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Philippe Boxus
Agricultural Research Centre,Biotechnology Department,Gembloux
- Belgium
partment,Gembloux
- Belgium
Introduction
All artificial manipulation made on a plant, or only on a part of a plant, could refer to "plant biotechnology". In our review, we shall separate the numerous plant biotechnology applications into two groups.
The first group is related to tissue culture and go from a single cell, or a specific tissue, to the whole plant. These technologies are founded on a very old concept "the cellular totipotency", stated by Haberlandt (1902), but only demonstrated by Steward in 1958. His research team was the first to be able to transform a carrot cell line in some "artificial embryos, later called "somatic embryos".
The applications of the second group are more recent and derive
from on excellent knowledge of the double helicoidal DNA structure
proposed in 1953, by James Watson and Francis Crick. They base
their strategy on the molecular biology science.
Chapter 1. : Horticultural biotechnologies related to tissue culture.
The development of plant biotechnology has been related to the discovery of the growth regulators and their progressive introduction in tissue culture. In 1934, in the States, white was producing continuous growth of in vitro tomato roots. After that, went and Thiman's work on auxin, Gautheret in France (1935) and white in US (1938) were auxin, Gautheret in France (1935) and white in US (1938) were able to obtain division of isolated cells from Salix and tobacco, and finally to maintain undefined cell lines.
In 1957, Skoog and Miller demonstrated that 6-furfurylaminopurine, a cytokinin isolated from a DNA hydrolysate, could induce some caulogenesis, but also that the cytokinin/auxin balance could start different morphological programmes. A ratio higher than one unit induced caulogenesis, a ratio inferior at this unit induced roots.
On this basis, a multibillion dollar industry was created. Hundreds of small and large nurseries and biotech labs throughout the world are propagating in vitro more than 1000 different plant species (Bajaj, 1991).
This micropropagation technique offers not only means for mass propagation, but also plays an important role to conserve elite or rare plants that are threatened with extinction. Moreover, meristem tip culture offers the possibility of virus eradication. These technologies started about 20 to 25 years ago, especially for ornamental plants, and for a few other crops : potato, strawberry, bananas, ... Propagated clonally, it was very important to have a true to type propagation technique.
On the other hand, it's also possible to use tissue or cell culture
to increase genetic variability. Undifferentiated cells obtained
from callus, cells or protoplasts culture are produced and submitted
to an selective pressure to improve a and submitted
to an selective pressure to improve and fix the somaclonal variants.
1. Production of true to type plant.
1.1. Meristem tip culture.
1.1.1. Production of virus-free plants.
In 1952 Morel and Martin were successfun in regenerating a virus-free dahlia plant by the excision of some meristematic domes from virus infected shoots. Three years later, the same authors were able to eliminate virus A and Y from virus infected potato. Semal and Lepoivre (1992) reported that a virus-free sweet potato was producing 40T/ha in China by comparison of the 20 T/ha produced before meristem culture.
Virus eradication is dependent on several parameters. But to take advantage of the non uniform and imperfect virus distribution in the host plant body, the size of the excised meristem should be as small as possible. For Stone (1963), only tips between 0.2 and 0.5 mm most frequently produce virus free carnation plants. The explants smaller than 0.2 mm can't survive, and those larger than 0.7 produce plants that still contain mottle virus.
Today, no definitive explanation can be given to understand this
virus eradication (Wang & Charles, 1991). various explanations
have been given : absence of plasmodesm in the meristematic domes,
competition between synthesis of nucleoproteins for cellular division
and viral replication, inhibitor substances, absence of enzymes
preiral replication, inhibitor substances, absence of enzymes
present only in the cells of the meristematic zones, and suppression
by excision of small meristematic domes. This last proposal could
explain why some potato plant showing virus particles in the meristematic
domes, could regenerate a virus free plant (Mellor & Stace
Smith, 1977).
1.1.2. Shoot tip micrografting
When meristem tip culture fails, it is possible to graft small meristematic domes on young seedlings growing in vitro. In this way, Navarro et al. (1975) eradicated all the virus diseases from Spanish Citrus orchards.
This technique was also very successful in eliminating virus diseases
from peach trees (Mosella et al 1980).
1.1.3. Factors influencing virus elimination
The success in virus elimination depends on the choice of the explants, the virus, temperature,....In general a high temperature (37C) is effective for virus diseases, but is depressive for viroids.
The introduction of virus inhibitors (ribavirin) into the culture
medium can't inactivate the viruses, but it prevents their replication.
A combination of cytokinin and ribavirin, or a heat treatment
in vitro, are sometimes used with success to inactivate some viruses
difficult to eliminate by meristem culture (NRSV, PDV,..).
