12 déc. 2012 (il y a 9 années et 1 mois)

365 vue(s)


Source of variation

Plant genetic resource

Hybridization by sexual means

Induced mutation

Chromosome manipulation (ploidization)

Somatic hybridization


Plant genetic resources

Basic for agricultural development

A reservoir of genetic adaptability that acts
as a buffer against environmental change

Its erosion threatens world food security

It is limited and perishable natural resource

It provides raw materials to produce new and
better plant varieties

It is irreplaceable source of important
characters such as resistance to disease and

It has inestimable value

Distribution of plant genetic

The genetic variability of cultivated plants is
not randomly distributed throughout the

Zhukovsky (1965) identified 12 megagene
centers of crop
plant diversity and a number
of microgene center of wild growing species
related to crop plants

Zeven & Zukovsky (1975) listed the species
for different megagene center and the range
and extent of distribution of its diversity

Regions of diversity

Japanese region

Soybean, Citrus, Litchi, Bamboo, Rami, Tea


Rice, Mango, Banana, Rambutan, Durian, Bread
fruit, Bamboo, Sago palm, Ginger, Coconut

Australian region

Eucalyptus, Acacia, Macademia

Hindustani region

Rice, Eggplant, Okra, cucumber, Banana, Mango

Central Asian region

Onion, Radish, Carrot, Sesame

Near Eastern region

Pear, Apple, Pea, Sesame

Mediterranean region

Durum, olive, Radish

African region

Durum, Cotton, kenaf, coffee

European Siberian

Peach, Chicory

South American region

Potato, Tobacco, Tomato, Groundnut, cassava,
cacao, rubber

Central American and
Mexican region

Maize, Chili, Cotton

North American region

Sunflower, plum, strawberry

Classification of plant
genetic resource

Cultivated species

1. Commercial varieties

2. Landraces or traditional local varieties

3. Breeding lines

4. Special genetic stocks

wild species

1. For direct use

2. For Indirect use

3. Potentially utilizable

Commercial varieties

Standardized and commercialized


They have been obtained by
professional plant breeder

They are characterized by high
productivity and high genetic


They are primitive varieties or cultivars which have
evolved over centuries or even millennia and have
been influenced decisively by migration and both
natural and artificial selection

There is a large diversity between and within these

They are adapted to survive in unfavorable condition,
have low but stable levels of productivity and are
characteristic of subsistence agriculture

Greatest attention, due to:

1. the abundance of potentially useful genetic variation
they contain in already co
adapted gene complexes

2. The speed with which they are disappearing when
replaced by commercial varieties


These varieties are not adequately represented in
existing collection today, due to:

In many collections, more importance is given to pure
lines and selected materials

Many of the populations collected in the field have
been subject to selection before being store,
thereby decreasing their genetic variability

Most collections have been maintained traditionally
through periodic multiplications in small adjoining
fields with a consequent genetic erosion due to
hybridization, natural selection and the genetic drift
characteristic of small populations

Breeding lines

They are materials obtained by plant breeder as
intermediate product

They have a narrow genetics base because they have
originated from a small number of varieties or

Special genetic stock

Stocks include other genetic combination, such as:

1. Mutant

2. Inter
specific hybridization product

3. Somatic hybridization product

4. Transgenic product

Direct use

Genetic erosion doesn’t occur by chance, but
selectively, against the most valuable material

People often select and consume the plant
possessing the most desired characteristics

Such consumption frequently involves the
destruction of either the seed or the plants
before seeds have been produced, setting of
negative selection that ends with the
elimination of those characters in a few

Indirect use

There are wild species related to cultivated species
possessing beneficial characters that can be
transferred to cultivar relatives through crossing,
somatic hybridization even genetic engineering

In vegetative reproduced species, the wild relatives
can sometimes be used as rootstock for grafting.
Through this system, the crop can be extended to
marginal areas and also possible to prevent certain
infectious disease

Potentially utilizable

These species which are not used today have
characteristics or composition which make their use
in the future probably

This includes many wild species for which analysis in
pharmaceutical laboratories has revealed contents of
certain medicinal substances which are higher than in
species traditionally used to obtain these product

Conservation of plant
genetic resource


To conserve sufficient diversity within each
species to ensure that its genetic potential
will be fully available for breeding work

Conservation system

In Situ

Ex Situ

These two system should be considered complementary,
not antagonistic

In situ conservation

It consists in the legal protection of the area and
habitat in which the species grows

This is the preferred technique for wild plant

The advantage is the evolutionary dynamics of the
species are maintained

The drawback is the cost, and the social and political
difficulties which occasionally arise

Ex situ conservation

It implies the collection of representative samples of
the genetic variability of a population/cultivar, and
their maintenance in germ
plasm banks or botanical
gardens as seeds, shoots, in vitro culture, plants

