| CCP: BA/TF 01/6
|
| CCP: BA/TF 01/6
|
COMMITTEE ON COMMODITY PROBLEMS |
INTERGOVERNMENTAL GROUP ON BANANAS
|
Second Session |
San José, Costa Rica, 4 - 8 December 2001 |
BIOTECHNOLOGY AND BANANA PRODUCTION |
II. TISSUE CULTURE AND IN VITRO PROPAGATION
III. POTENTIAL BENEFITS OF BIOTECHNOLOGY
A. RAPID PROPAGATION WITH TISSUE CULTURE TECHNOLOGY
B. PATHOGEN-FREE BANANA PLANTLETS
1. In its First Session the Sub-Group concluded that the Banana Improvement Project (BIP) financed by the Common Fund for Commodities (CFC) had made a major contribution to banana improvement. The Sub-Group reaffirmed its interest in banana improvement through dissemination of information on this subject. This paper summarizes developments in biotechnology as they relate to bananas.
2. Advances in the techniques of micro-propagation by tissue culture have revolutionized the propagation of bananas in the last 30 years. Traditionally, bananas are propagated from lateral shoots: this is relatively simple time-honoured technique but has had the major disadvantage in that many of the banana pests and diseases have been distributed worldwide on plant material. The use of tissue culture enables farmers to plant with material certified as disease and pest free. In many situations this strategy can delay the requirement to use chemical control measures. Unfortunately, tissue culture will not eliminate all of the banana viruses.
3. Most of the commercially grown banana cultivars are selections collected and distributed over the last two millennia. Breeding new varieties is tedious and only in recent years have breeders' selections been distributed and evaluated for farmer and consumer acceptability. Banana exporters have well-defined opinions on what is required in an ideal commercial banana variety and breeders have had difficulty in incorporating other important characteristics into varieties that are acceptable.
4. For the exporter, a replacement for the pest and disease susceptible Cavendish clones must have all the positive post-harvest attributes concerning "green-life" (how long the fruit can be held in the un-ripe state), shelf-life after ripening and consumer acceptability which really means flavour but also cosmetic attractiveness. Some of the disease resistant varieties bred at the Jamaican programme in the 1960s and the dessert varieties of the FHIA (Fundación Hondureña de Investigación Agrícola) programme do not have the shelf-life and flavours comparable with Cavendish and have not been adopted as export bananas. If consumers in tasting panels have only one impression of a banana flavour, that of Cavendish, which has been the only ripe banana on sale for most peoples' life time, it is not surprising that bananas with slightly different flavours may be less favoured simply because they do not taste like a "typical" banana!
5. All of the varieties of dessert bananas grown for export are similar, forming a group known as Cavendish (Musa AAA). The different varieties represent relatively minor mutations that have affected plant stature and performance. It is not possible to separate these varieties on the taste of the fruit. What is worrying is the fact that because they are of almost identical genotype they are susceptible to the same pests and diseases. New advances in genetic engineering could enable these favoured varieties to be improved through introduction of specific characters such as disease resistance without changing other attributes.
6. The technique of tissue culture began through research on two different needs. Banana breeders, faced with poor seed germination from modest seed yields developed techniques to grow embryos on defined media; and in China, Province of Taiwan, techniques of in vitro culture were developed to produce large numbers of plants free of the fungus Fusarium oxysporum fsp cubense race 4 which threatens commercial producers of Cavendish bananas in some environments. The development of rapid in vitro culture soon spread and the commercial opportunities for supplying the producers of export (Cavendish) bananas with uniform planting material free of pests and diseases were grasped by emergent tissue culture laboratories throughout the world.
7. Modern techniques have and will continue to widen the understanding of the taxonomy of bananas. Hitherto, considerable advances in differentiating the varieties on morphological characters has enabled the unravelling of the origins of the wider groups but it continues to be difficult to use morphology for differentiating clones of similar ancestry.
8. The difficulties associated with conventional breeding led to the exploration of other techniques for introducing useful characteristics into otherwise reliable clones. Mutations can be induced with chemicals, irradiation and also in tissue culture. The strategy is not without difficulties of a practical nature as it involves the production and subsequent growth and observation of large numbers of individual plants from which selections are made. Despite some considerable effort and some limited success for the rather special situation existing in China, Province of Taiwan, there have been no major breakthroughs, and no clones derived by mutation techniques are currently in widespread commercial use.
