Category: Nutrition

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Cassava, revisited, and revisited again

Cassava has been a persistent thread through this blog since the beginning. It first appears as a staple with a dark side: capable of keeping people fed, but also of causing a nasty disease under some conditions. Over time, it resurfaced repeatedly, showing how one crop can illuminate many of the key issues in agrobiodiversity conservation and use. As part of our anniversary celebrations, let’s pull some posts out and see how that might work…

An early post we called Detoxifying cassava looked at the complex ways konzo epidemics in Africa are linked to the consumption of bitter cassava. A later Nibble pointed to a very digestible (sic) introduction to cassava and cyanide. And Manihot esculenta, I presume? widened the lens historically, drawing on Dr Livingstone’s Zambesi Expedition papers to show how he understood cassava’s diversity, its promise and its danger back in the day.

Several posts over the years have looked at how well we now know and conserve the diversity of the crop. Gaps in cassava collection in Africa highlighted sounded an alarm: eastern and southern Africa seemed to be under‑represented in international genebanks. Later, More on cassava germplasm from Brazil and an earlier post compared the geographic distribution of CIAT’s genebank holdings with the that of both accessions and cultivation in Brazil, illustrating how national and international collections overlap — and where they don’t.

A post on safety duplicating germplasm collections explained the mechanics of backing up diversity, using Embrapa’s genebank as a concrete example. It also included a reference to the global cassava conservation strategy, during the development of which I got schooled on the diversity of the crop. And a paper on sources of pest resistance in cassava we included in a Brainfood showed the value of genebank holdings, identifying landraces in CIAT’s global collection with resistance to thrips, mites, and whiteflies.

This particular arc culminates in a summary of two papers on 50 years of cassava conservation at CIAT, which looks at that genebank from both ends: what went in over five decades, and what actually came out in breeding. A recent Nibble notes that cassava’s diversity is spread across multiple genebanks, and why that’s a good thing, up to a point.

Then came the TME 419 saga: Is there more than one TME 419 cassava? unpacked confusion around an IITA genebank accession number; I say TME 419, you say TMe‑419 revisited the same named clone in Nigerian fields years later. Another intricate tale centred around how some modern varieties got their resistance to post-harvest rotting. Spoiler alert: a wild relative was involved.

Genebanks, however, are not the full story. Cassava’s diversity also has to survive in farmers’ fields, where diseases constantly test its resilience. An early post, Ho hum … another deadly disease, placed cassava brown streak virus (CBSV) alongside then emerging threats like Ug99 wheat rust. CBSV was duly much in the news a few years later in 2011, and we were of course all over it, though not always one hundred percent correct in our judgements. That’s what the comments are for.

A Nibble on cassava pests questioned the crop’s “indestructible,” Rambo-like image as new problems appeared in Southeast Asia and elsewhere. An experiment on cassava degeneration, Twitter‑style focused on what to do about the widespread viral infection of cassava planting material across Africa, which badly affects performance. And a Nibbles roundup on cassava bad and good news captured an apparent mismatch between FAO worry and CGIAR optimism back in 2011. Maybe we should do an update on that, now I think about it.

Another theme has been how the crop is promoted, produced, and woven into everyday food systems today. In Cassava on a roll? I traced production ups and downs in Kenya, intrigued by seeing new products in supermarkets on my return to the country. I followed that up with The flour of Kenyan agrobiodiversity marketing, which shows cassava (with finger millet) being used to diversify staple flour, connecting conservation to real products and diets. And a Nibble on Ugandan cassava from a couple of years back highlights local innovation in value chains, if you interpret it charitably. No doubt all part of the African cassava revolution touted by Forbes in a 2023 Nibble.

I hope this roundup of our past encounters with cassava, incomplete as it inevitably is, has given you a little taste of what twenty years of this blog have been about: following stories as they unfold, picking up old threads, occasionally digging really deep, other times not deep enough. Do search for your favourite crop in the archive, and tell us what you come up with.