1.2. Micropropagation techniques
During the micropropagation process, the genetic stabilit
During the micropropagation process, the genetic stability of the new shoots is dependent upon their origin. Axillary shoots issue from pre-existing buds and are normally true to type, indeed the meristematic cells are genetically very stable.
Adventitious shoots, such as somatic embryos, are neoformed buds
developed directly on some organs, or indirectly through a callus
phase formed on this organ. So, if the mother plant presents a
cell mosaic or chimaeric tissues, risks of genetic variation exists.
It is similar in the case of an indirect regeneration, when the
callus phase is too long.
1.2.1. Propagation by axillary shooting
This technique has proved to be the most applicable and reliable method of in vitro propagation. Axillary shoot growth is stimulated by overcoming apical meristem dominance.
Commercial tissue culture laboratories are now able to propagate
a large number of herbaceous ornamental species and several woody
plants in this way. However, the propagation of Pelargonium, Howea,
and a few other horticultural plants are always difficult to propagate
by axillary branching.
1.2.2. Propagation by direct or indirect organogenesis.
Adventitious shoots could arise directly from the tissue of explants without callus formation. Several plants of the family gesneriaceae (Saintpaulia, Streptocarpus,...) regenerate directly buds on leaf explants, likewise Lilium rnerate directly buds on leaf explants, likewise Lilium regenerates on scales.
However more often, like for Ficus lyrata, adventitious buds appear
on callus. While coffee, cocoa trees, and many conifers are produced
by somatic embryogenesis developed on callus or cell suspensions.
1.2.3. Constraints of in vitro micropropagation
The establishment of axenic culture could be difficult when the explants are coming from hot and humid countries. Moreover, in the course of micropropagation several authors observed a sudden appearance of endogeneous bacteria (Cassels, 1997). Nevertheless only Holland and Pollaco (1994) have demonstrated the presence of this kind of bacteria in more than 70 different species.
For Leifert and Woodward (1997), the major source of contamination is the initial explant. They add that microbial contamination in commercial plant tissue culture laboratories is the most important cause of losses. For this reason, they support the introduction of a microbiological production control strategy.
A second important constraint during the initial phase mainly concerns woody plants. A mature tree must be rejuvenated to recover its morphogenetic competence. Franclet (1981) described various treatments, micrografts, cascade grafts, cytokinin treatments to reverse the adult phase to juvenile. The micropropagation of Acacia Senegal was only possible after rejuvenation by micrografting (Palmnly possible after rejuvenation by micrografting (Palma et al. 1997).
A distinction between chronological, ontogenic and physiological
age (Monteuuis 1989) is needed to understand the rejuvenation
concept. This was definitively demonstrated after a complete reversion
of Sequoia sempervivens (Franclet & Franclet Mirvaux, 1992).
1.2.4. Improvement of axillary branching
The cost of micropropagated plantlets is also an important limitation of the techniques. In New Zealand, where they produce 2-3 million micropropagated radiata pine per annum, the relative cost of micropropagated planting stock had dropped from 13,8 times the cost of seedlings in 1988 to 6,9 by 1993 (Smith, 1997).
To reduce manpower costs, several improvements have been proposed. The more simple method was in vitro layering developed by Wang (1977) to clone PVX-free potato plants. The first plantlets placed on the medium in a horizontal position developed axillary shoots. They are harvested by cutting one centimeter above the medium surface, at 3 weeks intervals. A similar technique called 'hedging system ' by Aitken Christie and Jones (1987) was later used to produce Pinus radiata.
Ziv (1990) proposed for corm plants, Gladiolus and Nerine, a very rapid propagation system. She reduces the internodes and leaves by introduction of an anti-gibberellin agent in the medium. Finally, only aggregates of buds are formed, then they inally, only aggregates of buds are formed, then they are divided and introduced in bioreactors for mass production. Similar systems were developed in Gembloux, to propagate carub trees and asparagus.
Since 1988, Duhem was producing very large quantities of Eucalyptus
plantlets in Petri dishes without anti-gibberellin but in complete
darkness. Transfers from one Petri to another is made by a simple
squashing (Boxus et al, 1991).
1.2.5. Somatic embryogenesis propagation
For genetically stable species, somatic embryogenesis offers a very fast scaling-up system, especially when it's possible to produce embryos in bioreactors. Unfortunately this production via fermentors was not as simple as first envisaged. And today, only a few model plants are successfully produced by such technology : carrot, celery. Other applications remain at the experimental stage : coffee, oil, palms, conifers, Euphorbia pulcherrima,... and several other horticultural species.
Several bottlenecks limit the use of this interesting technology. One of the main problems is genetic stability. So, despite the clonal nature of nucellar embryos, different morphological anomalies can occur among mango somatic embryos, as it was also observed in Citrus plants derived from nucellar cultures (Litz et al., 1993).
