The curious case of the grass pea
Grass pea (Lathyrus sativus) is one of the 29 key crops that are the focus of the Millennium Seed Bank and the Global Crop Diversity Trust's Crop Wild Relatives project. Sarah Cody discusses the light and dark side of this intriguing and important crop.
Grass pea is a crop with two sides to its personality. Considered both a saviour and a destroyer, in times of famine grass pea is often the only alternative to starvation. Being the hardy plant that it is it can withstand extreme environments, from drought to flooding, and when all other crops fail grass pea will often be the last one left standing. It is easy to cultivate, and is tasty and high in nutritious protein, which makes grass pea a popular crop in south west Asia and the eastern Horn of Africa where it is also grown to feed livestock. Being a member of the legume family, Lathyrus is able to fix nitrogen from the air which means that growing it keeps the soil healthy and well fertilised.
Now, before we make a saint out of the humble grass pea, let us consider some of its more sinister attributes. Eaten in small quantities, grass pea is harmless. However, eating it as a major part of the diet over a three month period can cause permanent paralysis below the knees in adults and brain damage in children, a disorder known as lathyrism. The culprit is a potent neurotoxin called ODAP. This is responsible for the drought and waterlogging tolerance of grass pea but, if taken in large quantities, it brings on the neurological disorder. For example, Ethiopia has seen several lathyrism epidemics in the past 50 years, when hunger overrules the dangers inherent in grass pea consumption. What makes matters worse is that the level of the neurotoxin increases in the crop under conditions of severe water stress which exacerbates the risk of lathyrism at a time when the poorest of the poor have no choice but to rely on the crop for their survival.
According to The Consultative Group on International Agricultural Research (CGIAR) at least 100,000 people in developing countries are believed to suffer from paralysis caused by the neurotoxin. There are a number of ways of preparing grass pea so that it is less harmful, for example, by washing and soaking the grass peas and then discarding the water before cooking or by eating grass pea mixed in with other crops. Both strategies are effective in reducing the risk of lathyrism however in a famine where water and other food sources are scarce, detoxification of grass pea may be harder to implement.
Thanks to the Grasspea
The adverse neurological effects of eating grass pea have been known since prehistoric times. Ancient Indian texts described the disorder and even Hippocrates, the father of modern medicine himself, mentions a neurological disorder caused by eating a Lathyrus seed in 46 B.C. in Greece. Grass pea was served as a famine food during the Spanish War of Independence against Napoleon and below is one of Francisco de Goya’s famous aquatints, Gracias a la Almorta ("Thanks to the Grasspea"). It captures the hardships of the time through its depiction of the poor surviving on grass pea porridge, one of them lying on the floor, already crippled by it. I’m still scratching my head over whether Francisco de Goya was being sarcastic or not when he chose that title – such is the paradox that grass pea presents!
“Why not just abandon the cultivation of this so-called food crop?!” I hear you say. Well, it is not as straightforward as that. Grass pea continues to be the ultimate safety net for subsistence farmers in the poorest parts of the world and provided that consumption does not reach that critical level it is safe and nutritious to eat. Quite simply, grass pea is too important to do away with altogether.
Breeding low toxin varieties
Crop diversity is the key to overcoming this paradox and is the only thing that can put an end to the good cop/bad cop antics of grass pea. The International Centre for Agricultural Research for Dry Areas (ICARDA) is working with Ethiopian breeders to develop cultivars of grass pea with low levels of the neurotoxin ODAP. Toxins found in African and Asian grass pea plants are seven times more toxic than the Middle Eastern varieties. The new ICARDA hybrids have levels of the toxin high enough to keep up the crop’s resilience to drought and flooding, without being damaging to human health. The Centre for Legumes in Mediterranean Agriculture (CLIMA) is also conducting important research in this area and has recently produced a low toxin variety. Hope is on the horizon but much more work needs to be done to produce locally adapted, low toxin varieties and to distribute these to farmers.
Crop Wild Relatives: A source of genetic diversity
The wild relatives of grass pea are an important source of genetic diversity for the cultivation of low toxin varieties. Grass pea is one of the 29 priority crops that are the focus of the Adapting Agriculture to Climate Change project executed by Kew’s Millennium Seed Bank and the Global Crop Diversity Trust. By collecting the wild relatives of crops such as grass pea and making their seeds available to breeders, useful traits such as lower toxicity levels, in the case of Grass pea, and resistance to pests, diseases and environmental stresses can be passed on to crops, making them more resilient and better equipped to deal with climate change. The development of low toxin varieties of grass pea is a matter of food security and is something that will have a direct impact on the health and livelihood of thousands of people. Grass pea takes on a special importance in the light of climate change since tolerance to drought and flooding are characteristics that give the crop an advantage in stressful conditions.
Who knows, maybe grass pea will be up for sainthood after all!
- Sarah -