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watching extracts of a particular film. We now know that there are immediate effects on both mood and thoughts, and that some messages work better than others in this regard. But it raises many other questions. Would the emotional responses be sustained over longer periods of time, and how might this translate into changes in people’s behaviour? Can films like this produce such a strong response that they actually make a real difference to how we live our lives? These are important questions with potentially very significant implications for the future of the planet and for us all.

In the meantime, educators, policymakers and others who are trying to communicate climate change to a broad audience could learn from our findings (and Gore’s film), and employ some of

Gore’s more successful strategies to good effect. These might include humanizing the impacts of climate change, with vivid, concrete, emotional images, as was done with great effect in the ‘rising sea levels’ clip, and perhaps by focusing more on domestic emissions, to avoid some of the negative responses generated by showing other countries polluting. Although climate change is a truly global issue, constructing messages that focus on what distant others are doing wrong may, psychologically, let viewers in the rich world off the hook, which is not in anyone’s interest.

There is plenty of scope for improvement — after all, Gore’s film did not produce the kind of changes that he was hoping for. The question still remains as to how to build effectively on the immediate psychological effects induced by the best bits of his

film, so that viewers do actually change their behaviour. ❐

Geoffrey Beattie is a professor of psychology and a professorial research fellow in the Sustainable Consumption Institute at the University of Manchester, Oxford Road, Manchester M13 9PL, UK. e-mail: geoff.beattie@manchester.ac.uk

References1. Damasio, A. R. Descartes’ Error: Emotion, Reason, and the Human

Brain (Putnam Publishing, 1994).2. Weber, E. U. Climatic Change 77, 103–120 (2006).3 Tollefson, J. Nature Clim. Change 1, 385 (2011).4. Beattie, G., Sale, L. & McGuire, L. Semiotica 187, 105–125 (2011). 5. Kellstedt, P. M., Zahran, S. & Vedlitz, A. Risk Anal.

28, 113–126 (2008). 6. Matthews, G., Jones, D. M. & Chamberlain, G. A. Brit. J. Psychol.

81, 17–42 (1990).7. Lee, V. & Beattie, G. Semiotica 120, 39–92 (1998).8. Lee, V. & Beattie, G. Semiotica 130, 1–81 (2000).

Published online: 16 October 2011

COMMENTARY:

A walk on the wild sideLuigi Guarino and David B. Lobell

Feeding a growing population in a hotter world will require exploiting a far broader range of crop diversity than now — and that means valuing wild genes.

Over much of the world, the growing season of 2050 will probably be warmer than the hottest of recent

years1, with more variable rainfall2. If we continue to grow the same crops in the same way, climate change will contribute to yield declines in many places3. With potentially less food to feed more people, we have no choice but to adapt agriculture to the new conditions.

To some extent, adaptation can be done by moving crops to more favourable areas and by agronomic tweaks. But that will almost certainly not be enough. We will have to give crops a genetic helping hand, infusing them with new genes to allow them to better cope with new climates, and the new pests and diseases they will bring. Where are these genes going to come from?

Some of them could come from completely unrelated organisms, to be spliced into their new genomic homes using advanced biotechnologies4. However, there is significant public resistance to that strategy, and it is still unclear how effective genetically modified crops are at coping with heat and drought. We cannot risk putting all our eggs in that basket.

Another source of genes for crop improvement are traditional heirloom varieties, often called landraces, which are still grown by subsistence farmers in many parts of the world, although they are fast disappearing. Large collections of their seeds have been made over the years, creating genebanks that are scoured by plant breeders searching for crop diversity, and which helped spur the Green Revolution in agriculture from the late 1960s.

But there’s a limit to the diversity found in domesticated species, imposed by domestication itself. Cultivated species usually contain a fraction of the genetic diversity found in their closest wild relatives — a legacy of the ‘domestication bottleneck’. Ancient farmers selected relatively few plants from the progenitors of modern crops, in a limited number of places. Although there has been continuous gene flow between crops and their wild relatives where they coexist, a lot of genetic diversity has been lost as agriculture has developed.

We know that the ‘lost’ genetic diversity includes genes for resistance to high temperatures and drought, and to pests and diseases, as well as taste and nutritional

composition, and even yield. If there was ever a time to go back and reclaim this diversity, that time is now. In fact, it is already being used more than many people realize. For instance, there is probably no widely grown rice cultivar that does not have some genes obtained by breeders from its wild relatives. But we could be making much more effective, and systematic, use of the reservoir of diversity our Neolithic ancestors left behind.

In many cases we are not storing enough of this diversity in genebanks, where it is easily accessible to breeders. Global genebank holdings of crop wild relatives are a small proportion of the total diversity (4–5% for food legumes and cereals, for example), and some species are lacking altogether5. Furthermore, the material held in genebanks is not necessarily available for use, either because the quality of the seed has deteriorated or quantities are limited, or for political reasons. In addition, many populations of crop wild relatives that still exist in the field are threatened by changes in land use and climate.

Much of the diversity of crop wild relatives that is available in genebanks is neglected,

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because most crop-breeding programmes are generally not set up to best use it. Breeders, particularly in the private sector, are rewarded for releasing new varieties quickly, and wild relatives are viewed as too unwieldy to use with sufficient ease and speed. As one breeder has put it, “it’s a bit like crossing a house cat with a wildcat. You don’t automatically get a big docile pussycat. What you get is a lot of wildness that you probably don’t want lying on your sofa.”

