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  • Combining cassava species could lead to better crops

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[SAO PAULO] Combining tissues from different cassava species may lead to a new method for improving this staple crop for some 800 million people around the world, according to Brazilian researchers.

In a paper submitted to HortScience, they show that hybridising a wild species with a cultivated one could result in a crop that combines the best traits from both parent species and increase productivity by up to five-fold.

They combined tissues from Manihot fortalezensis — a wild, drought-resistant cassava species well adapted to borer pests in its native Brazil — with a cultivated variety, M. esculenta UnB 201, which is nutritious but low-yielding, and is susceptible to drought and borer pests.

The resulting hybrid, known as a chimera, had 7–8 edible roots that weighed 10–12 kilogrammes, compared with M. esculenta UnB 201 — which produced just 4-5 edible roots that weighed 2–3 kilogrammes in total — and M. fortalezensis, which produced no edible roots.

Chimeras have deep fibrous roots like their wild parent, which the researchers say indicates they can capture water deeper down indicating drought tolerance. The plants also showed "extremely vigorous growth compared to their parents", growing much bigger than their parent species.

But, so far, the researchers have produced only 18 plants and studied them at one year of age, and the chimeras smelled of an acid known as hydrogen cyanide (HCN), which can be toxic when the cassava is not properly processed.

Nagib Nassar, lead author of the study and researcher at the University of Brasilia, Brazil, said that the new variety uses a simple botanical tool of grafting (combining tissues from two plants) and therefore does not pose risks to human health or to the environment, as may be the case with genetically modified (GM) varieties.

"[As they belong] to the same genus (Manihot), both species' tissues can grow and live together in a [single] organism," he told SciDev.Net. This means the tissues arising from the parent species can "harmoniously coexist" in the same plant without using GM tools, he added.

Maria Teresa Bertoldo Pacheco, a researcher at the Sao Paulo Food Technology Institute, Brazil, said that the study's results may lead to more robust and tolerant cassava cultivars.

But she told SciDev.Net: "To [ensure] this variety cultivar is edible, additional studies focused on the chemical, nutritional and toxicological composition are essential".

Mário Takahashi, researcher at Paraná Agronomic Institute, Brazil, questioned the cost effectiveness of the study's technique and whether they would ever reach the farmers.

"Lots of work had already been done with the cassava plant's culture, but almost none of it [reaches] farmers," he told SciDev.Net.

However, Nassar said that this cassava variety could easily be cultivated on a large scale and distributed to farmers, and that the main purpose of this initial study was to make the technique known in the scientific community in order to be reproduced and explored.

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