the area. The process of plant
introduction is the successful compliance of two important
aspects, viz., domestication and acclimatization. Domestication
is the process of bringing of a wild species under cultivation by
making them changed in behavior suitable for new
environment.
 Acclimatization is the ability of a crop to become adapted to a
new climatic and edaphic condition.

PRIMARY & SECONDARY
 Primary Introduction: When the introduced variety
is well suited to new environment then it is released
for commercial cultivation without any alteration of
genotype. For example, dwarf wheat varieties like
‘Sonora-64’, ‘Lerma rojo’ and dwarf rice varieties like
‘Taichung Native 1’, ‘IR-8’ are the examples of primary
introduction.
 Secondary introduction:
 When the introduced variety is subjected to Selection
or used in hybridization programme with local
varieties to get the improved varieties with some new
characters introduced called secondary introduction.
For example, the varieties like ‘Kalyan Sona’ and
‘Sonalika’ of wheat have been selected from material
introduced from CIMMYT, Mexico.

CROP DOMESTICATION & LOSS OF GENETIC
DIVERSITY
 Crop domestication is the process of artificially selecting
plants to increase their suitability to human requirements:
taste, yield, storage, and cultivation practices. There is
increasing evidence that crop domestication can profoundly
alter interactions among plants, herbivores, and their natural
enemies. The process of crop domestication is driven by human
selection, cultivation practices, and agricultural environments.
Any selection imposes the reduction of diversity in genomic
regions controlling desirable traits, such as non-shattering
seeds or increased palatability. Furthermore, agricultural
practices greatly reduced effective population sizes of crops,
allowing genetic drift to alter genotype frequencies, including
the random loss of alleles.

DOMESTICATION & GENETIC EROSION
 Domestication implies the action of selective sweeps on
standing genetic variation, as well as new genetic variation
introduced via mutation or introgression. Furthermore, genetic
bottlenecks during domestication or during founding events as
crops moved away from their centers of origin may have
further altered gene pools. To date, a few hundred genes and
loci have been identified by classical genetic and association
mapping as targets of domestication and post domestication
divergence. However, only a few of these have been
characterized, and for even fewer is the role of the wild-type
allele in natural populations understood. After domestication,
only favorable haplotypes are retained around selected genes,
which creates a genetic valley with extremely low genetic
diversity. These “selective sweeps” can allow mildly
deleterious alleles to come to fixation and may create a genetic
load in the cultivated gene pool.

LOSS OF GENETIC DIVERSITY
 The term biodiversity was coined by Walter and Rosen (1985)
and is the abbreviated word for Biological Diversity. Life
originated on earth almost four billion years ago and nature
took more than 1 billion year to develop this wide and complex
spectrum of life on earth. Scientists believe that the total
number of species on earth is in between 10-80 million (Wilson
1988) of which 1.4 million species have been enlisted so far.
 i) Biodiversity is the variety of life in all its forms, levels and
combinations. It includes species diversity, genetic diversity
and ecosystem diversity (International Union for Conservation
of Nature and Natural Resources—IUCN, United Nations
Environment Programme—UNEP and World Wildlife Fund—
WWF 1991).

BIODIVERSITY-DEFINITIONS
 ii) United Nations Earth Summit in Rio de Janeiro defined
biodiversity as – The variability among living organisms from
all sources, including terrestrial, marine and other aquatic
ecosystems and the ecological complexes of which they are
part. This includes diversity within species, between species
and of ecosystems.
 (iii) According to U.S. Congressional Biodiversity Act –
Biological Diversity is the variety and variability among living
organisms and the ecological complexes in which they occur
and encompases ecosystem diversity, species diversity and
genetic diversity. iv) In the simplest terms, biological diversity
is the variety of life and its processes and it includes the variety
of living organisms, the genetic differences among them and
the communities and ecosystems in which they occur.

TYPES OF BIODIVERSITY
 Biodiversity is usually studied at three different levels—Species
diversity, Genetic diversity and Ecosystem diversity. It actually refers
to species richness, in terms of number of species in a site or habitat.
Global diversity is typically represented in terms of total number of
species of different taxonomic groups. As mentioned before, an
estimated 1.4 million species have been identified to date. Species
diversity, again, is studied at three levels: alpha diversity (number of
species coexisting at a site), beta diversity (difference in species
complement between patches) and gamma diversity (number of
species in a large area, e.g. a country). This series can further be
extended to delta diversity for biomes (biomes are climatically and
geographically defined areas of ecologically similar climatic
conditions such as communities of plants, animals and soil organisms
and are often referred to as ecosystems) and omega diversity for the
entire biosphere.

