Manioc marriage mystery unearthed

Image: Wikimedia Commons.

Image: Wikimedia Commons.

Echoing Forrest Gump’s famous box of chocolates quote (number 40 in the American Film Institute’s Top 100 movie quotes), you never really know what to expect when you get married. Well, certainly in some parts of Africa you may get more than you bargained for!

Investigating marriage practices in small African farming communities in Gabon, Marc Delêtre and colleagues discovered a remarkable connection with the genetic diversity of manioc, which clustered and was lowest in the north and highest in the south of the region. Manioc – probably better known as cassava (Manihot esculenta) in Europe – is native to South America, but is extensively cultivated as an annual crop in tropical and subtropical regions for its edible starchy, tuberous root, a major source of carbohydrates.

In the rather technical language of the abstract, ‘spatially explicit Bayesian clustering methods showed that geographical discontinuities of manioc genetic diversity mirror major ethnolinguistic boundaries, with a southern matrilineal domain characterized by high levels of varietal diversity and a northern patrilineal domain characterized by low varietal diversity’. Alternatively, in the more accesible language of a press release: in the south of the region, a bride brings to her husband’s village manioc varieties from her mother’s farm; in the north, new brides turn up manioc-free and rely on gifts of manioc varieties from their mother-in-law. All of which manioc mayhem of mixing-and-matching provides an important – if maybe unexpected – human dimension to geographical patterns of crop diversity. However, one is left wondering on what basis men in those regions choose their wives: is the manioc – and the future family’s food security – more important, or is a cheerful disposition, etc, more sought after?

Although a staple crop for approx. 250 million sub-Saharans, cassava is notoriously poor in protein – a cassava-based diet provides less than 30% of the minimum daily requirement for protein – and contains compounds that release hydrogen cyanide (which is poisonous!). Welcome news, indeed, then, that Narayanan Narayanan et al. at the Donald Danforth Plant Science Center (St. Louis, USA) have delivered a ‘double-whammy’ to cassava research, which not only reduces cyanogen content, but also increases protein levels. Using a GM approach they created plants that over-express hydroxynitrile lyase (HNL), which accelerates production and hence also loss of HCN during food processing, and – because the HNL is located in the cell walls, which survive the processing – leads to an increase in protein content of the foodstuff! How cool is that! And yes, there’s even more good news on the cassava front. Nearly US$12 million – from the Bill & Melinda Gates Foundation, The Monsanto Fund and the Howard Buffett Foundation – has been provided to VIRCA (the Virus Resistant Cassava for Africa project). The hope is to generate cassava resistant to such viruses as CBSD (cassava brown streak disease) and CMD (cassava mosaic disease), which are causing major, devastating losses to cassava crops in Uganda and Kenya; indeed, CBSD is listed as one of the seven most dangerous plant diseases in the world for the impact it can have on food and economic security across Africa. And news that will be boosted by the announcement that BGI (formerly the Beijing Genomics Institute) will ‘work with Colombia’s International Center for Tropical Agriculture (CIAT) to sequence 5,000 cassava genotypes in a project that will aid scientists as they improve the crop through genetic engineering’. Which itself is on the back of the first draft of the cassava genome published in late 2009. Yes, 2011 has been a good year for manioc/cassava/yuca/mogo aspirations – let’s hope 2012 is even better because 500 million people worldwide are relying upon it!

About Nigel Chaffey

Nigel is a botanist and full-time academic in a UK university. As News Editor for the Annals of Botany he contributes the monthly Plant Cuttings column to that august international botanical organ. His main goal is to inform (hopefully, in an amusing, educational, and entertaining way...) about plants and plant-people interactions.