Breeding for improved performance under environmental stresses involves activities which accumulate favourable alleles (different forms of a gene) which contribute to stress tolerance. Biotechnological contributions to crop adaptation to climate change do not only, or even mainly, concern the placement into the crop of one or more genes from an organism with which the crop could not normally breed (i.e. genetically modified crops). Biotechnological tools focus on providing the ability to directly detect and transfer genes of interest from other plant lines or organisms into the crop of interest without the continuing need to use the appearance or stress response of the plant (its phenotype) as a proxy for the presence of that gene. Phenotyping (measurement of the response of a plant line in a given environment) is still a vital part of the selection process but when a genetic region shown to be conferring an adaptive advantage has been identified, it can be transferred (even across species barriers) much more rapidly and efficiently than has been possible up to now.
Superior genes or alleles can often be found within other lines or races of the same crop and their efficient accumulation can be greatly speeded by molecular breeding where the presence of desirable genes or alleles can be directly and immediately identified, even in seeds or very young plants not exposed to the stress in question. More complex are marker-assisted backcrossing (MAB) and marker-assisted recurrent selection (MARS) techniques, allowing exactly identified pieces of DNA (individual alleles, genes or qualitative trait loci (QTLs) to be included in the desired plant line while minimising the transfer of other, less desirable, genes. Whole genome sequences are now available for soybean, maize, rice, sorghum and recently potato and high throughput ‘next-generation sequencing’ means that this process is rapidly accelerating, allowing the sequencing of large and complex genomes of crops such as wheat and barley. Desirable genetic loci identified in one genome can be quickly searched for in others (more detailed definitation of the terms are given in Table 1).
Table 1: Terms related to biotechnology
|Genetic Engineering (GE): Manipulation of genetic material of an organisms using recombinant DNA technology|
|Transgenic or Genetically Modified Organism (GMO): A plant produced by GE where the inserted genes come from a different species|
|Cisgenic: A GMO plant produced by GE where the incorporated genes/alleles are from other varieties of the same species|
|Marker-assisted backcrossing (MAB): Marker-assisted selection to introgress precisely the donor segment into the breeding line followed by marker-assisted backcrossing to recover the desired parent genome|
|Marker-assisted recurrent selection (MARS): Marker-assisted crossing scheme using multiple parent lines aimed at producing superior genotypes though capturing the effects of various genomic fragments with desirable QTLs, from the different parent lines. (Not possible with conventional breeding)|
|Molecular breeding (MB): The use of genetic tools such as DNA markers in traditional breeding (increases selection efficiency and reduces the length of breeding cycles)|
|Quantitative trail loci (QTLs): regions of the genome associated with complex quantitative trails governed by several large-effect and some smaller-effect genes. Transferring whole QTLs can help produce stable trait transfers.|
Source: based on Varshney et al, 2011
Genes that confer a measure of abiotic stress tolerance can be obtained from germbank collections, wild relatives of the crop, or from other organisms known to perform well under water deficit/excess or high salinity or temperatures. Boxes 4.31 and 4.32 give examples of the identification and integration of drought tolerance trails into two major global staples, rice and maize. Careful use of the molecular breeding tools described above have enabled a three to five-fold increase in rice yields and a five-fold increase in the yields of the best maize lines. These materials are being actively disseminated into breeding lines across Asia and Africa now and, just as importantly, they have been passed to commercial seed companies for the production of superior hybrid lines.
There is a great deal of activity within the major biotechnology life sciences companies and the agricultural research institutes and academic institutions on transgenic research for drought-prone environments (Ortiz et al, 2007 and Varshney et al, 2011). In the developing world, China, Brazil and India are clear leaders. The international donor community is supporting work in this area through the Consultative Group on International Agricultural Research (CGIAR) and in particular through the Generation Challenge Programme in which partners from the CGIAR institutions such as the International Rice Research Centre (IRRI) or the International Maize and Wheat Research Centre (CIMMYT) work with leading ARI and ARS institutes in developing countries. In addition to the plant lines coming out of these collaborations, the Genomics and Integrated Breeding Platform (GIBS) being developed by this programme will provide the technical suite of tools to enable any breeder to utilise these new technologies on-line. In addition, ‘communities of practice’ are under construction to provide the peer support which will be required for their efficient utilisation.
Much of the initial work has been with the plant genetics ‘guinea-pig’ Arabidopsis, however, benefits for field crops are rapidly emerging. For example the HRD gene in transgenic rice has improved water use efficiency and the ratio of biomass produced to the amount of water used, through enhanced photosynthesis and reduced transpiration (Karaba et al, 2007). Correlation of drought tolerance with root architecture (spread, depth and volume) has been examined in cowpea (South Africa., West Africa and India), rice (India) and beans (Central and South America). Other modifications are further from commercialisation Table 2.