CAUSES OF LOSS OF GENETIC DIVERSITY
 Alteration and loss of the habitats: The transformation of the
natural areas determines not only the loss of the vegetable
species, but also a decrease in the animal species associated to
them.
 Introduction of exotic species and genetically modified
organisms: Species originating from a particular area,
introduced into new natural environments can lead to different
forms of imbalance in the ecological equilibrium. Refer to,
“Introduction of exotic species and genetically modified
organisms”.
 Pollution: Human activity influences the natural environment
producing negative, direct or indirect, effects that alter the flow
of energy, the chemical and physical constitution of the
environment and abundance of the species.

 Climate change: For example, heating of the Earth’s
surface affects biodiversity because it endangers all
the species that adapted to the cold due to the latitude (the
Polar species) or the altitude (mountain species).
 Overexploitation of resources: When the activities connected
with capturing and harvesting (hunting, fishing, farming) a
renewable natural resource in a particular area is excessively
intense, the resource itself may become exhausted, as for
example, is the case of sardines, herrings, cod, tuna and many
other species that man captures without leaving enough time
for the organisms to reproduce.
 The introduction of invasive species is the tremendous
threat to biodiversity crisis. The species, which is not
native to the ecosystem, arrives or is introduced mostly
via humans in the

 new ecosystem and start to pullulate is called as invasive species.
Such species are detrimental as they effect the ecosystem
disproportionately compared to any other species. Most of the new
species introduced in the ecosystem do not become invasive, but few
of them turn into invasive species and adversely affect the
ecosystem.
 Natural catastrophes, for instance volcanoes, wildfires, floods,
hurricanes, draughts, epidemics, tsunamis etc. cause a heavy loss of
biodiversity . In humid tropical areas such as central Africa, eastern
and northern Australia, some areas of South America floods are
common. The tropical areas harbor lot of vegetation and vast number
of animals survive in the vegetation. Due to flooding, large amount
of nutrients from the soil gets washed away. Drought too led to dry
soil and decline in the level of water table [29]. In this situation, both
animals as well as plants suffer.

EVOLUTION OF NEW CROPS/VARITIES
 Domestication is a good model for the study of evolutionary
processes because of the recent evolution of crop species
(<12,000 years ago), the key role of selection in their origins,
and good archaeological and historical data on their spread and
diversification. Recent studies, such as quantitative trait locus
mapping, genome-wide association studies and whole-genome
resequencing studies, have identified genes that are associated
with the initial domestication and subsequent diversification of
crops. Together, these studies reveal the functions of genes that
are involved in the evolution of crops that are under
domestication, the types of mutations that occur during this
process and the parallelism of mutations that occur in the same
pathways and proteins, as well as the selective forces that are
acting on these mutations and that are associated with
geographical adaptation of crop species.

EVOLUTION OF CROPS
 A divergent process which increases genetic diversity and leads
to change in allelic frequencies in a population is known as
evolution. In other words, a process which leads to significant
deviation in the characteristic features of existing individuals as
compared to their pre-existing individuals is termed evolution.
 Evolution –Natural & Man made. In case of natural evolution,
natural selection operates, while in man-made evolution human
selection operates. Thus, both natural and human selections
play significant role in the process of evolution. Plant breeding
is considered as current phase of crop evolution. Changes
which are brought out as a result of evolution are measured in
terms of morphological, anatomical, embryological,
physiological, biochemical and genetic modifications in the
present forms of individuals as compared with their past forms.

FACTORS OF EVOLUTION
 (1) Polyploidy,
 (2) Introgression, and
 (3) Mutations have played significant role in the evolution of
various crop plants.
 These three factors aid in the process of evolution by way of
inducing additional genetic variability, which is a basic
requirement for selection to operate.
 Polyploidy:
 Polyploidy refers to numerical change in the genome (A basic
set of chromosomes)-Auto polyploidy & Allopolyploids.
Allopolyploid bears strong significance as per as the speciation
is concerned as it results from doubling of chromosomes of
interspecific hybrid.

AUTOPOLYPLOIDS
 This is also known as simple polyploidy or single species
polyploidy, because the increase in chromosome number
relates to the same species. This type of polyploidy can occur
in nature as well as can be induced by colchicine treatment.
Increase in chromosome from diploid to tetraploid state leads
to increase in vigour and size of flowers and fruits over diploid
forms. However, polyploid plants exhibit slow growth rate and
reduced fertility due to chromosomal imbalance.
Autopolyploidy has been used in crops like banana, apples,
sugarbeet, watermelon, potato, oranges, tulips, etc. The
commercial banana is autotriploid (3n), which has seedless and
larger fruits than diploid forms. Some varieties of apples in
USA are triploids, which are propagated asexually by
budding and grafting. Triploid varieties of sugarbeet
have higher sugar content than diploids Triploid
watermelons.

INTROGRESSION
 Incorporation of gene of one species into the genetic
background of another species by means of interspecific
hybridization and backcrossing is known as introgression
(Anderson, 1949). The interspecific hybrid backcrosses in
nature with one of the parental species.
 As a result of introgression, genes from two divergent species
are combined. A true breeding recombinant form favored by
natural selection may give rise to a new species. Introgressive
hybridization between primitive maize and wild grass
Tripsacum is considered to be responsible for the evolution of
modern forms of maize.