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Nibbles: African food systems, Uganda cassava, Uganda pastoralists, Butternut conservation, Seed transfer zones webinar, Frozen Zoo, India fish genebank

  1. Swapping maize for indigenous crops won’t fix African food systems designed around markets and policies that still favour a narrow range of crops.
  2. Cassava is both a food security fallback and a commercial crop in Uganda, but disease, climate change and declining diversity make its conservation an increasingly urgent form of insurance. But what about the markets and policies?
  3. When livestock and crops fail, Ugandan pastoralists draw on wild plants for food, underlining how much food-system resilience still sits outside the formal agricultural system, with its markets and policies.
  4. The Morton Arboretum is using living collections and genetic research to help the threatened butternut tree cope with changing conditions.
  5. Webinar discusses global approaches to seed provenancing and transfer zones, useful for anyone who wants to move native plants without moving the wrong genes. Butternut very interested.
  6. San Diego Zoo Wildlife Alliance’s Frozen Zoo preserves genetic material of plant and animal species that may disappear, from DNA to cells to organisms. Butternut volunteers.
  7. New Indian facility combines ex situ fish conservation with community aquaculture. Good model for much of the above?
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Brainfood: Nutrition edition

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Joining the dots on food plant diversity

We have access to more kinds of food plants, yet the world’s diets and production systems have never been more alike. That is the paradox at the heart of Food plant diversity in a rapidly changing world, an unusually broad review by Colin Khoury (very much friend of the blog) and colleagues. It has all the latest data, but it also does several other things that make it more than a conventional state-of-the-art paper.

For one, it brings together diversity at several levels that are too often discussed separately: species, varieties and genes, of course, but also the diversity of diets, farming systems, foodways and the knowledge associated with them. It traces the movement of cultivated food plants over the past 12,000 years alongside the much more recent trend towards homogenisation. The result is the weird world we live in today: more kinds of crops available globally, but less difference between what people in different places eat.

Colin and friends also take a hard look at what we don’t know. We have surprisingly little evidence for how much food-plant diversity has actually been lost, how vulnerable today’s production systems are because of increasing uniformity, or what is happening to less visible forms of diversity, such as nutritional and chemical variation. The authors call for better monitoring, including an early-warning system for crop vulnerability. Now where have I heard that before?

And the paper connects the dots between conservation approaches that all too often live in isolation: genebanks, botanic gardens, community seed banks, on-farm initiatives, protected areas, breeding programmes and markets. Genebanks are all well and good, but diversity also needs to keep going in fields, landscapes, cuisines and communities. Again, not particularly new, but it’s good to have it repeated, brought up to date, and placed in the broadest possible context.

A couple of those dots are discussed in more detail in a companion opinion paper, Enhance food plant diversity conservation and use through greater coordination between genebanks and botanic gardens, which asks what might become possible if two of the world’s major plant conservation communities worked a bit more closely together. Which must be possible because they are nicely complementary, so neither should fear the other as a competitor.

The review paper maps the problem. The opinion piece explores a possible route towards a more joined-up conservation system. Which leaves us with its own small paradox: conserving food plant diversity requires flattening some of the differences within a remarkably diverse conservation community. Happy Crop Diversity Day 2026.

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Where have all the nutrients gone?

The “nutrient collapse” story has been doing the rounds for years, and we’ve been picking at it on the blog for almost as long.

Back in 2009, Jeremy looked at evidence that older crop varieties could contain more minerals, protein and other nutrients than newer ones, and discussed various possible reasons, including the intriguing possibility of a “genetic dilution” effect as breeders selected for yield.

By 2012, we were stressing that the evidence was more complicated than the headlines suggested, and in 2019 we linked to the latest critical review of the evidence by Robin Marles of the Bureau of Nutritional Sciences in Canada.

Now the latest episode of the BBC’s indispensable More or Less podcast asks again whether carrots are becoming less nutritious, prompted by a listener who clearly hasn’t been following our blog, and turns to Dr Marles, now retired, for the answer. Which hasn’t really changed much.

The bottom line is that breeding for yield and other commercially important traits can change the balance of what ends up in the harvest, and that we have historically been much better at measuring tonnes per hectare than what is actually in those tonnes.