Another difficulty is the loss of embryogenic capacity over time,
a phenomenon observed with different species. It is als
a phenomenon observed with different species. It is also important
to note that somatic embryogenic lines of conifers are always
originated from immature embryos.
1.2.6. Artificial seeds
Another very interesting possibility of the somatic embryogenesis technology has been developed during the past fifteen years by Redenbaugh and his team (1991, 1993). They were able to encapsulate somatic embryos by hydrogel coatings (sodium alginate), producing single embryo artifical seeds.
To date, some improvements offer the possibility to directly plant
the artificial seeds in the greenhouse on special substrates (vermiculite,
sans,...). This methodology will provide in the future a good
technique to reduce the cost of transplants.
1.2.7. Gene bank
Tissue culture methods offer the opportunity for in vitro collecting, rapid multiplication and distribution of important, elite, or rare plants that are threatened with extinction. The two major in vitro storage strategies are slow growth and cryopreservation.
Since the first results of Seibert (1976), who was able to initiate shoots from carnation shoot apices frozen to -196C, this technique is now successful for many of horticultural species. Dereuddre et al. (1991 ) have provided a very simple technology to freeze encapsulated meristems in dried alginate beads. It works for pear, strawberry, eucalyptus, potato,....
Some ior pear, strawberry, eucalyptus, potato,....
Some international institutions have very large collections of old and current varieties, available for exchange and introduction in crop improvement programmes. The International Potato Center (CIP) in Lima, Peru, has a large world potato collection. Germplasm of sweet potato and cassava is at the International Institute of Tropical Agriculture (I I T A), Ibadan, Nigeria.
The movement of germplasm involves the risks of accidentally introducing
plant quarantine pests along with the host plant material. To
limit these risks, the plant material should be transferred from
one country to another as in vitro cultures through a transit
Centre, where it should be indexed. For bananas, in the framework
of INIBAP, the transit Centre is the Catholic University of Leuven
in Belgium where a very large in vitro germplasm exists.
2. Tissue Culture Techniques to increase genetic variability
2.1. Somaclonal variations
The production of plantlets by callus regeneration, cell suspensions,
protoplast cultures, could present some deviations with regard
to the mother plant. This is a way to increase the genetic variability.
Associated with a selective pressure (stress to toxins, pH, salinity,
cold,...) it's used to obtain resistant lines. Indeed, after regeneration,
plants can express new potentialities rarely obtained another
way. Stable and profitable variants are seleanother
way. Stable and profitable variants are selected and introduced
in breeding programmes. In 1976, a Pelargonium cv Velvet Rose
was created by this technique (Reisch, 1983). Later, other applications
were described, as in sugarcane, tomato, red pepper,... Following
Sibi (1994), extrachromosomic systems must be involved to explain
the genetic behaviour of some new expressed tissue culture characteristics.
She uses the term "epigenic" to evoke a whole of hereditary
elements which belongs to the cytoplasmic or nuclear compartments,
but are not transmitted by mendelian rules.
2.2. Haplodiploïdisation
Many species are able to produce haploïds through different in vitro techniques. The oldest was anther culture of androgenesis. To date, the results vary considerably from one species to another. Solanae (datura, tobacco, red pepper, eggplant, petunia), cereals (wheat, barley, rice, triticale, maize) or crucifers (soybean, cabbage) are species easy to regenerate by anther culture. To the contrary, tomatoes, leguminous, or Compositae are recalcitrant.
Ovule culture, or gynogenesis, was a successful technique for Gerbera, beet, courgette,...However, the most common technique is pollination with irradiated pollen, in order to induce in vivo parthenogenesis. The oospheres developed in embryos without fertilisation are saved by embryo rescue.
The haploid plantlets (n chromosomes) are tre.
The haploid plantlets (n chromosomes) are treated with colchicine to produce fertile homozygous lines, called "double haploid lines". This haplodiploïdisation technique could give immediately new elite genotypes, hybrid parents after in vitro propagation, as asparagus supermales (MM), or useful genetic material to establish gene mapping.
A good synthesis book concerning all these possibilites was published
by Bajaj (1990).
2.3. Protoplast culture
Protoplasts are the smallest units able to regenerate a whole plant. Therefore protoplasts cultures can serve to enlarge genetic variability by introducing somaclonal variation. However, the main interest of protoplasts, is their capacity to fuse and to produce hybrids or cybrids, new organisms most often unknown in nature. Indeed, protoplasts allow to transgress the barrier of the botanical species or genus. Naked protoplasts can accept without rejection external elements : nuclei, cytoplasmic corganelles, liposomes,.... containing genetic information. The first protoplast fusion application was a cytoplasmic transfer from one genotype to another to induce male sterility (CMS) from mitochondrial origin. These male sterile hybrids are interesting to produce F1 hybrids (Brassica, Cichorium,...).
