Download source of variation

SOURCE OF VARIATION
Source of variation
Plant genetic resource
Hybridization by sexual means
Induced mutation
Chromosome manipulation (ploidization)
Somatic hybridization
Transformation
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
productivity
 It has inestimable value
Distribution of plant genetic
resource
 The genetic variability of cultivated plants is
not randomly distributed throughout the
world
 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
Chinese-Japanese region Soybean, Citrus, Litchi, Bamboo, Rami, Tea
Indochinese-Indonesian
region
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
region
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
varieties
Cultivars
They have been obtained by
professional plant breeder
They are characterized by high
productivity and high genetic
vulnerability
Landrace
 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
varieties
 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
Landrace
 These varieties are not adequately represented in
existing collection today, due to:
1. In many collections, more importance is given to pure
lines and selected materials
2. Many of the populations collected in the field have
been subject to selection before being store,
thereby decreasing their genetic variability
3. 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
populations
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
generation
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
Objective
To conserve sufficient diversity within each
species to ensure that its genetic potential
will be fully available for breeding work
Conservation system
1. In Situ
2. 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
seeds
Advantage
Drawback
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
halted
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
collected)
Ex situ conservation of genetic resource
 Collection
 Maintenance
 Multiplication
 Evaluation
 Exchange
Collection
To collect the maximum genetic diversity and, if
possible, to obtain samples that maintain the allelic
frequencies of the collected populations or
varieties
 The team should have adequate knowledge of botany,
ecology, population genetics, plant breeding and plant
pathology
 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
farming
 Team must have a good knowledge of the plant habit
and breeding system
Collection
 Base collection
Collections stored under long-term conditions
 Active collection
Collections stored under medium-term
conditions
 Working collection
Collections usually stored under short-term
conditions (breeder’s collection)
Sample
 A most important aspect of the collection of the
material, since a sample must be representative of
the population genetic variability
 The main decisions:
1. The number of samples to be collected from each
plant
2. The number and distribution of the plant to be
collected in each site
3. 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

1.
2.
3.
4.
Including:
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
value
Maintenance
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
diversity
 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
accessible
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
-18°C can maintain good viability for a century or
longer
 For medium-term storage, 5 % MC seed can be stored
below 15°C
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-bank
 In vitro technique in slow growth conditions under
minimum media, low temperature and low light
intensity
Multiplication
 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:
1. Keeping storage material a life
2. Meeting the demand
Important aspect of
multiplication
 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
frequencies
 It is extremely important to take advantage of the
process of rejuvenation or multiplication in order to
eliminate viral or other infectious diseases
Evaluation
 To able to be used with maximum efficacy, stored
materials must be evaluated
 Pre-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
germ-plasm include the process of pre-breeding
Descriptor
 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
Exchange
 It can be achieved with the consent and/or
agreement of the parties involve and often
require international cooperation and
agreement
 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
diseases
 In vitro techniques for transfer of germplasm are widely used for some crops