Table 2: Biotechnology Products Showing Longer-term Promise for Adaptation to Climate Change
|Drought tolerant rice||HARDY (HRD) gene from Arabidopsis, reducing transpiration and enhancing photosynthetic assimilation||Reduced transpiration, increasing biomass/water use ratio, adaptive increase of root mass under water stress||Karaba et al, 2007|
|Drought tolerant tobacco (model)||Delayed drought-induced leaf senescence||Retained water content and photosynthesis resulting in minimal yield loss under drought (30% normal water requirements).||Rivero et al, 2007|
|Drought tolerant maize||Expression of glutamate dehydrogenase (gdhA) gene from E.coli.||Germination and grain biomass production under drought increased.|
Lightfoot et al, 2007Castiglioni et al, 2008
|Drought tolerant maize||Enhanced expression of phosphatidylinositol-specific phospholipase by ZmNF-YB2 reducing stomatal conductance and so leaf temperature and water loss||Grain yield increases through reduced wilting and maintenance of photosynthesis under drought||Nelson et al, 2007|
|Salt tolerant rice||A QTL (Saltol) associated with drought resistance||Allows close to normal yield under high salinity situations (Bangladesh)||IRRI annual report, 2009|
If ‘in the seed’ solutions can be delivered to farmers which mitigate the harmful effects of climate change there is great potential for maintaining food and fibre production in a degrading environment and for expanding the farmable area into currently marginal environments. This is not to imply that environmental remediation is unnecessary but it helps to provide a buffer on its urgency. The major benefit from molecular breeding to date is the speed with which multiple traits can be identified, captured and incorporated into plants and then be tested for stability and efficacy. This has increased exponentially in the last 15 to 20 years. Genetic engineering technologies allow us to utilise capacities outside the range normally available in our crop plants. Because gene insertions can now be targeted and checked in ways that were not previously possible, we can have a higher confidence in the safety of the new plant lines and can be sure that other functional plant genes have not been disrupted by the insertion. We can expect similar scale benefits from a whole range of molecular breeding (including genetic engineering) products in the short to medium-term future.
Drought and flooding are unpredictable. Ensuring that the developed plants perform well in a wide range of environmental conditions is a challenge that will require even deeper understanding of the molecular basis of responses to stress. As with other areas of modern technology, molecular breeding is becoming more and more complex and inaccessible as a science for those of modest means. The financial investment needed for efficient molecular breeding is high and companies are recouping their investment through higher seed prices and selling their material only as hybrids, effectively preventing replanting any of the seeds produced. On one hand this ensures quality control in seed purity, on the other hand it creates low autonomy on the part of the farmer. Concerns over loss of crop biodiverisity have had a mixed history. India for example now has more than 750 registered Bt cotton varieties, around the same as were available nine years ago when the genetic modified Bt trait was introduced, but there is no doubt that these varieties have a narrower genetic base than formally – Gossypium arboreum previously covered some 40 per cent of the cotton area ─ and of those areas which were G.hirsutum, 60 per cent was in a range of varieties and only 50 per cent in hybrids. Now over 95 per cent of the country is growing a limited range of G.hirsutum hybrids. This concentration of advanced breeding material seems likely to continue, if only because the manpower and regulatory costs of producing and releasing substantially novel plant lines requires large markets to support the investment marginalising niche market varieties and land races.
There have been very different farmer cost experiences with existing bioengineered crops globally depending on the regulatory systems in place. Where private seed companies have been able to monopolise the market they have capitalised it with either famer agreements forbidding seed saving and imposing a technology fee in addition to the increased seed cost (for example, in the USA and Australia). Where this was impractical, such as in India, the seed sector forced a monopoly through the production of only hybrid seeds. Prices began at six to ten times that of non-biotech seed but gradually declined to three to four times because of court requirements and increasing competition. China enforced competition from the beginning and had less seed price inflation. However, even in countries where seed prices were very high, the average balance of financial benefit still rested with the farmer. After a brief period of adaptation around 60 to 80 per cent of the financial benefit of the seed tends to go the farmer and about 10 per cent to the technology developer, with the balance going to the supply chain. Many of the biotechnology responses to climate change are public sector developments intended for free or ‘at cost’ dissemination and are aimed at subsistence farmers with very limited ability to pay for improved inputs, particularly in the marginal environments likely to be first affected by climate change. However, the reality of the global seed distribution system make it likely that the commercial sector will be the most efficient disseminator of seed and the guardian of their purity, provided they are given some proprietary rights. Prices will then be set based on the average advantages to farmers, as in other sectors of the marketplace.
There are rather few publications on the economic impacts of biotechnology products on climate change adaptation. Alpuerto et al (2009) undertook an analysis of salinity and phosphorous tolerance in rice where the cumulative benefit to Bangladeshi farmers using marker assisted breeding rather than conventional breeding are forecast to be US$ 800 million for salinity tolerance and US$ 450 million for Phosphorus deficiency if conventional breeding takes 5 years longer than MAB, which is a conservative estimate. The medium term impact of the work described here and the many other products which are slightly less advanced but are in the pipeline, is expected to be dramatic.