Another cytoplasmic transfer concerns the introduction of chloroplastic DNA to induce herbicide (atrazine) resistance, from Solanum nigrun duce herbicide (atrazine) resistance, from Solanum nigrun to tomato for instance (Jain et al. 1988).
Many intergeneric and interspecific hybridations are possible
but not always profitable because these hybrids are too often
infertile. This problem does not exist if we can vegetatively
propagate the hybrids, as in the case of Citrus rootstocks. In
Florida, Grosser (1990) was able to analyse several thousand Citrus
hybrids.
Chapter 2 : Contributions of molecular biology in horticulture.
More and more pathologists are using molecular probes for early
detection of diseases. However, the main contributions of modern
biotechnology remain probably in the hands of the plant breeders.
Indeed, molecular markers are of great use in detecting desirable
new genes, or to identify important QTL. This marker-assisted
selection is very useful for many vegetable plants. Other applications
are DNA - fingerprinting and genetic engineering. This recent
technology aims to insert and to express new specific genes into
a selected plants.
1. Marker-assisted selection
Molecular markers and genome mapping will reach a large extension in the next breeding programmes of tomatoes, peas, cabbages, melons, potatoes,...
It will be possible to improve the speed and the incorporation efficiency of desirable new genes by utilizing of closely linked selectable molecular markers genes by utilizing of closely linked selectable molecular markers. The number of backcross will be reduced. Tanksley et al. (1981) show that only with 12 markers, one on each tomato chromosome, the composition of the recurrent parent genome is similar to that observed in the absence of selection after the third backcross two years later. Therefore, it's easy to understand the high improvement that we can get with the 700 tomato markers already known in 1990 for this crop (De Verna and Paterson, 1990).
The utilization of molecular markers could also identify important
quantitative trait loci (QTL). Recently Foolad and Chen (1998)
have identified 13 RAPD markers at eight genomic regions, that
were associated with QTLs affecting salt tolerance during germination
in tomato.
2. DNA fingerprinting
The DNA polymorphism observed by RFLP, AFLP, or RAPD, allows cultivar
identification of fruit trees, apple, citrus,... or other vegetatively
propagated plants. Although some mutants, as coloured fruits,
escape these identification techniques, some people would evaluate
the genetic uniformity of regenerated plants in this way.
3. Genetic engineering
Genetic engineering consists of introducing a foreign gene into
a plant genome to create a new function. Or at the contrary, it
could be to reduce or suppress an existing gene function, as in
the antisense strategy.
3.1.ene function, as in
the antisense strategy.
3.1. Historic
In this field, progress were very rapid. In 1974 the pathogenicity
of Agrobacterium tumefaciens, due to a large plasmid called Ti,
was demonstrated. In 1977, Chilton et al. demonstrate a stable
incorporation of plasmid Ti-DNA into higher plant cells. In 1983,
the team of Van Montagu and Schell in Gent succeeded in producing
a transgenic plant, and eleven years later the first transgenic
cultivars were available in the market.
3.2. Transgenic plants with new agronomic traits
Two different techniques are commonly used to introduce genetic information (DNA) inside cells, protected by pectocellulosic walls. A particle bombardment process, called biolistic, is used with success for monocots gynmosperm, squash, peas,...Today, this technique allows the bombardment of meristems and avoids the difficulties of regeneration. But the mediation of Agrobacterium remains till now the most routinely system to transform dicotyledonous plants.
The main agronomic traits introduced in horticultural plants and
already commercialised are Bt toxin and herbicide resistance.
Other studies concern virus resistance, male sterility, ....
3.3. Antisense strategy
Calgene created in 1994 the first commercial transgenic plant, a long shelf life tomato, by the suppression of polygalacturonase activity due to an antisense gene (Smith, 1988). However, t activity due to an antisense gene (Smith, 1988). However, this Flavr Savr tomato variety was removed from the trade 3 years later, because of its disease susceptibility and its lack of productivity !
Later, other tomato varieties with long storage qualities were obtained by the utilization of an antisense RNA inhibition of ACC synthase or ACC oxydase, two ethylene precursors.
The antisense technique was also used to reduce the lignification
of woody plants, by blocking the enzymes involved in the precursor
of lignin biosynthesis. Another interesting application wsa the
induction of white flowers in petunia and in different other ornamental
plants by the suppression of chalcone synthase activity.
