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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
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)
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
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