In this article we will discuss about the genetic resources in crop production.
Genetic resources are the raw materials which scientists use to alter plant performance, and with which they hope to achieve the dramatic increase in crop production that will be required in the decades ahead.
Another factor of concern when considering biodiversity has been the emphasis on increasing yields by large scale production of superior clones. An obvious consequence of crop uniformity and neglect of wild related species, which often contain many useful traits, is a narrow gene pool and resultant vulnerability.
Papaya (Carica papaya) is an excellent example of a crop that is extremely vulnerable, but which is economically important in many tropical countries. In some of these countries, for example The Philippines, many farmers are already struggling with a subsistence existence and so the loss incurred by the failure of a cash crop causes real hardship.
The crop is threatened worldwide by a number of serious diseases, including viruses, namely Papaya Ring spot Virus (PRSV-P), fungal diseases including Phytophthora root, stem and fruit rots, and mycoplasmas. PRSV-P has devastated crop production in many regions and may cause many landraces or useful genotypes to be lost completely.
Extensive conventional crop breeding has achieved significantly improved fruit size and flavour and has been responsible for large improvements in crop yields but has been unsuccessful in addressing the current disease threats. However, the wild Carica relatives contain a huge pool of useful genes and valuable natural resistances to major papaya diseases have been observed.
Carica cauliflora, C. quercifolia, C. pubescens and C. stipulata have resistance to PRSV-P; Phytophthora-resistance has been found in C. goudotiana; and C. parviflora appears resistant to two mycoplasma diseases in field plantings at Redlands Research Station in Southeast Queensland, Australia.
Although the focus in collecting germplasm has been placed on plant species that are valuable as food sources, the case of papaya illustrates the value of other genetic resources. Documentation of wild relatives, landraces and their useful characteristics and in-situ or ex-situ collection requires much time, effort and funds.
However, the final benefits may be substantial, particularly as useful traits, such as resistance to a particular disease, potentially can be transferred to more than one crop species by gene transfer technology. The importance of germplasm conservation is being increasingly realised and many collections already exist.
The report on the State of World’s Plant Genetic Resources records some of the difficulties being encountered, for example ‘much of the plant genetic resources held in ex-situ collections are insufficiently and/ or poorly documented’ and ‘globally, governments and donor agencies have made insufficient provisions for on-going maintenance costs of conservation infrastructure’ resulting in a ‘steady deterioration of many facilities and their ability to perform even basic conservation functions’, and, ‘a high percentage of accessions that are held in these banks are in need of regeneration’.
These and other problems led to the adoption of The Global Plan of Action at the fourth International Technical Conference on Plant Genetic Resources for Food and Agriculture in June 1996.
Any attempt to systematically conserve genetic material on a worldwide basis will of course necessitate extensive government cooperation and funding. The task at hand is a daunting one but is complicated by the prevailing attitude of many governments in western countries to agricultural research.
Although they are signatories to all relevant conventions there is a growing reluctance to fund agricultural research. As funds dry up, competition causes available funding to go to those research areas promising significant results in the short term. Germplasm storage is not offering spectacular short term outcomes and is motivated by the need to take responsibility for the long term.
All countries need to value and be responsible for the conservation of genetic diversity. It is a natural resource, the value of which is still to be fully appreciated as science continues to unravel the mysteries of plant function at a cellular level and employ them to meet the constant stream of new and on-going pressures and difficulties facing crop production.
There is an urgent need to increase research into technologies that facilitate conservation of plant genetic resources. This is consistent with The Global Plan of Action.
Since the 1970’s there has been a conscientious effort to collect germplasm. In 1995, Tao and Anishetty reported that worldwide more than 4 million accessions of crop plants and their relatives were stored in gene banks and that there were 256 gene banks with long-term storage facilities and 1227 institutions with ex-situ collections.
However, these statistics are rendered less impressive by two considerations. Firstly, 40% of these accessions are cereals (wheat represents 14%). No consistent effort has been applied to the collection of other major crops, while minor crops including fruit crops, have been largely neglected. Secondly, more than 90% of the accessions are stored as seed.
As a consequence, vegetative propagated species and species with recalcitrant seeds are greatly underrepresented. In addition, if we are to preserve diversity, collections must also include wild relatives of crop species.
As gene transfer techniques overcome the incompatibility between species, there is also a need to be mindful that non-crop species may also represent a valuable source of useful genes such as disease and insect resistance.
Although seed storage has been the conventional method of conserving germplasm, pollen storage and field collections have also been employed. Scientific advances in the field of cell and tissue culture systems have made available, as alternatives, conservation in vitro in either slow growth systems or cryopreservation.
More recently, developments in molecular biology offer the future prospect of DNA storage as libraries of either DNA sequence information or of DNA constructs. As reported in the State of the World’s Plant Genetic Resources, one of the major concerns with germplasm storage is the maintenance of collections.
Stored germplasm requires careful characterisation as well as periodic regeneration to ensure viability. Techniques resulting from biotechnology offer improvements in this area. Molecular marker techniques enable characterisation at the DNA level, and an advantage of in vitro conservation is that viability is easily assessed visually.
As regular regeneration, usually annually, is essential, it is less likely to be overlooked. A major effort is still required in the evaluation and conservation of tropical and subtropical fruit species.
The development and maintenance of germplasm banks is of limited usefulness if the genetic material is not distributed and used worldwide to develop new and improved varieties of food plants. Hence The Global Plan of Action promoted the development of networks for the effective exchange and utilisation of germplasm.
It states that ‘networks are important platforms for scientific exchange, information sharing, technology transfer, research collaboration, and for the determination and sharing of responsibilities for such activities as collecting, conservation, distribution, evaluation and genetic enhancement’.
FAO has supported and collaborated in the development of networks in the 1990’s. Networks have been established on both a crop (mushroom, cactus pear, olive, citrus, nut tree) and regional basis.
The innovative aspect of the newly launched networks is the promotion of a coordinated approach to identifying, evaluating and conserving the genetic variability of selected crop species, with the aim of its utilisation for the improvement of cultivars and their adaptation to farmer’s needs’.
There exists the potential to strengthen existing networks, develop new networks and to coordinate these regional and crop-based networks into an effective global system.
The chief aims of The Global Plan of Action are the conservation and sustainable use of genetic resources, by developing more effective conservation strategies at both the national and international level. A major advantage of crop-based networks is that they can facilitate linkages between conservation and sustainable utilisation of crop genetic resources.
A number of factors highlight the importance of a global approach. Plant Genetic Resources (PGR) is a common concern of humanity and all nations are both donors and users of PGR. The effective use of a wide range of PGR in all countries is an incentive to ensure their conservation and maintenance.
Thus the international community as a whole has both an interest in and a responsibility to conserve PGR and this is the basis for an effective integrated and rational Global Plan of Action. A related development which emphasises the need for a global approach is the proposed World Information and Early Warning System on Plant Genetic Resources (WIEWS).
The technical meeting on the methodology of WIEWS recommended the establishment of a global network, on a voluntary basis, under the auspices of FAO. WIEWS would provide a vehicle to register cases of genetic erosion both in in situ populations and ex situ collections.
However, it would require an accurate information base on the current status of PGR including crop species, local varieties and wild relatives. The Global Network would provide ‘timely and precise information on PGR conservation and utilisation’ contribute to the implementation and updating of The Global Plan of Action, provide an information flow between countries and develop an effective early warning system.