For many crops, the neglect of wild relatives is more simply the result of an overall dearth of breeding activity. Incredibly, crops that support millions of people are often themselves only supported by a few breeders. For example, there are only about half-a-dozen banana breeders in the whole world.

What would a system that successfully exploits the unique opportunities presented by crop wild relatives look like? It would begin with a systematic global effort to secure their genetic diversity, a goal which is helped by the recently announced initiative by the Global Crop Diversity Trust in partnership with the Millennium Seed Bank at Kew Gardens, funded by the Norwegian government, to identify and fill gaps in existing collections, from fruits to grains6. It will not be easy. These species often grow in isolated, inaccessible and dangerous places. They are difficult to conserve in genebanks, as procedures for the optimal storage and regeneration of their seeds are mostly unknown.

Once collected and conserved, the next step is to make the diversity of wild relatives as easy to use as possible. This involves ‘pre-breeding’ or ‘germplasm enhancement’, in which modern varieties are crossed with different wild relatives, followed by repeated back-crosses to the modern parents, while the performance and genetics of the resulting progenies are monitored. It allows researchers to identify specific useful genes and to broaden the genetic base of the crop.

Pre-breeding does not produce new varieties, but it does turn up intermediate products that breeders in the private and public sectors find easier to use. It has been a mainstay of the work at public

agricultural research institutions, such as the International Rice Research Institute and the International Maize and Wheat Improvement Center, for many years. However, funding for public sector plant breeding has been declining over the past decade and funds for pre-breeding have suffered disproportionately. The above-mentioned Norway-funded project includes support for such work, too, aside from collecting. But a lot more needs to be done.

We do have a solid foundation to build on. Since it came into force in 2004, there is a political infrastructure in the International Treaty for Plant Genetic Resources for Food and Agriculture that can smooth the way for international collaboration in genetic resources collection and research, at least for the 127 countries that have ratified it. Through the burgeoning global online portal to the contents of genebanks, called Genesys, and other biodiversity information systems (such as the Global Biodiversity Information Facility) we have a better idea of the distribution of diversity worldwide, and can use geographic information systems to analyse genebank and herbarium data to identify potential places and times to collect seed samples7. Places such as the Millennium Seed Bank at Kew and the US Department of Agriculture’s National Center for Genetic Resources Preservation at Fort Collins are doing the necessary seed-storage and germination research to develop best practices for conservation.

However, making progress will require both the political will to really implement the treaty, by enacting any necessary national legislation, and technical changes in the process of genetic resources management. In particular, conservationists and breeders must learn the value of working together. Breeders see genebanks as full of too much material that is too time-consuming to use; genebankers all too often see their job as restricted to conscientiously storing seeds for hypothetical future users — users that unfortunately rarely materialize. Genebanks must get better at providing the genetic material and associated data that breeders need in a form they can use; but breeders must also become better at

feeding back their findings and needs to genebanks. And, crucially, there must be increased support for pre-breeding, the part of crop improvement that really only the public sector can do on a significant scale, as it does not result quickly in commercial varieties. Pre-breeding is the link between conservation and use of crop wild relatives, and can serve to energize both. As prices come down, we can begin to use modern high-throughput genomics tools to give impetus to pre-breeding, to identify and separate the genes for the wildness that you don’t want lying on your sofa from the useful ones that hide behind them.

Out of all the raw materials at the breeder’s disposal, the diversity of crop wild relatives has been relatively neglected. In the past it has been difficult to get hold of and awkward to use, but we know how to change that, and have begun to do so. Even without climate change, it would be a good idea. In a 2 °C-warmer world, we may not have a choice. ❐

Luigi Guarino is at the Global Crop Diversity Trust, c/o Food and Agriculture Organization, Viale delle Terme di Caracalla, 00153 Rome, Italy. David B. Lobell is in the Environmental Earth System Science Department and the Center on Food Security and the Environment, Stanford University, Stanford, Califonia 94305, USA. e-mail: luigi.guarino@croptrust.org

References1. Battisti, D. & Naylor, R. L. Science 323, 240–244 (2009).2. IPCC Climate Change 2007: The Physical Science Basis (eds

Solomon, S. et al.) (Cambridge Univ. Press, 2007).3. Lobell, D. B. et al. Science 319, 607–610 (2008).4. Fedoroff, N. V. et al. Science 327, 833–834 (2010).5. Food and Agriculture Organization The Second Report on the

State of the World’s Plant Genetic Resources (United Nations, 2010); available via http://go.nature.com/5Jf4rn.

6. http://www.croptrust.org/main/index.php?itemid=9087. Ramírez-Villegas, J. et al. PLoS One 5, e13497 (2010).

AcknowledgementsWe are indebted to participants in a meeting on ‘Adapting agriculture to climate change: The role of crop wild relatives’ supported by the Rockefeller Foundation and Kendall Foundation: D. Battisti, D. Bergvinson, D. Brar, C. Fowler, G. Hawtin, R. Hijmans, T. Hodgkin, A. Jarvis, N. Maxted, S. McCouch, R. Naylor, R. Nelson, E. Okogbenin, R. Ortiz, T. Payne, R. Sackville Hamilton, P. Smith and J. Valls. The ideas expressed in this Commentary arose from discussions at this meeting, but any errors are our own.

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