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

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: • 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 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 • 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 seeds

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: • The number of samples to be collected from each plant • 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 • 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: • Keeping storage material a life • 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

SOURCE OF VARIATION