9. Genetic engineering allows the delivery of a genetic construct conferring some pest or disease resistance or chemical, physiologic or agronomic feature into an otherwise ideal clone. There is much contemporary research directed at perfecting a number of methods of achieving this.
10. Tissue culture has revolutionized banana cultivation and has replaced the use of conventional vegetative suckers in many of the intensive banana-growing regions. It is estimated that up to 50 million tissue cultured plants are produced annually. The technique enables the mass production of clones at a far greater rate than by the collection of suckers from growing plants. Newly weaned plantlets are tender and require good management in the weeks following removal from the growing medium, but once planted in the field and established, their growth and ultimate yield are superior to plants produced by the traditional means. It is thought that the vigour and yield potential is due to the juvenile nature of the material and the increased photosynthetic efficiency, increased functional leaf areas, increased root vigour and total dry mass accumulation compared to the conventionally produced plants. The improvement in fruit yields from tissue cultured plants can persist for three harvests.
11. The use of tissue culture planting material can prolong the pest-free period for months or possibly years. The ubiquitous pests Radopholus similis, the burrowing nematode and Cosmopolites sordidus, the banana weevil are examples of problems that have arrived with the crop. Both pests originate in the Pacific region and have become established wherever bananas are grown and the climate is favourable. Because these pests are not native to most banana growing countries, land hitherto not planted with bananas will not be infested. The nematode has few other host plants and the weevil has none. Once the weevil is introduced it is difficult to eliminate. Wherever bananas are to be grown for the first time, use of tissue cultured plants would avoid the introduction of the pests into the newly cultivated areas.
12. The problem of viruses has not been solved by tissue culture and the international movement of some germplasm is and will continue to be restricted until satisfactory methods of virus elimination have been developed. Banana streak virus (BSV) is a particular problem as it cannot be eliminated by the conventional techniques of heat treatment or apical tip culture.
13. All of the early commercial development with tissue culture was on the Cavendish clones upon which the international export trade depends. The developments with in vitro production of other dessert, cooking and plantain varieties have been less. In fact other varieties may require subtle differences in the growing conditions in tissue culture. Banana genotypes respond differently in the rates of proliferation in vitro, and inevitably, the costs for producing specialist varieties will be greater. This suggests that non-export producers may have to depend upon government or NGO-funded tissue culture laboratories and possibly subsidies or promotional inducements.
14. Tissue culture laboratories are relatively cheap to establish, a modest facility could cost US$50 000 to equip. A laboratory in South Africa is now mass-producing the Cavendish varieties, plantains and some of the new FHIA "hybrids" at individual plant costs of about US$0.70, significantly cheaper than production costs in Europe.
15. Projects to support and promote the replanting and rehabilitation of bananas through the introduction of "clean" planting material and "improved" genotypes have begun in East Africa through national and international programmes. Similar work has been carried out in FHIA in Honduras. This may help to solve the problems of weevils, nematodes and Black Sigatoka leaf-spot disease (Mycosphaerella fijiensis) which cannot otherwise be effectively controlled in the African banana-based farming systems.
16. The complex nature of the commercial banana clones has bedevilled breeders for many years. The difficulty in making hybridizations (because some clones are tripolid and sterile) has prevented the predictions of gene transfer, particularly those conferring disease resistance. The gene(s) for resistance to Fusarium oxysporum fsp cubense, Mycosphaerella spp and nematodes have not been identified. This has promoted interest in introducing "resistance" genes from other (non-banana) sources. Sequencing the genome of bananas should lead eventually to the recognition of the vital genes which may then be utilized. One can assume that no new banana variety can be released if it does not have resistance to Fusarium and at least some good tolerance to leaf-spot diseases and perhaps nematodes. FHIA might, with justification, argue that these goals had been achieved with conventional breeding. It is a testimony to the late Dr Phil Rowe that several hybrids produced by the FHIA breeding programme in Honduras are being cultivated and accepted by farmers and consumers in Cuba and some African countries.
17. Understanding of the functions of the genetic components of the banana genome would provide the basis for developing and selecting clones with qualities enabling the crop to be grown in more demanding environments. Additionally, clones with improved post-harvest qualities and desirable fruit characteristics would be sought.
