Fast-tracking nutrition: A magical discovery

8 October, 2013 by (comments)

Newly bred crop varieties that offer quadrupled vitamin A content could provide a lifesaving solution to millions in Africa suffering from malnutrition related to vitamin A deficiency.

Globally, an estimated 250 million children are vitamin A deficient, according to the World Health Organization. Up to 500,000 will go blind every year – half of them will die within 12 months of losing their sight.

A severe lack of the vitamin also puts vulnerable children and pregnant women, particularly in the developing world, at risk of disease and even death from common infections like measles.

“The tragedy of so many children going blind due to lack of vitamin A in Africa has prompted us to address food quality as well as quantity,” said CIAT plant breeder Hernan Ceballos.

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This has led Ceballos and his research team to fast-track improvement in the nutritional value of cassava, Africa’s second most important staple crop. Radical results indicate a fourfold boost in beta-carotene – the orange pigment used by the body to make vitamin A – from 5 micrograms to about 20.

The work is all the more remarkable because it has been done in record time. Usually, the selection process needed to demonstrate genetic gain takes about 8 years – the time required for just one normal cassava breeding cycle.

But researchers didn’t have time. To meet the ambitious 10-year goal set by the Bill & Melinda Gates Foundation, which funded the research, they devised a “rapid-cycling” breeding method to turn the impossible into reality.

“It was magical,” said Ceballos. “None of us suspected that it would be possible to achieve such a large increase so quickly.”

Stretching the boundaries of science

Unlike other genetic traits of cassava, beta-carotene is “trustworthy”. That is, you can demonstrate increased or decreased levels in a short time, without carrying out multi-location trials and multiple root tests to verify results.

This is typical of what scientists call “high-heritability” genetic traits. In humans, blue or brown eyes are an example of such traits – a “reliable” result can be determined relatively soon after birth. An IQ, by contrast, is a low-heritability trait – one that takes years to become evident.

“Root yield is an example of a low-heritability, elusive trait because it is very site specific,” explained Ceballos. “One genotype could give certain results in one location but 10 kilometers away things could be completely different. The results are unreliable.

“You need to test in multiple locations, which will take about 8 years,” he continued. “We suspected that beta-carotene had high heritability at the beginning, but now we know it for sure.”

Because beta-carotene is a high-heritability trait, only one plant per cassava variety was tested and crossed with other roots of high beta-carotene content. This “rapid-cycling” process reduced the cassava breeding time from 8 to 3 years.

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“There are very few reports on how much cassava responds to breeding gains from selection,” said Ceballos. “This is a breakthrough because for the first time, we have demonstrated that such fast progress can be made in manipulating a single trait.”

“This research also demonstrates that cassava is actually very responsive – we can chisel out a focused response provided that the trait has high heritability” he added. “It’s hugely exciting.”

Unravelling the mystery

The results have implications beyond boosting beta-carotene content in cassava. By unravelling a bit more of the mystery surrounding the genetic makeup of the crop, scientists now know that rapid breeding for other high-heritability traits is possible.

Resistance to high-heritability diseases, for example, could be tested more rapidly. “For the first time, we can use this knowledge to inform our decisions when developing new varieties,” said Ceballos.

But there are a number of hurdles that still need to be overcome in fully applying this research. “The work on beta-carotene is tremendous, but it’s not a silver bullet,” admits Ceballos.

There still remains the hard work of getting the improved varieties, or source material, into the field where farmers can use them – and ensuring that they are accepted by farmers. This baton has been picked up by CIAT’s partner, the International Institute of Tropical Agriculture (IITA).

“What we have done is to demonstrate that cassava responds very well to the rapid breeding process, and we have developed source materials with high beta-carotene for further breeding,” said Ceballos.

“We have made fantastic progress in boosting the nutritional content of cassava, and now we’ll concentrate on production of commercial varieties, for use in Africa and Latin America.”

Able to withstand disease, drought, and pests, cassava is eaten where poverty and malnutrition are widespread. Boosted vitamin A will benefit about 70 million people in developing countries who consume 500 calories from cassava roots every day.

This work was funded by the Bill & Melinda Gates Foundation and contributes to HarvestPlus, a global leader in developing biofortified crops with more than 200 agricultural and nutrition scientists around the world. Coordinated by CIAT and the International Food Policy Research Institute (IFPRI), HarvestPlus forms part of the CGIAR Research Program on Agriculture for Nutrition and Health.

Read the article published in Crop Science: Rapid Cycling Recurrent Selection for Increased Carotenoids Content in Cassava Roots

For more information contact Georgina Smith: g.smith@cgiar.org

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