Plant Genetic Resources And Conservation

Plant Genetic Resources and Conservation

INTRODUCTION Global concern about loss of valuable genetic resources prompted international action. The reasons for this loss are many and include deforestation, developmental activities such as hydroelectric projects, road laying, urbanization and changes in agricultural practices, and finally modern agriculture and introduction of new and uniform varieties. Programs for conservation of plant genetic resources for food security and agriculture were thus initiated and genebanks established in many countries. The main objective was to collect and maintain the genetic diversity in order to ensure its continued availability to meet the needs of different users. The concept of germplasm conservation demands that collection methods initially capture maximum variation and subsequently, conservation and regeneration techniques minimize losses through time. To this effect, plant genetic resources (PGR) conservation activities comprise of collecting, conservation and management, identification of potentially valuable material by characterization, and evaluation for subsequent use. Advances in biotechnology, especially in the area of in vitro culture techniques and molecular biology provide some important tools for improved conservation and management of plant genetic resources. Types of Germplasm Advanced (or elite) germplasm includes (a) "cultivars," or cultivated varieties, which are suitable for planting by farmers, either recently developed cultivars or "obsolete" cultivars that are no longer grown, and (b) advanced breeding material that breeders combine to produce new cultivars (sometimes referred to as "breeding materials").

Improved germplasm is any plant material containing one or more traits of interest that have been incorporated by scientific selection or planned crossing. Landraces are varieties of crops improved by farmers over many generations without the use of modern breeding techniques. Within a modern breeding program, landraces are sometimes used for resistance traits, and extensive efforts are generally required before their genes can be used in a final variety.

Wild or weedy relatives are plants that share a common ancestry with a crop species but have not been domesticated. These plants can serve as another source of resistance traits, but these traits can be very difficult to incorporate in final varieties.

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Plant Genetic Resources and Conservation

Genetic stocks are mutants or other germplasm with genetic abnormalities that may be used by plant breeders for specific purposes. Genetic stocks are often used for highly sophisticated breeding and basic research.

Why Is Germplasm Important? The relationship between access to genetic resources and agricultural production is often overlooked. The plant breeding process is complex and continual, and diverse genetic resources are a critical input. Advances in yield potential, pest resistance, quality, and other desirable traits in modern varieties have resulted from professional breeders crossing diverse parental genetic material. Farmers who rely on their crop output for seed or consumption and professional plant breeders both depend on crop genetic resources. In turn, the efforts of farmers and plant breeders can generate new genetic resources. About 10,000 years ago, people in parts of Asia, the Near East, and Mesoamerica (modern-day Mexico and Central America) began to deliberately cultivate specific species. Over the generations, farmers selected and improved particular crops. In many parts of the world, this process continues today with farmerdeveloped varieties known as landraces. Landraces have been adapted to specific environments, and the areas in which they grow host many diverse varieties. GERMPLASM COLLECTING AND TECHNIQUE USED FOR PREPARATION AND COLLECTION Collecting involves gathering samples of a species from populations in the field or natural habitats for conservation and subsequent use. Collecting may be easy in species producing small botanic seeds in abundance. However, it becomes problematic when seeds are unavailable or non-viable due to (a) damage of plants by grazing or diseases (b) large and fleshy seeds that are difficult to transport; or (c) where samples are not likely to remain viable during transportation due to remoteness of the collecting site from the genebank.

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Plant Genetic Resources and Conservation

Advances in biotechnology provide useful solutions for collecting such problem species: Plant

Difficulty

coconut Cocos nucifera

large size of the seeds

cacao Theobroma cocoa

rapid deterioration of samples during transit as the seeds do not withstand desiccation.

Solution in vitro techniques have been developed that allow collecting of the relatively small zygotic embryos in the field and transporting them back in sterile conditions to the laboratory to inoculate and germinate them on a culture medium. simple in vitro method that involved collecting shoot nodal cuttings, followed by sterilization and inoculation of tissue into prepared culture vials containing semi-solid medium.

