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 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.
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 2 months later—in pristine
condition. Cassava roots normally degrade naturally within
just 2-to-3 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 3 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."
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 scientists,
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 2-3 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.
Contact:
- Hernán Ceballos (h.ceballos@cgiar.org),
CIAT.
Phone: +57 (2) 4450000 (ext. 3125/3031), A.A. 6713, Cali,
Colombia.
- Neil Palmer (n.palmer@cgiar.org),
Public Awareness Officer, CIAT.
Phone: +57 (2) 4450000 (ext. 3008).
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