MUTATIONS
 Mutations are important sources of creating variability in a
genetic population. Mutations can occur in nature as well as
can be induced by the use of physical or chemical mutagenic
agents. In hexaploid wheat, a natural mutation is responsible
for homologous pairing. Spontaneous mutations have played
significant role in the evolution of crop plants. Spontaneous
mutations can be used either as a cultivar or as a parent in the
hybridization programme. Induced mutations have played key
role in improving yield, quality, earliness, adaptation, and
disease and insect resistance in various crop plants.
 The bread wheat is hexaploid, combining diploid chromosome
complements from three different species. In nature, hexaploid
bread wheat behaves as diploid [n = 21 and 2n = 42]. It has
been found that hexaploid wheat has acquired this property of
diploid pairing from a mutation on chromosome number 5B,
which inhibits pairing between homologous chromosomes
(chromosomes of different genomes).

DIFFERENT TYPES OF CROP EVOLUTION
 The genetic evolution of some important field crops such as
wheat, cotton, tobacco, Brassica, potato, maize and rice is
briefly described below:
 The tetraploid species developed as an amphidiploids between
two diploid species, and hexaploid species originated from a
cross between tetraploid and diploid species. It is believed that
tetraploid species Triticum turgidum evolved as an
amphidiploids between Triticum monococcum (AA) and an
unknown species (now probably extinct) with BB genome. The
hexaploid bread wheat originated as an amphidiploids between
Triticum turgidum (AABB) and T. tauschii (DD). The overall
process can be represented as follows.

ALLOPOLYPLOIDS
 This is also known as hybrid polyploidy or bispecies or
multispecies polyploidy depending upon the species involved.
Such polyploidy is obtained by doubling of chromosome
number by colchicines treatment. Allopolyploid has been more
instrumental in evolution of crop plants, because 50% of the
crop plants are allopolyploids.
 Hybrid polyploidy has played significant role in the evolution
of crops like wheat, tobacco, cotton, Brassica, oat, etc.
Examples of artificially produced allopolyploids include
triticale, strawberry and loganberry.
 Triticale is a man-made new cereal (between wheat and rye),
which combines high yield of wheat and disease and drought
resistance of rye.

GERMPLASM & IMPORTANCE
 Germplasm contains the information for a species' genetic
makeup, a valuable natural resource of plant diversity.
Agriculture benefits from uniformity among crop plants within
a variety, which ensures consistent yields and make
management easier. Germplasm in a broad way can be
defined as the hereditary material i.e. total content of
genes which is inherited by the off springs through
germ cells. Germplasm serves as the raw material for
the breeder to produce various crops. Therefore,
conservation of germplasm has importance in all
breeding programmes.In previous days, humans
gained the knowledge about the use of plants for food ,
shelter and many more, thus they started saving
selected seeds or vegetative propagules from one
season to the next one. The possibility of life on earth
is mainly due to the plants as it is

GERMPLASM & IMPORTANCE
 the crucial component of the ecosystem, thus its preservation is
our responsibility for the continuation of life. In other words, it
may be regarded as the conventional germplasm preservation
and management, which is highly precious in breeding
programmes. The main objective of germplasm conservation is
to preserve the genetic diversity of selected plants or genetic
stock for its utilization at any time in future.
 In recent years, the primitive and conventionally used
agricultural plants are being replaced by many new plant
species with desired and improved characteristics. It is very
crucial to conserve the endangered plants otherwise some of
the important genetic traits possessed by the primitive plants
may be lost. It has been estimated that up to 100,000 plants,
depicting more than one third of all the world’s plant species,
are currently threatened or face extinction in the wild.

PROSPECTS OF GERMPLASM
 As previously stated, Genetic resource is treated as
Germplasm and the germplasm are used extensively for
the following attributes:1. Varieties used in cultivation-
There are good sources of genes for quality yield
because they can be introduced into new geographical
region for the cultivation to add economic
gain,2.Breeding lines- In the different breeding
programmes, the different narrow genetic base with
valuable gene combinations are used and they can be
used for the wide scale breeding exercises.3.For special
genetic stocks-These lines are carrying chromosomal
aberrations , gene mutations etc and these will be set of
monosomic or bisomic lines to be induced artificially,
 Wild relatives and forms- These are valuable source of
genes for development of GMP through genetic
engineering programmes.

ACKNOWLEDGMENTS
 1. For images: Google
 2. Different web pages or free resources
 Different articles from different web sites
 Economic Botany- Bhabananda Baruah,
 Economic Botany- S.Chand & company
 Disclaimer: This PPT has been made and designed for
purely academic purpose without any financial gain and
can be access freely by the academic fraternity.

Vavilov's Centres of Origin and Crop Domestication

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