18. Commercial export producers of the dessert Cavendish varieties grown as a monocrop in West Africa, the Caribbean and Latin America depend heavily on fungicides to manage the leaf-spot diseases (M. fijiensis M. musicola) and nematicides to control nematodes. This strategy is neither feasible nor desirable for farmers supplying local markets. Faced with the need to make these regular pesticide applications, commercial producers can reduce the nematicide schedule if new plantings are made with clean material in land that has been left fallow or cropped with appropriate non-host crops for a 12-18 month period. The risk of re-infection from adjacent plots will remain, so eventually, nematicides will need to be introduced. Clean planting material will not diminish the presence of leaf-spot diseases. The frequency of fungicide use might be reduced by more stringent disease monitoring and perhaps mixed cropping but in environments where the diseases thrive the only real alternative to fungicides is improved (disease resistant ) varieties which the export fruit producers desperately need. There has been some suggestion that it might be feasible to envisage a system where Cavendish for export is grown alongside multi-purpose disease resistant (FHIA1) bananas for local markets as a means to reduce the spore inoculum potential in the plantation.
19. The time scale of research is undoubtedly long: it will be surprising if these "ideal" clones can be developed in less than 15 years. The driving force will have to be the economic and commercial requirements of the banana export industry. However, several social and environmental issues still need to be resolved. The human risks of transformed bananas with anti-fungal or nematode toxins expressed in leaves or roots are probably small. Risks to the environment are even less likely because many of the banana varieties (like Cavendish) are sterile. Transgene escapes are thus considered a minor risk particularly in relation to the large dependence on pesticides.
20. On 19 July 2001 scientists of eleven countries announced the founding of an international consortium to sequence the banana genome within five years. This effort is to be coordinated by INIBAP (International Network for the Improvement of Banana and Plantain). The fact that research continues in universities, within the INIBAP framework of research institutions and national research services implies that advances will be disseminated in a manner which makes new varieties or other advances available to small producers as well as export-oriented plantations.
21. Whilst the technology of tissue culture has now permeated to most countries and is established, the technological developments of improving varieties by genetic engineering are relatively novel and research activities are still largely restricted to specialist laboratories. In the last ten years considerable research effort has been devoted to the possibility of producing a genetically modified banana. Protocols have been developed and such plants have been produced under contained conditions confirming that in principle, bananas can be modified. Research continues to discover the best methods of preparing the basic (parent) plant material for transformation and for the transfer of the required genetic characteristics. This work is being done by commercial companies, universities in the United States and Europe and at research institutes specializing in plant sciences. The cost of this research is high, requiring sophisticated laboratories (with adequate containment facilities) and highly qualified staff. These laboratories and research institutions can be expected to publish the results of their work, making it available to developing countries.
22. Genetic modification is a high profile and contentious subject. The release of a transformed banana variety for commercial production is unlikely to take place for ten years or longer. (One must assume that any "new" variety will go through extensive field evaluation on experimental stations and then farmers' fields. For example, in East Africa it will take at least four years for one plant to complete three flowering generations, a minimum agronomic requirement). Moreover, research results need to be disseminated by international organizations and research institutions at no cost to the developing countries where bananas are produced. In those instances where private research results in patented products or processes royalties may have to be paid for that intellectual property. In many cases it is these potential royalties which stimulate needed research.
23. Commercial farmers desperately need varieties with resistance to fungus leaf-spots, nematodes and in some locations weevils. These farmers are likely to be able to pay for the transformation technology as they will expect to be spared the costs of multiple fungicidal applications and at least two nematicide applications per annum which could be in the region of US$1 000 or more per hectare.
24. For small producers meeting internal food needs losses to pests and diseases can be reduced as well, nutrient efficiency can be improved along with productivity. Value-added products can follow on with prolonged shelf-life. Extended crop seasons and areas can stimulate production to meet growing food demand. In the long run sustainability may be enhanced.
25. There is an opinion within the international banana trade that only Cavendish varieties have the quality that the consumer in Northern Hemisphere importing countries wants. Thus far consumers have not accepted bananas which taste different from Cavendish. Therefore one can expect research and development to continue its concentration on Cavendish varieties.
