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Centers of origin and diversity of crop plants
Crop genetic diversity refers to the variety of genes and genotypes found in a
particular crop species. Genetic diversity is essential to develop improved cultivars with
broad genetic base and wide adaptability. Moreover, existence of genetic diversity is also
essential to meet current and future breeding requirements. If a crop species has large
number of genetic variants it is said to be genetically diverse. Genetic diversity provides
broad genetic base to the population.
N.I Vavilov (1926, 1951) a Russian geneticist and plant breeder, was the pioneer
man who realized the significance of genetic diversity for crop improvement. Vavilov
and his colleagues visited several countries and collected cultivated plants and their wild
relatives for use in the Russian breeding programme to develop varieties for various
agroclimatic conditions of USSR.
Based on his studies of global exploration and
collection, Vavilov proposed eight main centres of diversity and three subsidiary centres
of diversity.
Centre of diversity refers to a place, region or area where maximum variability
and diversity of crop plants is observed. The centres of diversity were also considered as
centres of origin of crop plants. The various centres of diversity as proposed by N.I
Vavilov include:
(1) Chinese Centre,
(2) India Centre,
(2a) Indo-Malayan Centre,
(3) Central Asiatic Centre,
(4) The Asia Minor Centre
(5) Mediterranean Centre,
(6) Abyssinian Centre
(7) South Mexican and Central American Centre,
(8) South American Centre
(8a) Chilean Centre, and
(8b) Brazilian- Paraguayan centre
All these centres are also known as Vavilovian centers of diversity
Table .7 Vavilovian centres of diversity of crop plants (after Vavilov, 1951)
Name of centre
1. Chinese Centre:
It
consists
of
the
mountainous regions of
central and western China
and the neighbouring low
lands. It is the largest and
oldest independent center.
2. Indian Centre: This
includes
Burma,
Assam,
Malaya, Java Borneo,Sumatra
and Philippines, but excludes
North West India, Punjab and
North
Western
Frontier
Provinces.
2(a) Indo-Malayan Centre
3. Central Asiatic Centre: It
includes North West India, all
of Afghanistan, the Soviet
Republics of Tadjikistan and
Tian Shan. It is also known as
the Afghanistan center of
origin.
4. Asia Minor Centre: This is
also known as the Near East
or the Persian Centre of
Origin. It includes the interior
of Asia Minor, the whole of
Transacaucasia, Iran and
Highlands of Turkmenistan.
Main crops for which genetic diversity is found
Naked oat (SC), Soybean, Adzuki bean, Common bean
(SC) Small Bamboo, Leaf Mustard (SC), Apricot, Peas,
Orange, Sesame (SC), China tea, etc.
Rice, Chick pea, Moth Bean, Rice bean, Horse gram,
Brinjal, Cucumber, Tree Cotton, Jute, Pepper, African
Millet, Indigo, etc.
Banana, Coconut, Yam and Pomelo
Bread wheat, Club wheat, Shot wheat, Rye (SC) Lentil,
Chickpea, Sesame, Flax, Safflower, Carrot, Radish,
Apple, Pear and Walnut
Einkorn wheat, Durum wheat, Poulard wheat, Bread
wheat, Two Rowed barley, Rye, Red oat, Chickpea
(SC), lentil, pea (SC), Flex, Almond, Pomegranate,
Pista, Apricot and Grape
5. Mediterranean Centre
6. Abyssinian Centre: It
includes Ethiopia and hill
country of Eritrea.
7. South Mexican and Central
American Centre : This
includes South Mexico and
Central America. It is also
referred to as the Mexican
Centre of Origin.
8. South American Centre:
This center includes the high
mountainous regions of Peru,
Bolivia, Ecuador, Colombia,
parts of Chile, and Brazil and
whole of Peraguay.
8(a) Chilean Centre
8(b)
Brazilian
Paraguan
Centre
Durum wheat, Husked oats, Cabbage, Olive, Broad
beans and Lettuce.
Durm wheat, Poulard wheat, Emmer wheat, Barley,
Chickpea, Lentil, Pea, Flax, Sesame, Castor bean,
African millet and Coffee
Maize, Common bean, Upland cotton, Pumpkin, Gourd,
Squash, Sisal hemp and Pepper
Potao, Sweet potato, Lima bean, Tomato, Papaya,
Tobacco and Sea Island cotton.
Potato
Peanut, Rubber Tree, Cocoa (SC), Pineapple, etc.
SC = Secondary centre
Vavilov could not adequately cover Africa, Moreover, Australia was not at all
covered. These two continents have tremendous wealth of crop genetic diversity of
several crop plants. The main difference between centre of origin and centre of diversity
is that centre of origin of a crop species is generally confined to one place, whereas the
diversity of a crop may be found at more than one place.
It is clear from the various centres of diversity that some crop plants have more
than one centre of diversity. Moreover, centres of diversity are of two types, viz., (1)
primary centres of diversity, and (2) secondary centres of diversity. They are briefly
discussed below.
Primary centres of diversity
Primary centres are regions of vast genetic diversity of crop plants. These are
original homes of the crop plants which are generally uncultivated areas like, mountains,
hills, river valleys, forests, etc. Main features of these centres are given below.
1. They have wide genetic diversity
2. Have large number of dominant genes
3. Mostly have wild characters
4. Exhibit less crossing over
5. Natural selection operates
Secondary centres of diversity
Vavilov suggested that valuable forms of crop plants are found far away from
their primary area of origin which he called secondary centres of origin or diversity.
These are generally the cultivated areas and have following main features.
1. Have lesser genetic diversity than primary centres
2. Have large number of recessive genes
3. Mostly have desirable characters
4. Exhibit more crossing over
5. Both natural and artificial selections operate
Microcentres
In some cases, small areas within the centres of diversity exhibit tremendous
genetic diversity of some crop plants. These areas are referred to as microcentres.
Microcentres are important sources for collecting valuable plant forms and also for the
study of evolution of cultivated species. The main features of micro centres are given
below.
1. They represent small areas within the centres of diversity
2. Exhibit tremendous genetic diversity
3. The rate of natural evolution is faster than larger areas
4. They are important sites for the study of crop evolution
Vavilov also developed the concept of parallel series of variation or Law of
homologous series of variation. This concept states that a particular variation observed
in a crop species is also expected to be available in its another related species. For
instance, if we get dwarf collections in one crop species the same may be found in
another related species also.