Published in Crop Sci. 44:1913-1914 (2004).
© 2004 Crop Science Society of America
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SYMPOSIUM ON GENOMICS AND PLANT BREEDING: THE EXPERIENCE OF THE INITIATIVE FOR FUTURE AGRICULTURAL AND FOOD SYSTEMS
Plant Breeding Requirements for Applied Molecular Biology
Major M. Goodman*
Dep. of Crop Science, North Carolina State Univ., Raleigh, NC 27695
* Corresponding author (maize_resources{at}ncsu.edu)
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INTRODUCTION
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PLANT BREEDING is unlikely to be radically altered by genetic engineering despite progress in genomics. New traits will ultimately be added to today's breeding goals, but most are likely to require several decades of development. Many have decided that the future of plant breeding lies in genomics, relying on claims that molecular genetics has revolutionized the time frame for product development. "Seldom has it been pointed out that it is going to take as long to breed a molecular engineering gene into a successful cultivar as it takes for a natural gene" (Bingham, 1983, p. 223). Additionally, claims often suggest simple solutions to very complex problems ["Agricultural biotechnology is already having an impact" (on starvation!); Theil, 2001]. Such claims are often made with little knowledge of the problems of selecting and testing germplasm, genotype x environment interactions, or even epistasis. These claims are often accepted by management that employs breeders who certainly know that such "quick solutions" will not reach farmers' fields for well over a decade. "The public must be cautioned that the simplest advances take, on average, 10 yr from inception of breeding effort to placement on the farm in quantity" (Duvick, 1982, p. 583). It is simply untrue that a new transgenic cultivar can be routinely created, tested, and deployed within a decade (Goodman and Carson, 2000).
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Transgene Utilization
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Insecticidal Bacillus thuringiensis (Bt) was used by the 1950s. The first gene encoding the Bt toxin was cloned by Schnepf and Whiteley (1981). Bt gene regulation was known by 1986 (Whiteley et al., 1987). Bt was transformed into maize (Zea mays L.) in 1990 (Koziel et al., 1993). Bt hybrids were first sold in 1997. Because Bt was a well-known entity with a long history of use as an "organic" insecticide, it was relatively straightforward for regulatory agencies to assess for its initial use as a transgene, compared with less well-known genes that genomics research may make available.
Even so, its development into a commercial product took 16 yr.
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Integration of Breeding with Plant Molecular Biology
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Breeding progress continues to increase yield at a rate of 1 to 2% per year, with additional gains made for disease resistance, maturity, standability, and production efficiency. Virtually all gains are due to utilization of polygenic factors not readily handled by currently available molecular procedures. Molecular genetics will not add much to routine breeding practices until this is overcome. Is marker-assisted selection (MAS) an alternative? Studies by Beavis (1994), Openshaw and Frascaroli (1997), and Bernardo (2001) strongly suggest that MAS is only effective under specific circumstances. For those interested in the discouraging details, see Goodman and Carson (2000) and Melchinger (2003). Currently in place are several simply-inherited qualitative traits such as Bt-insect control, herbicide resistances, virus resistances, and new sources of the equivalent of cytoplasmic male sterility. What is needed by plant breeders? Traits that plant breeders can only manipulate with difficulty or traits currently unavailable. These include traits like drought tolerance, fungal-toxin (aflatoxins, fumonisins) resistance, salt tolerance, heat tolerance, and general environmental stability.
It is unlikely that the minimal 15-yr lag time between gene discovery and seed sales to farmers can be reduced, but politics could effectively increase it, especially in Europe. Thus, new developments in molecular genetics must promise a 20 to 30% improvement in yield or offer a useful, novel trait without reducing yield or they are unlikely to survive the 15+ yr development curve. In addition, realism needs to accompany proposed modifications in seed characteristics. There are clear benefits to be gained from eliminating unhealthy or quality-degrading oils from soybean [Glycine max (L.) Merr.] or palm (Elaeis guineensis Jacq.). It is not clear that increasing oil or protein content in maize will be beneficial. No crop is an island unto itself. Food or rations containing oil or protein from legumes, starches from grains, and vitamins from vegetables probably make more economic sense than maize with 10% oil, a completely balanced amino acid ratio, and additional vitamins.
