SOURCE OF VARIATION

Source of variation

Plant genetic resourceHybridization by sexual meansInduced mutationChromosome manipulation

(ploidization)Somatic hybridizationTransformation

Plant genetic resourcesBasic for agricultural developmentA 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 diversityChinese-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

CultivarsThey have been obtained by

professional plant breederThey 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 materials2. 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. Mutant2. Inter-specific hybridization product3. Somatic hybridization product4. 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 Drawback1. The control materials in a small

space under intensive care1. 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

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

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

or varieties

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 plant2. The number and distribution of the plant to be

collected in each site3. 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

Including:1. Climatic characteristic2. Soil characteristic3. Type of vegetation4. 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 species1. 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 germ-plasm are widely used for some crops