In vitro collecting methods were also developed for a range of other species including oil palm, forage grasses, banana, coffee, grape, Prunus and Citrus spp. CONSERVATION – MODERN BIOTECHNOLOGY METHODS There are two approaches for conservation of plant genetic resources, namely in situ and ex situ. In situ conservation involves maintaining genetic resources in the natural habitats where they occur, whether as wild and uncultivated plant communities or crop cultivars in farmers’ fields as components of the traditional agricultural systems. Ex situ conservation on the other hand, involves conservation outside the native habitat and is generally used to safeguard populations in danger of destruction, replacement or deterioration. Approaches to ex situ conservation include methods like seed storage, field genebanks and botanical gardens.

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Plant Genetic Resources and Conservation

Conventional ex situ conservation seed storage Methods Problems Solution propagation • most convenient for • tropical and sub-tropical clonal long-term conservation. tree produce recalcitrant preferred to conserve elite seeds that quickly lose genotypes. • involves desiccation of viability and do not seeds to low moisture survive desiccation. contents and storage at low temperatures. • also a number of other important crop species that are sterile or do not easily produce seeds, or seed is highly heterozygous field genebanks Methods Problems provide easy access to run the risk of destruction by conserved material for use natural calamities, pests and diseases

Examples banana, sweet potato, sugarcane, cassava, yam, potato, and taro.

Biotechnology contributed significantly by providing complementary in vitro conservation options through tissue culture techniques. In vitro conservation also offers other distinct advantages. For example, the material can be maintained in a pathogen-tested state, thereby facilitating safer distribution. Further, the cultures are not subjected to environmental disturbances. In general, they fall under two categories: (i) slow growth procedures and (ii) cryopreservation. Slow growth allow clonal plant material to be held for 1-15 years under tissue culture conditions with periodic sub-culturing, depending on species Methods • a low temperature with low light intensity is used to limit growth. • temperatures in the range of 0-5ºC are employed with cold tolerant species, but for tropical species, temperatures between 15º and 20ºC are used. • limit growth by modifying the culture medium, mainly by reducing the sugar and/or mineral elements concentration and reduction of oxygen level available to cultures. Protocols • Protocols for clonal multiplication are well established for several species. • Generally, organized cultures such as shoots are used for slow growth storage since undifferentiated tissues such as callus are more vulnerable to somaclonal variation. Although slow growth procedures have been developed for a wide range of species, they are routinely used for conservation of genetic resources of only a few species including Musa spp., potato, sweet potato, cassava, yam, Allium spp. and temperate tree species.

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Plant Genetic Resources and Conservation

Cryopreservation storage of plant material at ultra-low temperatures in liquid nitrogen (-196°C) • At -196°C, cell division and metabolic activities remain suspended and the material can be stored without changes for long periods of time. • only available method for long-term conservation of vegetatively propagated plant germplasm. Choice of materials cells, protoplasts, shoot apices, somatic embryos, seed or excised zygotic embryos Advantages • limited space. • protects material from contamination. • involves very little maintenance. • cost-effective. Technique • older classical techniques based on freeze-induced dehydration of cells. • newer techniques based on vitrification Classical technique • tissues are cooled slowly at a controlled rate (usually 0.1-4°C/min) down to about – 40ºC, followed by rapid immersion of samples in liquid nitrogen using a programmable freezing apparatus. • cryoprotectants are added to the freezing mixtures to maintain membrane integrity and increase osmotic potential of the external medium. • have been successfully applied to undifferentiated culture systems such as cell suspensions and calluses • • •

Vitrification involve removal of most or all freezable water by physical or osmotic dehydration of explants, followed by ultra-rapid freezing which results in vitrification of intracellular solutes. more appropriate for complex organs like embryos and shoot apices; they are also less complex and do not require a programmable freezer, hence are suited for use in any laboratory with basic facilities for tissue culture. there are seven vitrification-based procedures in use for cryopreservation: (1) encapsulation-dehydration, (2) vitrification, (3) encapsulation-vitrification, (4) desiccation, (5) pregrowth, (6) pregrowth desiccation, and (7) droplet freezing.

