50 years of cassava diversity: what went into the bank, and what came out

Two new papers in Plants, published two months apart, tell the story of CIAT’s cassava genebank from opposite ends: how the collection was assembled and conserved, and what breeders have actually done with it. Read together, they amount to a remarkably candid 50-year audit of a slow-motion agricultural asset.

Part I is the origin story. Botanist Victor Manuel Patiño’s 1969–70 expeditions alone brought in roughly a third of today’s 5,000 or so cassava landraces, transported as stem cuttings across Colombia, Ecuador, Venezuela and beyond, often in difficult conditions and under changing quarantine rules.

The collection has its blind spots: Brazil and the Guianas remain poorly represented, passport information is patchy, and the overwhelmingly male composition of collecting teams probably meant that some of the varietal knowledge held by women farmers went unrecorded.

Conservation itself has been a moving target. It has evolved from field genebanks to in vitro slow-growth storage after a frogskin-disease scare forced the field collection to close in 2003, and now towards cryopreservation at CIAT’s Future Seeds facility. Meanwhile, DNA fingerprinting keeps revealing an awkward truth familiar to genebank curators everywhere: the names people give varieties and their genetic identities do not always agree. A lot of effort has gone into testing for pathogens to ensure that distribution is safe.

Part II asks what all this diversity is actually for? The answer has also changed considerably over five decades. Early researchers chased traits such as high protein content and low cyanogenic content before turning towards yield and starch percentage in the Green Revolution era.

The payoffs have been tangible: landraces have contributed traits such as resistance to pests and diseases, adaptation to acid soils and highland cold, and quality traits for fresh-market cooking versus industrial starch. The route from accession to released variety is rarely direct: a landrace gets screened for a trait, crossed, then recombined and selected over several more generations before anything reaches a farmer’s field. The results include varieties like Nataima-3, bred for whitefly resistance thanks to an Ecuadorian landrace. At the same time, the authors argue that cassava breeding now needs to move beyond broad phenotypic selection towards more systematic use of inbred lines, because the crop’s high heterozygosity makes the introduction of specific traits particularly difficult.

The two papers therefore tell a big story about genebanks. Collecting diversity is only the beginning; its value is realized decades later, when a breeder encounters a problem that nobody could have anticipated when the stuff was first collected. The cassava collection is a long-term portfolio of biological options, one whose contents have taken half a century to assemble, whose inventory is still being corrected, and whose most valuable assets may be the ones that have not yet been used.

A new project is looking to engineer cassava to photosynthesize more efficiently at higher temperatures. I do wonder whether someone has already checked whether any of those 5,000 landraces might help with that. Maybe they can’t, but it’s worth having a look. And you never know, something else of interest might jump out. That’s the beauty of large international collections of crop diversity such as CIAT’s.