Native plants could benefit African farmers

1 March 2010 by Tom Marshall

Indigenous African legumes could provide an alternative to less suitable plant species introduced from abroad, to help combat hunger, poverty and ecological devastation on the continent.

African market

Modern biological expertise means native plants could quickly be bred or genetically modified to capitalise on their strengths. Research suggests these plants are better suited to African conditions than many imports.

The legume family includes all peas and beans; its members range from peanuts to acacia trees. Nearly all are distinguished by their ability to house bacteria in swellings, or nodules, on their roots that draw nitrogen out of the atmosphere and 'fix' it into proteins and other vital compounds.

This means legumes don't just need less artificial nitrogen fertiliser to grow; in some cases they can even improve the soil, creating a surplus of nitrogen that helps other plants. With populations continuing to grow, and climate change and desertification predicted to reduce the available area of land that can be farmed, the ability to grow more food while adding less fertiliser will be crucial over the next century.

Over-reliance on a few species is risky - outbreaks of disease or insect pests could trigger widespread famine. "We urgently need more diversity of crops," says Janet Sprent, Emeritus Professor of Plant Biology at the University of Dundee and lead author along with two senior African colleagues of a recent paper on the subject in the Journal of Experimental Botany. "If most of Africa is dependent on soybeans, all you need is one pandemic and there could be more starvation in the continent. We need a range of different crops suited to different environments."

During the twentieth century, foreign legume species were introduced to Africa. These include soybeans and peanuts, also known as groundnuts - the latter were brought in under a British-backed project in the middle of the century.

Despite their heavy yields and worldwide popularity, such imports aren't necessarily best suited for African conditions, and Sprent believes native species could be bred to create better crops before too long.

"This needs to be done on a local level - we should be finding out which crops are suitable for specific areas," Sprent says. "The world is getting drier, and in some areas farmers need plants that can handle dry conditions and high salinity. We have to find better options to help African farmers cultivate marginal land."

The study gives several examples of native plants that could provide alternatives to widely-grown foreign species, particularly if more effort were made to support crop improvement programmes using selective breeding and genetic analysis. As well as improving food security, these crops could bring other benefits such as increasing the amount of carbon held in soils, and adding to the diversity of microbes living there.

For example, the cowpea (Vigna unguiculata) is widely grown in Africa as a multipurpose crop, providing grain, edible leaves and forage for animals. It doesn't need as much fertiliser as rivals, and some types have a large, vigorous root system that provides good resistance to dry conditions.

It can also fertilise the soil with nitrogen, benefiting crops it is grown alongside, although at present there is great variation in nitrogen fixation - an area in which Sprent and colleagues think efforts at crop improvement could have major benefits. Other members of the same genus can grow in salt-contaminated land - a major problem in Africa due to misguided irrigation programmes in the past.

African acacia trees are another example. These could offer a better alternative to imported acacias and eucalypts, which tend to need far more water than native trees. These plants are already grown to produce products like gum arabic, a vital cash crop for many African farmers. If scientists could create acacias that fixed more nitrogen in the soil and produced more and better gum, these farmers' lives could be greatly improved.

Crops like these could allow what is now marginal land to be cultivated productively. For instance, prairie-like rangeland habitats are too dry for intensive crop cultivation, but are well suited to a mix of grazing animals, forage crops and small-scale growing of crops for human consumption.

Sprent believes that working with local farmers and providing them with the tools of modern plant science is crucial. "We still have a tendency to tell local farmers they must do this or that, but they have a lot of knowledge and ingenuity - whenever I go to Africa I learn a lot more than I teach" she says. "If we work with local people we can put that knowledge to work."

Plants could be modified with a range of techniques. These range from selective breeding with the aid of modern genetic analysis to speed up the process by identifying which genes are of most interest, to full genetic modification, which would allow greater flexibility in changing a plant's genetic makeup.

'African legumes: a vital but under-utilized resource' - Janet I Sprent, David W Odee and Felix D Dakora, November 2009, Journal of Experimental Botany, doi:10.1093/jxb/erp342