3.4. Transmission of the new traits
These traits induced by the transferred DNA are transmitted to
the progeny as a dominant Mendelian character. Nevertheless in
some cases, transgenic plants with a strong gene expression can
generate progenies with only a faint no gene expression. This
problem is not clearly elucidate.
3.5. Marker, reporter, promotor and expression genes
To select the transformed cells, some marker genes, very often resistant to antibiotics or to herbicides, are attached to the coding sequence, as a promoter or an expression gene. Those allow the new gene to express in the whole plant or in a specific plant tissue.
Some reporter genes are used to follow the evolution oe.
Some reporter genes are used to follow the evolution of the transformed cells. The most frequent reporter genes are the gene "gus" (( - glucoronidase) or the gene lux (luciferase).
3.6. Horticultural transgenic crops already released in USA.
The Flavr Savr tomato was the first genetically engineered whole food approved for commercial sale in 1994. Four other transgenic tomatoes with a delayed ripening were approved later (1995 and 1996).
In 1995, potatoes with Bt genes and a squash cultivar resistant to two viruses were released. Two years later, another squash cultivar resistant to 3 viruses and a papaya line also resistant to viruses were approved.
Two other horticultural crops are waiting the authorities approval : red hearted cichory (Radicchio) with male sterility and resistance to herbicide, and a tomato with Bt toxin.
It there are so few commercial transgenic plants in horticulture, it's probably due to the relatively low acreage of these horticultural crops in comparison with other agricultural crops. In 1997, in the world 5 million ha were planted with glyphosate resistant soybeans released by Monsanto alone.
Nowadays, it's true also that many transgenic plants exist in
research laboratories, awaiting authorization for field testing,
as they are very interesting model plants for learning physiology
: lettuce with less nitrate by increasing nitrate reductase gene
activi with less nitrate by increasing nitrate reductase gene
activity, a yeast ribonuclease gene to reduce viroid infection
on potato, modification of lignin synthesis in plant to produce
trees adapted to paper industry, or timber, or biomases production,
regulation genes to control tree architecture,....
Chapter 3 : Situation of biotechnologies in the world : development and risks
1. Situation in the young countries or in developing countries.
A general use of in vitro micropropagation in the developing countries is now a reality, as it was predicted by Albert Sasson (1993). African countries for instance are producing potatoe, banana, cassava,...
Even the production of transgenic plants is no longer a prerogative of the Northern countries. Different experiments are now starting in the South, specially in the international laboratories from CGIAR. Although CGIAR's expenditures on biotechnology for 1997 raise only 24.2 million US$ on an annual budget of 345 million US$ (Biotechnology and Development Monitor, December 1997, 33, pp12-17) this Consultative Group on International Agricultural Research plays a very important role as contributor to agricultural research for developing countries.
The large international research centres IITA (Ibadan, Nigeria), CIP (Lima, Peru), CIAT (Cali, Columbia),... belong to the CGIAR. Their roles and NGO's are primordial. The genetic transformatheir roles and NGO's are primordial. The genetic transformation of cassava is an excellent example. Its tuberous roots provide food for over 500 million people, mostly small-scale farmers. Unfortunately, till recently this integral plant for food security in developing countries has been recalcitrant to transformation approaches. However, thanks to the participation of international institutes located in cassava growing countries, CIAT and IITA with the help of four development associations from Swiss, UK, The Netherlands and USA, were able to initiate procotols for cassava transformation and regeneration, (Biotechnology and Developement Monitor, March 1997, 30, pp. 16-18).
Other networks, like the Cassava Biotechnology Network (CBN) previously described, exist. REDBIO, a technical cooperation network on plant biotechnology, is supported by FAO to promote a best use of scarce manpower, equipment and other resources in Latin America.
On the other hand, more and more private laboratories exist in the developing countries which have a high scientific and technical level (China, Singapore, Taiwan, India, Brasil, Mexico, Chile,...). In these countries, European, American or Japanese agrochemical companies are investing. Also these countries will have their chance to develop their own technologies, and to export to the Northern markets.
Meanwhile, genetic engineering techniques are being applied mainly to crops which are important for g applied mainly to crops which are important for the industrialized world, not crops on which the world's hungry depend. Therefore, it is unrealistic when Monsanto writes "the experts said that biotechnological innovation will increase the crop productivity without occupation of new lands, saving tropical forest of best quality and animal habitat". However, the World Bank was promising in a 1997 publication Bioengineering of crops that" transgenic crops could improve food yield by up to 25 per cent in the developing countries and could help to feed an estimated additional three billion people over the next 30 years".
But, not all people are confident in this prospective. To the contrary, some are afraid that the poorest countries, where more than 700 million people are chronically undernourished will miss the biotechnological revolution (see " a second green revolution draws closer" by JJ. Perrier, Biofutur, 169, 14-26, 1977).