In general, cryopreservation is well established for vegetatively propagated species. However, it is much less advanced for recalcitrant seed species due to some of their characteristics, including their very high sensitivity to desiccation, structural complexity and heterogeneity in terms of developmental stage and water content at maturity. The new cryopreservation techniques have been successfully applied for more than 80 species (some examples: rice, wheat, barley, mustard and coconut) and they are under development or vigorous testing for several other species. However, examples of their routine use for longterm conservation are still limited only to oil palm and potato. CHARACTERIZATION OF DIVERSITY The ability to identify genetic variation is indispensable to effective management and use of genetic resources.

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Plant Genetic Resources and Conservation

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Traditional method measuring variation in phenotypic traits such as flower colour, growth habit or quantitative agronomic traits like yield potential, stress tolerance etc. has certain limitations: genetic information provided by morphological characters is often limited and expression of quantitative traits is subjected to strong environmental influence. Biochemical method based on seed protein and enzyme electrophoresis; introduced in 1960s. useful in analysis of genetic diversity as they reveal differences between seed storage proteins or enzymes encoded by different alleles at one or more gene loci. eliminates the environmental influence. limited due to their inability to detect low levels of variation. Molecular method used as complementary strategies to traditional approaches; increasingly playing an important role in conservation and use of plant genetic resources. can be performed at any growth stage using any plant part and it requires only small amounts of material. methods differ with respect to technical requirements, level of polymorphism detected, reproducibility and cost. generally based on the use of restriction enzymes that recognize and cut specific short sequences of DNA (e.g., Restriction Fragment Length Polymorphism, RFLP) or polymerase chain reaction (PCR), which involves amplification of target DNA sequences using short oligonucleotide primers. Specific areas in which molecular marker techniques have been used are: developing sampling strategies and identification of gaps in the collections to plan for future collecting and acquisition, and managing conserved germplasm – including identification of redundancies, development of core collections, fingerprinting, identification of genetic contamination and quantification of genetic drifts/shifts.

Nevertheless, it is difficult to compare the different techniques and determine which one is best and for what purpose because each method has its advantages and disadvantages. The appropriateness of individual marker systems also varies depending on the objective of study and the properties of the species. Sampling strategies Molecular markers have been applied to study genetic diversity from natural populations and formulate efficient sampling strategies to capture maximum variation for genetic resources conservation. For example, the substantially higher level of RFLP variation observed in self-incompatible, as compared with self-compatible species of Lycopersicon was used to recommend predominant sampling of self-incompatible species for germplasm acquisition. Studies of distribution of genetic diversity using AFLP markers in Sri Lankan coconut populations showed that emphasis should be placed on collecting relatively large numbers of plants from few populations since most of the diversity is within populations rather than between populations. Genetic variation within and between natural populations of Digitalis obscura was quantified using RAPDs and the results were used for optimizing sampling strategies for conservation of genetic resources of the species. Recommendations to focus on the sampling of marginal pawpaw (Asimina triloba) populations in future collection missions were derived from the genetic structure across natural distribution areas, established by RAPD analysis.

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Plant Genetic Resources and Conservation

