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!

Nigel Chaffey. ORCID 0000-0002-4231-9082

Nigel is a botanist and full-time academic at Bath Spa University (Bath, near Bristol, UK). 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 educational, and entertaining way...) about plants and plant-people interactions.