Nevertheless, there is some hope to transfer to the developing
countries high technology, which don't undermine the environmental
and social network. So, the Agricultural Biotechnology for Sustainable
Productivity Project (ABSP project) is managed by Michigan University.
Four American universities, two research centres from France and
USA, and two American private companies are also involved in this
project. The ABSP's objectives are the reduction of losses due
to pathogens anre the reduction of losses due
to pathogens and pests by using transgenic plants (sweet potatoes,
potatoes, cucurbits, tomatoes) and by cloning commercial value-plants
(bananas, pineapple, coffee).
2. Situation in the Northern countries.
2.1. Mass propagation
In 1988, Pierik (1991) predicted a European in vitro propagation of 212 million plantlets/year. He was also predicting an important development of this activity for the future. Following Pierik this quantity accounted for only 5 % of the plants able to be propagated by vegetative means. However a few years later Pierik's prediction was not confirmed . The world production was estimated at 600 million. In USA, Zimmerman (1997) was recording a production of 121 million plantlets for a total of 110 laboratories, half produced in 11 laboratories, and 6 labs were propagating each more than 6 million plants per year.
In Europe, only the Dutch production of micropropagated plants
is precisely known. In 1990 the total production was 95.5 million.
In 1995, the Dutch in country production reached only 53,7 million,
whereas importations increased 77,3 million. (37 million from
Poland and 17,1 million from India) (Pierik, data unpublished).
These laboratory relocations to low-cost manpower countries are
commonly observed, and put the question of the quality management.
2.2. Transgenics
The GMOs invade progre
2.2. Transgenics
The GMOs invade progressively all the US lands : 1.6 % in 1996, 15 % in 1997, 50 % in 2000..... It will represent an estimated market of 3,9 million US$ in 2003 ! The largestt agrochemical companies are merging to become giants of agrobusiness such as Novartis, Monsanto, Zeneca,...
Following Monsanto in 1996, about 950 T insecticides were saved
by introduction of resistant cotton, id est a net savings of 81
US$/ha for the grower. Glyphosate-resistant soybeans (4 milion
ha in 1997) allow a savomgs of 44 to 49 US$/ha. (Information from
cultivar, suppl. n 436, Feb. 16, pp. 24-37, 1998).
3. Perspectives, limitations and environmental risks
Ecological impact related with the introduction of GMOs is always an open debate.
The application to agriculture of these new technologies certainly opens interesting perspectives, but also raises potential problems. The risk of crop transgene spreading has been demonstrated. A researcher of Clemson University in South Carolina reported "that in a population of wild strawberries growing within 50 meters of a strawberry field, more than 50 % of the wild plants contained marker genes from the cultivated strawberries" (Kling J. 1996).
A Danish team (Mikkelsen et al, 1996) have shown a possible rapid spread of genes from oilseed rape to the weedy relative Brassica campestris.
There are other risks. Brassica campestris.
There are other risks. The introduction of Bt gene allows a drastic reduction in the use of toxic chemicals for crop protection. But a poorly controlled use of Bt-technology can destroy more effectively the predators than the pests. Or when" many crop plants are transformed with similar effective traits, in such situation, many polyphagous pest species, which by nature are more flexible evolutionarily than those that have a narrower diet, are likely to overcome Bt resistance very quickly". (Hokkanen, 1998).
Therefore, before releasing a transgenic plant, any risk has to
be weighed against the benefit of the transgenic crops. We must
not forget that annually in the world 500.000 acute pesticide
poisonings, with 5000 deaths, are observed. Some of these estimated
environmental and human health benefits potentially provided by
Bt crops are presented in table 1.
Table 1 : Estimated Global Economic, Environmental, and Human Health Benefits of Bt Transgenic Plants. (following Hokkanen, 1998)
|
|
|
| ||
| 1 | 90 | 45 | 45 | 91 | 16 |
| 10 | 900 | 47 | 853 | 917 | 157 |
| 25 | 2250 | 49 | 2201 | 2293 | 394 |
| 50 | 4500 | 51 | 4449 | 4585 | 787 |
Bibliography
AITKEN-CHRISTIE J. & JONES C., 1987. Traphy
AITKEN-CHRISTIE J. & JONES C., 1987. Towards automation : Radiata pine shoot in vitro. Plant Cell Tissue Org. Cult., 8, 185-196.
Bajaj Y.P.S., 1991. Automated micropropagation for en masse production of plants. In : Biotechnology in agriculture and forestry. Vol. 17. High-tech and micropropagation I. Edit. Y.P.S. Bajaj, Springer-Verlag Berlin, Heidelberg, pp 4-16.