Managing genetic resources Molecular techniques proved useful in a number of ways to improve the conservation and management of PGR. In particular, genetic diversity data provides information on gaps in terms of coverage in gene pools as well as redundancies, i.e., material with similar characteristics that wastes resources through increased cost of management. For example, RAPD analysis in Brassica oleracea revealed that 14 phenotypically uniform accessions could be reduced to 4 groups with minimal loss of genetic variation. Intraaccession variation was determined by AFLP markers in ex situ conserved barley, and results were used to evaluate the efficiency of splitting heterogeneous accessions into distinct lines in order to avoid the negative effects of selection and genetic drift during regeneration. Recent examples of use of molecular markers to identify redundancies in collections include perennial kales, wheat, grapevine, sorghum, cassava, flax, and barley. Molecular markers have been employed for fingerprinting, verification of accession identity and genetic contamination. For example, microsatellites were used to distinguish different cultivars of grapevine, and to compare landraces and develop unique DNA profiles of soybean genotypes. Variation within species has also been studied to explore geographic or ecological patterns of distribution of diversity in many different crops and their wild relatives that include wild bean (Phaseolus vulgaris), banana, mango, bambara groundnut, vetch, Cicer spp., sorghum, sweet potato, tea, and chicory. Molecular markers are being increasingly used to resolve problems of taxonomy and phylogenetic relationships, as a good knowledge of genomic homologies helps in devising suitable breeding strategies for appropriate conservation as well as transfer of genes from one species to another. In situ conservation Diversity studies using molecular markers have also assisted in developing in situ conservation strategies. The advent of molecular genetic markers made it easy to discriminate between wanted and unwanted agronomic genes in segregating populations. If linkages are established between a heritable agronomic trait and a genetic marker, markers can be used to identify the location of genes. Such linkages allow direct selection for the trait using marker assisted selection in a backcrossing programme. Molecular markers, which densely cover an entire crop genome, can be applied to develop a molecular map for a crop, which could be used to determine linkage between a specific molecular marker and a strongly heritable trait. This holds great promise for breeding programmes, as many traits are difficult to select for directly from breeding populations. CONCLUSION Biotechnology has made significant contributions to improved conservation and use of plant genetic resources. The rapid progress made in in vitro culture technology has helped in improving the conservation of genetic resources especially of problem species. Some of the most important contributions have been in the areas of in vitro collecting, slow growth and cryopreservation. Slow-growth techniques are in a more advanced state of development than cryopreservation techniques, which still require improvement before they can be used on a routine basis in a number of species. By facilitating better understanding of diversity, both in extent and structure, molecular marker techniques are proving extremely useful in identification of redundancies in collections, in testing accession stability and integrity, and in supporting the development of effective management strategies both for ex situ and in

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Plant Genetic Resources and Conservation

situ conservation. Molecular genetic studies are also being increasingly used to support improved use of plant genetic resources. The sequence data that are becoming available for increasing numbers of genes as a result of the rapid advances in DNA technology have stimulated the development of novel molecular technologies which allow the screening of germplasm for functional diversity and identify variation at an early developmental stage without the need for performing the time-consuming evaluation tests.

International Issues and Agreements Historically, plant genetic material was generally freely collected and shared. Today’s developing countries-with a wealth of biological diversity in situ (in the wild and on fields)were often the source of raw genetic material collected by public gene banks worldwide. Now, however, critics argue that unrestricted access to germplasm unaccompanied by benefit sharing results in an inequitable system of exchange. For example, freely shared crop traits from donor countries could be incorporated into varieties by researchers in developed countries and then sold back to donor country farmers by private seed companies. The lack of direct compensation is seen as giving donor countries little incentive to conserve genetic resources, some of which are now at risk of extinction. Proponents counter that a system of “free exchange” indirectly compensates lower income countries for donations of raw genetic materials in two ways. First, these countries have had free access to public gene banks, whose holdings include improved varieties. Second, many lower income countries are net importers of food, and consumers in those countries benefit from lower world food prices made possible by genetic improvements, regardless of where the improvements were made. Several international agreements have sought to further the preservation of genetic resources and to balance the sharing of benefits generated by their use. In 1983, the Commission on Plant Genetic Resources (now the Commission on Genetic Resources for Food and Agriculture) was established under the auspices of the Food and Agricultural Organization (FAO) of the United Nations. The Commission developed the International Undertaking, a nonbinding treaty to govern the exchange of genetic resources, but some developing and developed countries (including the U.S.) did not commit to its implementation. In 1992, the U.N. Convention on Biological Diversity (CBD) was established, with a focus on the preservation of biodiversity, especially those genetic resources with pharmaceutical and industrial rather than agricultural uses. In an attempt to ensure equitable returns to donor countries for the use of native resources (and to spur conservation), the CBD granted nations sovereign rights to genetic resources within their borders, which in practice meant both nonagricultural and agricultural germplasm. International agreements on intellectual property rights also have implications for genetic resource conservation. Stronger intellectual property rights provide incentives for private research and development (R&D) investment, and, in theory, also enhance incentives for conserving genetic resources. However, intellectual property law varies from country to country and may not cover unimproved germplasm and farmer-developed varieties. The World Trade Organization’s (WTO) agreement on Trade-Related Aspects of Intellectual Property Rights has provisions that can affect the exchange of germplasm. WTO member countries must commit to implementing a system protecting intellectual property for plant genetic resources, and noncompliance can result in sanctions.