If ‘in the seed’ solutions are relatively light in terms of requisite farmer or extension service knowledge requirements. But, as can be seen from Box A, like any technology advance, an enabling environment is necessary for benefit maximisation and can sometimes be generated by it. Over-expectation of bioengineered crops has been a problem internationally, for which the seed industry must take some responsibility. Given the seed price implications, it is important the seed industry and extension services give farmers an accurate picture of the extent to which such crops can accommodate adverse environmental conditions and what growth and yield can be expected in local environments.
The limited access of public and developing country breeding programmes to these technologies is being addressed by the Generation Challenge Programme’s molecular breeding platform (GIBS). This is a brave attempt to put these high-tech tools in the hands of small-scale breeders.
The global crop breeding community has found it more difficult than expected to use the outputs of molecular breeding research in its various forms for the rapid development of improved cops for poorer farmers. Even within crop species, genome structure and gene orders have proved to be more variable than expected. The prevalence of polygenic traits with strong genetics/environment interactions have been more marked than was foreseen, making successful expression of the valued trait after intra or inter-specific transfer more elusive than had been hoped. This is slowing (and deepening) research by all organisations (including commercial companies) in this area.
Molecular breeding is not proving to be either faster or cheaper than conventional breeding, though its worth has already been demonstrated for simple traits. The generally polygenic nature of the traits necessary for the amelioration of climate change-induced shifts in the environment, makes this more difficult still. However, unlike conventional breeding, the knowledge gained with molecular breeding is incremental and will enable much more effective, productive, targeted and rapid crop development over time. Trait development is expensive and high quality seed lines are costly to maintain. As with other sections of the seed sector, effective variety/hybrid development and dissemination will depend on the value capture mechanisms available to the players in the seed chain. Properly designed, there is no reason why these mechanisms should delay the delivery of significant benefits to farmers. In the specific area of GMOs we are likely to see continued extremely high costs of regulation, significantly delaying plant provision and significantly increasing costs to farmers and pushing ownerships rights strongly into the hands of larger, often multi-national, companies. It is probably true that this regulatory burden has led to most genetically modified crop dissemination in the developing world starting in the informal sector and products only receiving regulatory approval in retrospect. This is not desirable but seems likely to continue and expand while current regulatory regimes are in place.
These yield stabilising or enhancing technologies are likely to be taken up very quickly by farmers, most particularly where heat/drought/salinity is clearly moving against them over a series of seasons. Seed companies will not be slow to exploit the opportunities offered though it is likely that many of the best parental lines will emerge from public sector programmes.
Castiglioni, P., et al. (2008) Bacterial RNA chaperones confer abiotic stress resistance in plants and improved grain yield in maize under water limiting conditions. Plant Physiology 147: 446-455
Karaba, A, S. Dixit, R. Greco, K.R. Trijatmiko, N. Marsch-Martinez, A. Krishnan, K.N. Nataraja, M. Udayakumar, and A. Pereira (2007) Improvement of water use efficiency in rice by expression of HARDY and Arabidopsis drought and salt tolerance gene. Proceedings of the National Academy of Sciences (USA) 104: 15270-15275
Lightfoot, D.A,, R. Mungur, R. Ameziane, S. Nolte, L. Long, K. Bernhard, A. Colter, K. Jones, M.J. Iqbal, E. Varsa, and B. Young (2007) Improved drought tolerance of transgenic maize Zea mays plants that express the glutamate dehydrogenase gene (gdh4) of E.coli. Euphytica 156: 103-116
Nelson, D.E. et al (2007) Plant nuclear factor Y (NF-Y) B subunits confer drought tolerance and lead to improved corn yields on water limited acres. Proceedings of the National Academy of Sciences (USA) 104: 16400-16455
Ortiz, R (2008) Crop genetic engineering under global climate change. Annals of the Arid Zone 47(3&4): 1-12
Ortiz, R., M. Iwanaga, M. P. Reynolds, H. Wu, and J. Crouch (2007). Overview on crop genetic engineering for drought prone environments. Journal of Semi-Arid Tropical Agricultural Research 4 http://www.icrisat.org/jornal/SpecialProject/sp3.pdf
Rivero, R.M., M. Kojima, A. Gepstein, A., H. Sakakibara, R. Mittler, S. Gepstein and E. Blumwald (2007). Deayed leaf senescence induces extreme drought tolerance in a flowering plant. Proceedings of the National Academy of Sciences (USA) 104: 19631-19636
Varshney, R.K., K.C. Bansal, P.K. Aggarwal, S. Datta and P.Q. Craufurd (2011) Agricultural biotechnology for crop improvement in a variable climate: hope or hype? Trends in Plant Science 16(7): 363-371