Long-life cassava won’t work – but longer-life could be the answer

19 February, 2013 by (comments)

CIAT Cassava breeder Hernan Ceballos has called time on hopes of developing long-life cassava roots.

“In terms of roots that can last for months after harvest, the dream is over,” he told delegates at a workshop of the CGIAR’s Roots, Tubers and Bananas (RTB) research program, at CIAT’s headquarters in Cali, Colombia, today. “Cassava will not turn into a potato,” he said, a reference to the latter’s excellent storage quality.

But encouragingly, his current research suggests that developing cassava roots that can last just a week without spoiling – longer-life rather than long-life – could enable farmers to overcome one of the most significant bottlenecks in the cassava processing chain.

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Cassava roots perish very quickly after harvest and are normally completely spoiled after three days. This process, known as post-harvest physiological deterioration (PPD), is a major constraint for cassava producers – both big and small – who have to rush the roots to markets or starch processors. It’s a challenge complicated by poor rural infrastructure in many cassava producing areas, and a major obstacle to cassava fulfilling its potential as one of the most climate change-resilient crops for sub-Saharan Africa.

In early 2009, CIAT scientists made the chance discovery that a cassava variety conserved in the organisation’s gene bank that contained naturally high levels of beta-carotene, was able to resist PPD for up to two months. If the scientists could establish a causal link between the antioxidant properties of beta-carotene and PPD tolerance, new cassava varieties with much longer shelf-lives could be developed, and cassava roots could become as easy-to-store as potatoes.

But subsequent CIAT research found that despite the roots lasting longer, their starch content fell gradually over time – and it’s the starch that makes cassava such a valuable food and industrial crop.

“After you harvest it, the root is still breathing; the starch turns into carbon dioxide and water, and some starch is turned it into its basic component, sugar,” Hernan told me during the break. “The roots are not spoiled, but the quantity of starch is falling. After a couple of weeks you have, maybe, 10 per cent less starch than at harvest. In a month, we estimate that the starch content is 30-40 per cent less. Losing that amount of starch is not acceptable.

“So now we’re focusing on roots that can survive the first week-to-ten days after harvest – that’s where 90 per cent of the losses occur in the cassava processing chain. It means that if a truck breaks down and a farmer can’t get the roots to the processing factory, they won’t lose everything. The starch content of the roots will end up slightly lower, but they will still be valuable and the farmer will have a few days to get the truck fixed.

“It’s buying time at the most sensitive time in the processing chain.”

A doubling of the cassava shelf-life is certainly not to be sniffed at, and can also mean a lot to cassava processors. During the discussion, Bussie Maziya-Dixon, cassava breeder at the International Institute of Tropical Agriculture (IITA), said that the quality of gari – a popular West African food made from mashed and fermented cassava roots – decreases drastically when the root processing is delayed by one-to- two days after harvest. Longer-life cassava could make a big difference.

While Hernan himself also believes it’s possible that one day there will be a market for sweeter cassava products, made using long-life roots whose starch has turned to sugar, he reiterated that “the dream of roots that store for months and months is out of the picture now.”

The Strategies for improving livelihoods through RTB post-harvest technologies workshop runs all week at CIAT’s headquarters in Colombia.



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