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Plant Genetic Resources and Conservation

The New Treaty The new International Treaty on Plant Genetic Resources for Food and Agriculture was intended to bring the International Undertaking into conformity with the CBD. After lengthy negotiations, delegates from 116 countries adopted the text of the treaty in November 2001, with the American and Japanese delegates abstaining. The new treaty has several objectives. First, it mandates the conservation and sustainable use of plant genetic resources for food and agriculture. Second, it seeks fair and equitable sharing of benefits arising out of the use of these resources. Finally, it establishes a multilateral system to facilitate access to all crops listed in Annexes I and II of the treaty and to share the benefits derived from such facilitated access under the terms of a standard Material Transfer Agreement (MTA). The treaty specifies that the Governing Body at its first meeting will establish the terms of the standard MTA after the treaty enters into force. Much remains to be resolved. Application of intellectual property rights to plant genetic resources remains a contentious issue. Precisely how benefits will be shared has yet to be determined and is complicated by: (a) A lack of consensus regarding what “equitable” benefit sharing means (b) Disagreement over how to estimate the magnitude of benefits derived from use of shared Germplasm (c) Substantial variability in benefit estimates derived from similar assessment methods. Unlike the CBD, which provides for bilateral negotiations to establish the terms of access and benefit sharing for each specific exchange of materials, all germplasm exchanges under the multilateral system will be subject to the standard MTA. Monetary benefits will be paid to a fund established by the Governing Body. This fund will be used primarily to support farmers who conserve and sustainably use plant genetic resources for food and agriculture, especially such farmers in developing countries or in countries with economies in transition. The new treaty addresses the financing of germplasm conservation only in general terms, making this aspect of the treaty potentially difficult to implement. The overall impact of the treaty is also limited by its omission of soybeans, peanuts, and other major world crops from the list of 35 crops covered. Crops covered under the International Treaty on Plant Genetic Resources for Food and Agriculture Apple Breadfruit Pea Major aroids: includes Carrot Pearl millet taro, cocoyam, dasheen, Cassava Pigeon pea and tannia Chickpea Potato Brassica complex: Citrus Rice includes Coconut Rye cabbage, rapeseed, Cowpea Sorghum mustard, cress, Eggplant Strawberry rocket, radish, and turnip Faba bean /Vetch Sunflower Asparagus Finger millet Sweet potato Banana/Plantain Grass pea Triticale Barley Lentil Wheat Bean Maize (corn) Yam Beet Oat

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Plant Genetic Resources and Conservation

Despite the progress made, there remain many unresolved questions, the most important being that of determining the most appropriate molecular markers for the required understanding of the patterns of diversity in specific studies. While there is a pressing need to ensure that available technologies are made accessible to a wider range of users through improved training and other capacity building initiatives, the existing technologies are also expensive and given that most of the crop diversity is to be found in developing countries, the issue of resources assumes importance. Hence, there is real need to maximize synergy through appropriate collaboration between various national, sub-regional and international levels, including sharing burdens and responsibilities, in order to use these techniques for effective conservation and use of plant genetic resources.

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