It is mainly used for cultivated plants multiplied by



1. The control materials in a small
space under intensive care

1. The germ
plasm cease to evolve,
and the natural processes of
selection and continuous
adaptation to local habitat are

2. The materials is easily access to
plant breeder

2. Genetic drift (random loss of
diversity due to the fact that the
samples collected and multiplied
are necessarily very small)

3. Selection pressure (the material
is usually multiplied in
phytoecogeographical area
different from those where it was

Ex situ conservation of genetic resource







The team should have adequate knowledge of botany,
ecology, population genetics, plant breeding and plant

The team must be familiar with species to be
collected and to have a good knowledge of the
country or region where the expedition is conducted
including socio
ecological and cultural aspects of the

Team must have a good knowledge of the plant habit
and breeding system

To collect the maximum genetic diversity and, if
possible, to obtain samples that maintain the allelic
frequencies of the collected populations or


Base collection

Collections stored under long
term conditions

Active collection

Collections stored under medium

Working collection

Collections usually stored under short
conditions (breeder’s collection)


A most important aspect of the collection of the
material, since a sample must be representative of
the population genetic variability

The main decisions:

The number of samples to be collected from each

The number and distribution of the plant to be
collected in each site

The number and distribution of the sites within a
given area where collecting will be carried out

The answer are not always the same and will depend
on the specific circumstance of each case

Collection’s usefulness

A very relative term

It may vary according to the collectors

Plant breeders will look for useful agronomic
characteristics (selective sampling)

Population geneticist may try to collect randomly
(random sampling)

Field Passport

A very important data


Climatic characteristic

Soil characteristic

Type of vegetation

Type of integrated pest

The information provided by farmers and field
workers living in collecting area will be of unique


In the form of
core collection

Development of a small group accessions

It represents collection with a minimum of
repetitiveness in the genetic diversity of crop
species and its wild relative

It is believed to contain most of known genetic

It can be used as a point of entry to the available
collections of a crop

It should not replace existing collections

It is a way of making existing collections more

Maintenance System

Dependent upon propagation system:

seed propagated species

vegetative propagated species

Seed propagated species

1. Its storage longevity can be induced by decreasing its storage
temperature and humidity

2. It is affected by seed type

a. Orthodox

b. Sub orthodox

c. Recalcitrant

Safe long
term of orthodox seeds

It requires careful control of the environment in
which the seed are kept

Seed moisture content is the most important factors
affecting seed storage life

Seed stored under moisture proof container at about
C can maintain good viability for a century or

For medium
term storage, 5 % MC seed can be stored
below 15

Recalcitrant seeds

The period of viability varies between 2 weeks and
several months

There are some major economic value i.e. cocoa,
coconut, rubber

Vegetative propagated species

Field growing collections as in arboretum, a field gene
bank, a botanical garden or a nature reserve

Controlled humidity and temperature conditions for
cuttings, bulbs and tubers. It is only practical for
short and medium term or used in conjunction with a
field gene

In vitro technique in slow growth conditions under
minimum media, low temperature and low light


Problem of germ
plasm collection

loss of the
germination capacity of stored materials

It varies according to species and variety

Germination test is necessary

The important use of multiplication:

Keeping storage material a life

Meeting the demand

Important aspect of

Avoiding genetic contamination by taking into account
the reproductive characteristics of species,
particularly the out
crossing rate

The site should have ecological characteristics similar
to those where the materials was collected, in order
to prevent selection that can change the allelic

It is extremely important to take advantage of the
process of rejuvenation or multiplication in order to
eliminate viral or other infectious diseases


To able to be used with maximum efficacy, stored
materials must be evaluated

breeding (Other term)

It can deal with one or several possible aspects i.e.
agronomic, pathological, morphological, biochemical,
cytological and other things

All data can help toward detecting duplications and
differences among the conserved samples

Development breeding (Germplasm enhancement

Program which aim to facilitate the utilization of plant
plasm include the process of pre


Characters considered important or useful in the
description of a population

Differ according to species as to whether they have
been selected by plant breeders, botanists,
geneticists or experts in other disciplines

The degree of usefulness depends on the objectives

There is a tendency toward accepting compromise
solutions through selection of a minimum number of
universally accepted descriptor that can facilitate
the exchange of information and material (protein
and molecular marker as a fingerprint)

A good documentation system is the key to
the effective utilization of the materials
deposited in a germ
plasm bank


It can be achieved with the consent and/or
agreement of the parties involve and often
require international cooperation and

The exchange of material also requires
adequate inspection and testing services as
well as quarantine facilities that can reduce
to a minimum the risks of spreading pests and

In vitro techniques for transfer of germ
plasm are widely used for some crops