Bioversity International

Roughly half of the world's population suffers from some degree of vitamin A, iron and zinc deficiency, and one of the great challenges to current nutrition and health policies is to deliver a sustainable increase in dietary intakes of these micronutrients in afflicted areas. Bioversity has long worked to improve nutrition by promoting an increased overall diversity of diet. At the same time the organization has not neglected biofortification, which is the idea of increasing the nutrient contents in staple crops. Bananas and plantains (Musa spp.) are just such a staple food for millions of people, especially in the developing world. In some parts of the world, for example the Pacific, a single orange-fleshed banana can provide the entire adult daily requirement of vitamin A precursors. Might a similar approach be available in Africa?

Bioversity, as part of the CGIAR's HarvestPlus Challenge Program, undertook the task of assessing and logging nutritional variability in bananas and plantains. The broad aims were to help breeders and nutrition experts to make the most of existing Musa varieties by analyzing which have the highest micronutrient levels and how best they might be grown, harvested, stored, prepared, processed and consumed to retain micronutrients. At the most practical level, the project has set out to ensure that these varieties become easily available to the undernourished people who need them most.

Mark Davey, a project team member based at Katholieke Universiteit Leuven, in Belgium, recently reported encouraging progress in screening bananas and plantains for vitamin A precursors and other micronutrients. To date more than 170 different varieties have been screened for the provitamin A carotenoids (pVACs) contents in their fruit, and a subset of 47 of those have been screened for iron and zinc.

The results show that there is a lot of variation in mean concentration of fruit pulp pVACs among the different banana and plantain varieties and that varieties with high fruit pVACs are widely distributed across the different genome groups, but only at a low frequency. It takes no great leap of faith to see that the introduction of such varieties into the diet at modest and realistic levels of consumption has the potential to improve the vitamin A status of people who depend on bananas and plantains.

"We did a study to see what the impact of using high-pVACs varieties would be on vitamin A deficiency using household data from plantain-growing regions of Ghana," explained Inge van den Bergh, Bioversity's project coordinator. "We predict it would reduce the burden of illness by almost a fifth, and it would be more cost-effective than other kinds of intervention."

By contrast, concentrations of iron and zinc were low and showed limited variability among the varieties, even where the different types were grown under widely-differing environments and soil types.

"This knowledge provides us with the necessary data and new hope for developing a successful banana and plantain breeding programme for new varieties with enhanced nutritional content and for the direct introduction to farmers of varieties that are naturally rich in carotenoids," said Davey.

The study demonstrates that within the Musa germplasm pool there is abundant genetic diversity in the levels of vitamin A precursors in the fruit. In the past it had been assumed that there just was not enough variation to make Musa worth exploring for better nutrition though biofortification. In fact the existing diversity can be exploited both to identify varieties potentially suitable for direct introduction in afflicted regions and to use in breeding programmes to increase the vitamin A content of this very important staple food.

Another important consideration in favour of this approach is that farmers traditionally grow a wide range of banana and plantain varieties. It would thus be relatively easy to integrate varieties high in vitamin A precursors into the production systems, and they would probably prove acceptable to consumers too.

On the negative side, the high sterility of most banana and plantain varieties means that breeding for such traits is likely to be a lengthy process. And the challenges do not stop there. Before the widespread introduction of new and possibly unfamiliar types of banana and plantain can take place, detailed agronomic trials will have to be carried out to optimize production conditions.

Another potential problem is that previous results from plantain breeding have indicated an inverse relationship between the intensity of the orange colour of fruits (which is linked to the amount of pVACs) and suckering growth. In other words, pale-fleshed varieties produced good suckers that fruited relatively quickly, a good thing for farmers, while more orange-fleshed varieties produced small suckers and took longer to fruit. It remains to be seen whether these two traits—growth cycle and pVACs—can be uncoupled from each other, or whether breeding for fruits with high pVACs automatically has an adverse effect on the performance of the variety.

Worldwide there are well over a thousand banana and plantain varieties, which suggests that as more germplasm is screened it should be possible to identify novel sources of types rich in vitamin A precursors. However, in contrast to other crops, the degree of genotypic variation in iron and zinc is limited in Musa. Thus, while bananas may become a much richer source of vitamin A, people and researchers will have to look elsewhere for iron and zinc. Fortunately, there are many other local crops that can meet those needs.

Further information

i.vandenbergh(at)cgiar.org

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Bananas and plantains vary widely in their provitamin A carotenoids (pVACs) contents. pVACs-rich cultivars could help overcome vitamin A deficiency in diets of people who depend on bananas and plantains.