Mystery of sweetpotato origin uncovered, as missing link plant found by Oxford research

Years of careful taxonomic research by a team led by Robert Scotland, Professor of Systematic Botany at Oxford Plant Sciences, and funded by the UK's Biotechnology and Biological Sciences Research Council, has concluded with the discovery of a new species that is sweet potato’s closest wild relative, Ipomoea aequatoriensis.

How the sweet potato evolved has always been a mystery. Now, we have found this new species in Ecuador...a fundamental piece of the puzzle to understand the origin and evolution of this top-ten global food crop

Professor Robert Scotland

This species, which most likely played a key role in the origin of the crop, is the latest in a series of discoveries by the Oxford team and collaborators at USDA and the International Potato Centre Peru, and one that represents an ‘extraordinary discovery in untangling the evolution’ of the plant, according to the researchers. 

Professor Scotland says, ‘How the sweet potato evolved has always been a mystery. Now, we have found this new species in Ecuador that is the closest wild relative of sweet potato known to date and is a fundamental piece of the puzzle to understand the origin and evolution of this top-ten global food crop.’

The group's work on the sweet potato and its wild relatives - the morning glory family - led two years ago to the publication of a massive monograph, detailing the plant’s dispersal, variations and history.

Our finding is the result of several years of team work...the integration of different techniques and a good taxonomic knowledge made it possible

Dr Pablo Muñoz-Rodríguez

This painstaking work has already rocked some accepted theories. The Oxford team showed the sweetpotato could have arrived in the Pacific islands by natural means and before people, challenging popular ideas about the arrival of humans in some locations. According to the team, today's research show how much progress can be achieved when biodiversity studies are supported by good taxonomy.

Such work is key to understanding the plant world and being able to conserve it, insists Dr Pablo Muñoz-Rodríguez, postdoctoral researcher and joint first author of today's paper, ‘Our finding is the result of several years of team work. It required a deep understanding of the sweet potato and its close wild relatives, their morphology and their evolutionary relationships. It was the integration of different techniques and a good taxonomic knowledge that made it possible.’

According to today’s research, previous attempts to identify the sweetpotato’s ‘ancestors’ have been ‘hampered by taxonomic confusion’. 

The search for the ancestor of sweetpotato has been going on for almost a century...but we have been able to definitively identify it. This will enable a better understanding of sweet potato’s origin and contemporary diversity

Tom Wells

Using the latest techniques, the researchers found the missing part of the puzzle between the sweetpotato, which is a hexaploid (having three copies of its genome) and its closest relative, which is a diploid (having one copy). Biologists believed there had to be a tetraploid, which has two copies of the genome, but until Ipomoea aequatoriensis - which is tetraploid -was identified, none had been found.

Graduate researcher Tom Wells and joint first author maintains, ‘The search for the tetraploid ancestor of sweetpotato has been going on for almost a century, but it is only today with the combination of rigorous taxonomic study and the latest DNA analysis techniques that we have been able to definitively identify it. This will enable a better understanding of sweet potato’s origin and contemporary diversity.’