Cassava “accident” brings tolerance hope

1 September, 2009 by (comments)

When a consignment of carotene-rich cassava roots was packaged and sent for bioavailability tests, there was the usual, hopeful wait for results. Ten months later and those results, soon to be officially announced, suggest that the carotene contained in yellow-flesh of the so-called “egg yolk” cassava has good bioavailability, meaning it can be easily absorbed by humans, and converted into the essential micronutrient vitamin A. This in itself is great news for CIAT and researchers working as part of the CGIAR-wide HarvestPlus program. But the story doesn’t end there.

Cassava root1

In an interesting twist, a handful of surplus roots that were omitted from the consignment and left in a store room were discovered by a researcher two months later – in pristine condition. Cassava roots normally degrade naturally within just two-to-three days, due to post-harvest physiological deterioration (PPD), which leaves them unusable either as food or by industry. Realizing the potential importance of the discovery, the researcher quickly raised the alarm.

“The roots should have been totally spoiled and rotten,” explains Hernán Ceballos, coordinator of CIAT’s cassava program, “but when they were cut open they were completely PPD-free. What was interesting was that the yellow colour of the root had faded away. A biochemical hypothesis can explain this finding: the antioxidant activity of carotenoids gives the root some kind of PPD tolerance.”

The potential impact of the discovery is far-reaching, as PPD is a major constraint on cassava production, transport and processing. “PPD imposes a pressure on the whole cassava production system,” continues Ceballos. “The root has to be taken from the ground and be processed or consumed within three days. Imagine the advantages if farmers could harvest their cassava all at once, store it safely, and plant a new crop straight away. For industry, PPD tolerance means that if a truck breaks down or there is a power cut in a processing plant and it takes a couple of days for things to return to normal, the crop could still be usable.

“This could be an important discovery in solving the major problem of cassava root storage.”

Cassava root2

Despite the excitement, Ceballos and his team are proceeding with caution, and have set up a series of experiments to assess the deterioration of carotenoid-rich roots over periods of up to 40 days. They are also keen to establish whether the supposedly PPD-tolerant roots were affected in some way by a growing season that saw unusual levels of rainfall, and the possible influence of the roots’ lower-than-usual dry matter content, which can reduce the rate of PPD. But the team is hopeful that the discovery backs a previous study from 2004 that found a weak, but positive link between carotenoid content and PPD tolerance.

“Serendipity is a part of the life of a scientist, like Fleming’s discovery of Penicillin,” says Ceballos. “We don’t expect that in 20 years cassava will be stored like potato or sweet potato, but it is possible that roots will be able to be left for two-three weeks from harvest to processing without spoiling. That will be a major contribution.

“Beyond anything else, this shows that there is great value in cassava, and that there are hidden treasures in its germplasm that are just waiting patiently for us to discover them.”

For a related story on PPD in cassava see the Agricultural Biodiversity blog.

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Filed Under: Cassava @en, Crop diversity, Crops @en, Latin America and the Caribbean, Regions