The several steps required to move a sequenced gene into a commercial product were outlined by Goodman and Carson (2000) and Gepts (2002). Initial estimated costs of this were as low as $5 million; current estimates are in excess of $60 million. These compare with the generally accepted, approximate cost of $1 million to develop a useful, conventionally bred inbred line. Thus, commercial development of a single gene is now roughly 50 times as costly as the development of a commercial inbred by conventional breeding. This is a formidable barrier, as Bt seems to have been sold at just about the break-even point for the farmer, at about 30% of seed cost (Duffy, 2001). It is unlikely that any combination of transgenes now on the horizon could greatly increase this premium while farmers are selling maize at the low price of $2.50 per bushel.
Any molecularly engineered trait of clear economic use will be rapidly utilized by plant breeders. What is lacking at present is an array of useful transgenic traits. The easy and obvious ones have been implemented. At the moment, the pipeline of molecularly engineered traits appears to be largely empty. [Bt for maize rootworms (Diabrotica spp.) has recently become available, but it has few companions.] Indeed, the question can be asked, does the pipeline exist or do we just have random bits of pipe strewn about, with rather little organization?
There is little doubt that plants (and animals) will be used to produce certain chemicals and pharmaceticals, but this is apt to be on a horticultural scale, rather than a broad-based agricultural effort. There is considerable need for fungal and bacterial protection of crop plants, but progress has been slow. Worldwide, the greatest problem that needs to be solved for most food- and feed-crops is postharvest protection against insects and vermin. That would solve far more problems than adding carotene to rice or lysine to maize.
Received for publication July 23, 2003.
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REFERENCES
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- Beavis, W.D. 1994. The power and deceit of QTL experiments: Lessons from comparative QTL studies. Annu. Corn Sorghum Research Conf. Proc. 49:250–266.
- Bernardo, R. 2001. What if we knew all the genes for a quantitative trait in hybrid crops? Crop Sci. 41:1–4.[Abstract/Free Full Text]
- Bingham, T. 1983. Molecular engineering vs plant breeding. Plant Mol. Biol. 2:222–224.
- Duffy, M. 2001. Who benefits from biotechnology? Annual Corn Sorghum Research Conference Proc. 56, http://www.leopold.iastate.edu/pubs/speech/files/120501-who_benefits_from_biotechnology.pdf; verified 6 July 2004.
- Duvick, D.N. 1982. Improved conventional strategies and methods for selection and utilization of germplasm. p. 577–584. In L.W. Schemilt (ed.) Chemistry and world food supplies: The new frontiers. Pergamon Press, Oxford, UK.
- Gepts, P. 2002. A comparison between crop domestication, classical plant breeding, and genetic engineering. Crop Sci. 42:1780–1790.[Abstract/Free Full Text]
- Goodman, M.M., and M.L. Carson. 2000. Reality vs. myth: Corn breeding, exotics, and genetic engineering. Annu. Corn Sorghum Research Conf. Proc. 55:149–172.
- Koziel, T.M., G.L. Beland, C. Bowman, N.B. Carozzi, R. Crenshaw, L. Crossland et al. 1993. Field performance of elite transgenic maize plants expressing an insecticidal protein derived from Bacillus thuringiensis. Bio/Technology 11:194–200.
- Melchinger, A.E. 2003. Lessons from large QTL mapping experiments in maize. Annual Corn and Sorghum Research Conf. Proc. [CD-Rom]. 58:512–532.
- Openshaw, S., and E. Frascaroli. 1997. QTL detection and marker-assisted selection for complex traits in maize. Annu. Corn Sorghum Research Conf. Proc. 52:44–53.
- Schnepf, H.E., and H.R. Whiteley. 1981. Cloning and expression of the Bacillus thuringiensis crystal protein gene in Escherichia coli. Proc. Natl. Acad. Sci. USA 78:2893–2897.[Abstract/Free Full Text]
- Theil, K.A. 2001. Kernels of truth. Forbes ASAP. Feb. 19. p. 113–115.
- Whiteley, H.R., H.E. Schnepf, K. Tomczak, and J.C. Lara. 1987. Structure and regulation of the crystal protein gene of Bacillus thuringiensis. p. 13–27. In K. Maramorosch (ed.) Biotechnology in invertebrate pathology and cell culture. Academic Press, San Diego.
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TOP
INTRODUCTION
Transgene Utilization
