THURSDAY, 12 MARCH 2020The relationship between humans and the plants we cultivate is complex. Plants helped make humans as we are today, and in return we have picked and adapted them to suit our needs by making use of their genetic diversity. Right now, we rely on plant foods to provide about 80% of our calories directly, as well as to feed livestock. In the wake of an expanding human population and climate change, our ability to preserve and foment crop diversity will thus determine the future of human survival. However, changes over the past century have led to an increase in crop production, but a decrease in crop varieties. Once lost, this genetic diversity cannot be recovered. To understand what can be done to ensure a healthy future for humans through resilient crop production, we can look at how this intricate relationship - between humans and our crops - began.
When Africa shifted from dense forest to grassland millions of years ago, hominids adapted and began walking upright, cooperating to hunt and gather food. As they became more intelligent and started using tools, there was an increase in the number of different plants they could eat. There is evidence that 15,000 years ago humans consumed a broad range of plants, including grasses, legumes and pines. About 10,000 years ago, humans started domesticating some of these plants and for the following millennia, continued to place them under selection pressures until they became unrecognisable from the wild plants. A wild plant might be favoured by dispersing its seeds widely, whilst the opposite is true in crops and so they became easy to harvest. Domestication was dependent on the genetic variation of plants, and as Darwin wrote in The Variation of Animals and Plants Under Domestication, “if organic beings had not possessed an inherent tendency to vary, man could have done nothing”.
In the 1960s, the explosive growth of the human population led biologists to predict a mass starvation, believing that population growth would outpace agricultural growth. In the 1968 book The Population Bomb, Paul Ehrlich predicted that over four billion people would die from widespread famine by the 1980s. However, the development of high-yielding crop varieties by research organisations such as the International Maize and Wheat Improvement Centre and the International Rice Research Institute - as well as the increased use of fertilisers, pesticides and modern irrigation techniques - drove a critical increase in agricultural production. Changes in diet followed. With the increased production and the introduction of an international crop trade, anyone could access crops from all over the world. Yet, the world’s reliance on these high-yielding crop varieties has come at a cost: the loss of our crops’ genetic diversity. Farmers have specialised on a narrower number of crops and cultivated fewer traditional crop varieties. For instance, since the commercialisation of apples, the United States of America has lost over 80% of its apple types. India’s cultivated rice varieties have dropped from 100,000 in the twentieth century to less than 10,000 today. This global phenomenon is exacerbated by the fact that the majority of crop production is used to feed livestock which may eat a very narrow diet.
Cultivating and preserving genetically diverse crops can help us mitigate modern problems such as deforestation and, ultimately, climate change. A 2014 meta-analysis by Klümper and Qaim of 147 studies found that the adoption of genetically modified crop varieties led on average to a 22% yield increase. Indeed, cultivating crop varieties such as those resistant to pests can increase the productivity of a field and requires less pesticides, thus altogether reducing the amount of resources and land required for the same crop yield. Using crops of this type could reduce deforestation at no yield cost, and indirectly help us reduce our carbon footprint by ensuring that CO 2 absorbing forests remain intact.
Small-scale plant cultivation may have begun as long as 23,000 years ago, while large scale cultivation is more commonly thought to have begun 12,000 years ago in an area that now comprises Iraq, the Levant, parts of Turkey and Iran.
Whilst we can hope to limit climate change, it is critical that we develop crop varieties that can cope with higher temperatures, reduced water access and other environmental extremes. Environmental conditions are predicted to change faster than crops are able to naturally adapt. One rice variety, ‘scuba,’ released in South East Asia, can withstand complete flooding for two weeks. This was produced by the International Rice Research Institute (IRRI) in the Philippines, using an Indian landrace gene. IRRI stores over 130,000 accessions, or types, of rice which allows them to harness the power of diversity. Nevertheless, breeding new varieties can take up to ten years, making this an urgent task.
Such breeding projects rely on conserved genetic diversity. There are two distinct but complementary agrobiodiversity conservation strategies: in situ and ex situ conservation. In situ conservation involves traditional farmers continuing to grow the crops of their ancestors in the field, while ex situ conservation primarily involves the mammoth task of collecting varieties of crops and related wild species and keeping them frozen and dried in genebanks. These genebanks work at a worldwide scale, providing each country and region with the domestic and international resources they require. The Food and Agriculture Organization of the United Nations estimates that two million unique accessions are conserved ex situ in over 1,750 facilities. In 2004, the Global Crop Diversity Trust (Crop Trust) was established to recognise their importance and permanently support worldwide conservation and supply efforts.
The ultimate back-up genebank is the Svalbard Global Seed Vault, built deep inside the permafrost of Spitsbergen, a Norwegian island. Seeds are only taken out of the Vault in emergencies. One such emergency occurred in 2015 during the Syrian Civil War, when the International Center for Agricultural Research in the Dry Areas (ICARDA) formerly based in Syria was forced to relocate. ICARDA retrieved their seed duplicates from the Vault in order to re-establish their Syria-based collection in Morocco and Lebanon.
The UK is home to the largest and most genetically diverse collection of wild plant species in the world, the Millennium Seed Bank, coordinated by the Royal Botanic Gardens, Kew. Recently, Kew and their partners have been gathering the wild relatives of the world’s 29 major crop species. Not only do these wild plants possess unique traits that could improve crop hardiness, but they are also at risk of going extinct. These missions are currently a race against climate change, with 22% of these wild plants estimated to go extinct by 2055.
Humans are dependent on natural genetic variation, especially in crop breeding, to survive environmental changes. The problem is that we do not know exactly which food security challenges we will face in the future, so we need crop diversity as insurance. The amazing genetic diversity that has evolved over millennia cannot simply be rebuilt by modern genetic modification techniques, and we cannot reverse the loss of genetic diversity from the last decades, but we can preserve what remains. With the establishment of the Crop Trust, the world recognised the need for crop diversity conservation and put this into organised action. However, much more remains to be done. As individuals we can support agrobiodiversity by eating less meat, cooking with diverse ingredients, going to farmers’ markets and looking for seasonal produce, as well as asking supermarkets to stock more varieties of fruit and vegetables. Ultimately, we should care about our food. After all, if we do not take care of our plant species right now, they will not be able to take care of us in the future.
Eleanor McCartney is a genetics PhD student at Pembroke College. Artwork by Eva Pillai.