26. Farmers supplying local markets with a diversity of banana types (dessert, cooking, brewing and plantains) who do not usually make use of chemical treatments also need access to resistant clones but would not have the financial resources to pay for the technology. Here again, dissemination of research results to farmers producing for local markets becomes a key element in successful transformation of research into practical food security. There is a direct and clear linkage between disease resistant varieties and increased yields for farmers producing for local consumption, both in bananas and plantains.
27. The transformation of all the varieties currently grown in countries such as Uganda or India where there is a great diversity that meets specific preferences is unlikely. However, if such technological developments are successful, this could lead to the eventual loss of genetic diversity, a worry that is already being addressed by INIBAP as old inherently less productive clones are forgotten or discarded as peoples' preferences change. Producer interests are to retain varietal diversity while incorporating new developments which enhance productivity.
28. Perhaps biotechnology can offer a new opportunity for food security where bananas are important sources of food, particularly among smallholders in developing countries. If many different genes for disease resistance, controlled ripening and so forth were developed, and many different clones of banana with different genes were available to smallholders, the risk of unpredicted, widespread damage by any one new disease would be small. In this sense, biotechnology could actually improve the situation of small farmers, by controlled ripening for example, permitting the extension of the season and making more fruit available for local consumption over longer periods.
29. In some major markets, the public perception of genetic modification is of disfavour. Perhaps, if put in terms of environmental protection and worker safety, consumers would better appreciate that there are benefits beyond improved productivity in applying these techniques to bananas. In bananas, the most compelling reason for adopting genetic transformation is to reduce the use of fungicides and insecticides. It is for these constraints that genetic constructs are already recognized and attempts at their incorporation in Cavendish (and other bananas) may have been advanced but is protected under commercial secrecy agreements. The resistance traits based on protease inhibition will be expressed in roots (for nematodes) and anti-fungal compounds in the leaves for the leaf-spot diseases.
30. The application of fungicides through spraying by aeroplanes has long been identified as detrimental to worker and local population health by environmental groups. Chemical run-off into local streams has also been considered a problem for some time. From the environmental point of view, developments which reduce the side effects of intensive banana cultivation can be considered positive. One concern regarding the environment is that genes from such traits as resistance to herbicides or to insects will escape into the local flora, so damaging the natural environment. These are issues when one discusses most crops; however, since banana plants do not produce pollen, being sterile, the question of dispersal into the environment of genes in transformed bananas does not arise.
31. However, consumer wariness, particularly in Europe, may continue to play a significant role in the introduction of transgenic crops and/or varieties, in spite of the benefits to producers and workers, unless consumers are clearly aware of any risks. Consumers are demanding choice with regard to transgenic crops and/or varieties. Risk assessment decisions need to be based on good science.
32. Traditional labels are based on content, but some consumers are interested in the method of manufacture, or in the case of crops, whether they were grown with gene technology. Any traceability requirements would have to be factored into the costs of genetically modified bananas if and when they come onto the market. The complex issue of labelling opens many areas for debate over which altered characteristics have to be communicated to the consumer.
33. The next five to ten years could be an exciting time for the banana industry as biotechnology is applied to this crop which is so important to the food security of so many people in developing countries (also see documents CCP: BA/TF 01/4, CCP: BA/TF 01/CRS.5 and CCP: BA/TF 01/CRS.6 ) and which creates income for a long chain of people engaged in the production and trade in the product. Breakthroughs can be anticipated, and hopefully these will lead to: reduced environmental impacts by chemicals now necessarily applied in production areas; lower costs of production; improved worker safety; and higher productivity. However, the realization of these benefits will depend on the verification of limited risks to the environment and to consumers (a prerequisite for consumer and trade acceptance). Over time the Sub-Group may wish to play a role in this effort, as there are potential benefits to growers, traders and consumers. Transparency and information are fundamental goals of the Sub-Group, and this is clearly an area where a role can be played.
34. On 14 May 2001 FAO Director-General Mr Jacques Diouf said "Whereas GM technologies offer great opportunity to develop a world that is truly food secure, we must not forget that we all - the scientific community, the international community, the multinational life science companies and the donor community together with national governments - bear a fundamental responsibility to ensure that the developing countries can equitably share in these exciting advances that science offers in a way that is safe for their population and environment. This calls for a more open, integrated and collaborative involvement of all the stakeholders engaged in developing country agriculture and food production." Bananas are very much a part of this opportunity.