BOXUS Ph., TERZI J.M., LIEVENS Ch., PYLYSER M., NGABOYAMAHINA P. & DUHEM K., 1991. Improvement and perspectives of micropropagation techniques applied to some hot climate plants. Acta Hortic. 289, 55-64.
CasselLs A.C., 1997. Pathogen and microbial contamination management in micropropagation. Edit. A.C. Cassells, Kluwer Academic Publishers, Dordrecht, Boston, London, 370 p.
CHILTON M.D., DRUMMOND M.H., MERLO D.J., SCIAKY D., MONTOYA A.L., GORDON M.R. & NESTER E.W., 1977. Stable incorporation of plasmid DNA into higher plant cells : the molecular basis of crown gall tumorigenesis. Cell 11, 267-271.
DEREUDDRE J., BLANDIN S. & HASSEN N., 1991. Resistance of alginate-coated somatic embryos of carrot (Daucus carota L.) to dessiccation and freezing in liquid nitrogen : 1. effects of preculture. Cryo-Letters, 12, 125-134.
De Verna J.W. & Paterson A.H., 1990. Genetics of Lycopersicon. in : Genetic improvement of tomato. Monographs on theoretical and applied genetics. Vol. 14. Edit. G., Koloo Springer Verlag Berlin, genetics. Vol. 14. Edit. G., Koloo Springer Verlag Berlin, p. 21.
FOOLAD M.R. & CHEN F.Q., 1998. RAPD markers associated with salt tolerance in an interspecific cross of tomato (Lycopersicon esculentum & L. pennellii). Plant Cell Report, 17, 306-312.
FRANCLET A., 1981. Rajeunissement et propagation végétative des ligneux. Annales AFOCEL 1980, 11-40.
FRANCLET A. & FRANCLET-MIRVAUX M.C., 1992. Elimination of topophysis in Sequoia sempervirens clone NP 29 : A model plant useful to progress in understanding the concept of rejuvenation. In : "Mass production technology for genetically improved fast growing forest tree species". Symposium AFOCEL-IUFRO, Bordeaux (France) 1992, AFOCEL (Nangis, France), Vol. 1, pp. 113-125.
HOKKANEN H.M.T., 1998. Ecological impact of transgenic, insect resistant crops. In : Génie génétique : perspectives, inconnues et risques. Les applications en agriculture et dans l'alimentation. Colloque international, Groupe des Verts au Parlement Européen Bruxelles, 5-6 mars 1998, 8 p.
Grosser J.W., 1990. Citrus rootstock improvement by cell fusion. Citrus and vegetable Magazine, 9, 28-32.
HOLLAND M.A. & POLACCO J.C., 1994. PPFMs and other covert contaminants : is there more to plant physiology than just plant ? Ann. Rev. Pl. Physiol. Plant Mol. Biol. 45, 197-209.
JAIN S.M., SHAHIN E.A. & SAM SUN, 1988. Interspecific prot S.M., SHAHIN E.A. & SAM SUN, 1988. Interspecific protoplast fusion for the transfer of atrazine resistance from Solanum nigrum to tomato (Lycopersicon esculentum L.). Plant Cell Tissue Organ Culture 12, 189-192.
KLING J., 1996. Could transgenic supercrops one day breed superweeds? Science, 274, 180-181.
LEIFERT C. & WOODWARD S., 1997. Laboratory contamination management ; the requirement for microbiological quality assurance. In : Pathogen and microbial contamination management in micropropagation. Edit. A.C.Cassells, Kluwer Academic Publishers, Dordrecht, Boston, London, pp. 237-244.
LITZ R.E., MATHEWS V.H., MOON P.A., Pliego-Alfaro F., Yurgalevitch C. & DEWALD S.G., 1993. Somatic embryos of mango (Mangifera indica L.). In : Synseeds. Application of synthetic seeds to crop improvement. Edit. K. Redenbaugh, CRC press, Boca Raton, Ann Arbor, London, Tokyo, pp. 409-425.
MELLOR F.C. & STACE-SMITH R., 1977. Virus-free potatoes by tissue culture. In : Applied and fundamental aspects of plant cell, tissue and organ cultures. Edit. J. Reinert and Y.P.S. Bajaj, Springer-Verlag, Berlin, pp. 616-635.
MONTEUUIS O., 1989. Méristèmes, vieillissement et clonage d'arbres forestiers. Ann. Rech. Sylvicoles-1988, AFOCEL (Nangis, France), pp. 7-53.
MOREL G. & MARTIN C., 1952. Guérison de dahlias atteints d'une maladie à virus. C.R. Acad. Sci. 235, 1324-1325.
MOSELLA Lagrave; virus. C.R. Acad. Sci. 235, 1324-1325.
MOSELLA L.C., SIGNORET P.A. & JONARD R., 1980. Sur la mise au point de techniques de microgreffage d'apex en vue de l'élimination de deux types de particules virales chez le pêcher (Prunus persica Batsch). C.R. Acad. Sci. 290, 287-290.
NAVARRO L. & JUAREZ J., 1977. Tissue culture techniques used in Spain to recover virus-free Citrus plants. Acta Hortic. 78, 425-453.
PALMA B., VOGT G.F. & NEVILLE P., 1997. La microgreffe, une solution pour la multiplication in vitro de l'Acacia senegal L. Ann. Sci. For. 54, 203-210.
PIERIK R.L.M., 1991. Commercial micropropagation in Western Europe and Israel. In : Micropropagation of horticultural crops. Edit. P.C. Debergh and R.H. Zimmerman, Kluwer Academic Publishers, Dordrecht, pp. 157-165.
RedenbaUgh K., 1993. Synseeds. Applications of synthetic seeds to crop improvement. CRC Press, Boca Raton, Ann Arbor, London, Tokyo, 481 p.
RedenbaUgh K., FUJII J., Slade, D., Viss, P., & KosSLER, M., 1991. Artificial seeds encapsulated somatic embryos. in : Biotechnology in agriculture and forestry, Vol. 17, High-Tech and Micropropagation 1, Edit. Bajaj, Y.P.S., Springer-Verlag, Berlin, pp. 395-416.
REISH B., 1983. Genetic variability in regenerated plants. In : Handbook of plant cell culture, vol. 1,. Edit. W.R. Sharp, D.A. Evans, P.V. Ammirato, Y. Yamada. Macmillan Publishing Company, New York, pp 748-76 Yamada. Macmillan Publishing Company, New York, pp 748-769.
RIVAL A., BERLENC F.A., MORCILLO F., TREGEAR J., VERDEIL J.L. & DUVAL Y., 1997. Scaling up in vitro clonal propagation through somatic embryogenesis : the case of oil palm (Elaeis guineensis Jacq.). Plant Tissue Culture and Biotechnology, 3,2, 74-83.
SEIBERT M., 1976. Shoot initiation from carnation shoot apices frozen to -196C. Science, 191, 1178-1179.
SEMAL J. & LEPOIVRE Ph., 1992. Biotechnologie et Agriculture: impact et perspectives. Cahiers Agriculteurs, 1,3, 153-162.
SIBI M., 1990. Genetic bases of variation from in vitro tissue culture. In : Somaclonal variation in crop improvement. Edit. Y.P.S. Bajaj, Springer Verlag Berlin, pp. 112-133.
Smith D.R., 1997. The role of in vitro methods in pine plantation establishment : the lesson from New Zealand. Plant Tissue Culture and Biotechnology, 3,2, 63-73.
SMITH C.J.S., WATSON C.F., RAY J., BIRD C.R., MORRIS P.C., SCHUCH W. & GRIERSON D., 1988. Antisense RNA inhibition of polygalacturonase gene expression in transgenic tomatoes. Nature 334, 724-726.
STONE, O.M., 1963. Factors effecting the growth of carnation plants from shoot apices. Ann. appl. Biol. 52, 199-209.
TANKSLEY S.D., MEDINA-FILHO & RICK C.M., 1981. The effect of isozyme selection on metric characters in an interspecific backcross of tomato-basis of an early screening procedure. Their Appl. Genet. 60, 291-29 an early screening procedure. Their Appl. Genet. 60, 291-296.
WANG P.J., 1977. Regeneration of virus-free potato from tissue culture. In : Plant tissue culture and its biotechnological application. Edit. Barz W., Reinhard E. and Zenk M.H., Springer Verlag, Berlin, Hedelberg, New York, pp. 386-391.
WANG P.J. & CHARLES A., 1991. Micropropagation through meristem culture. In : Biotechnology in Agriculture and Forestry, 17, High Tech and micropropagation I. Edit. Y.P.S. Bajaj, Springer-Verlag, Berlin, pp. 32-52.
ZIMMERMAN R. Commercial micropropagation laboratories in the United States. In : "Pathogen and microbial contamination management in micropropagation". Edit. A.C. Cassells, kluwen Academic Publishers, pp. 39-44.
ZIV M., 1990. Morphogenesis of Gladiolus buds in bioreactors.
Implication for scaled-up propagation of geophytes. In : Progress
in plant cellular and molecular biology. Proceedings of the VIIth
Internl. Congress on plant tissue and cell culture, Amsterdam,
June, 27-29th, Edit. H.J.J. Nijkamp, L.H.W. Van der Plas and J.
Van Aartrijk, Kluwer Academic Publischers, Dordrecht, pp. 119-124.