Feeding the future: mapping a path to improved cassava production

Associate Professor Ros Gleadow

Associate Professor Ros Gleadow

A billion people around the world eat the cassava plant every day. Easy to cultivate and drought- tolerant the fact that it is eaten by so many means that attacks by pests and diseases have huge impact on food security. It’s also the only staple crop that can kill you or cause chronic neurological disease if it’s not processed, potentially producing fatal levels of cyanide when drought-stressed.

To help improve strategies for breeding disease resistant and climate tolerant varies of this root crop, an international research team led by the University of California, Berkeley, the US Department of Energy Joint Genome Institute (JGI) and including scientists from Monash University, have for the first time, mapped cassava’s genetic diversity.

Monash biologist Associate Professor Ros Gleadow explained the significance of this latest research, published today in Nature Biotechnology.

“Until now, very little research has been done at the DNA level – the genome – of cassava, the world’s fifth most important crop,” Associate Professor Gleadow said.

“To maintain food security, it’s critical that cassava is resistant to disease and resilient to climate change. Our new research has revealed the genetic relationships between different cassava varieties from across the world and compared them with other species in the same group, such as rubber trees. We have also captured the global genetic diversity of 53 varieties of cultivated cassava and its wild relatives – from South America, where it was first grown 6,000 years ago, to Africa, Asia and Oceania,” Associate Professor Gleadow said.

The Monash research team co-ordinated the sequencing of cassava varieties from Oceania; Fiji, Vanuatu and Australia. The findings indicated genetic differences between the varieties and will therefore help inform the production of more resistant and safe cassava crops using these and other favourable varieties from across the world.

For the Monash team, the new research also provides a way to better understand why cassava produces toxins under conditions such as drought and how that can be safely reduced in the growing plant without jeopardising pest resistance.

“The sequencing of these different genotypes allows us to look at how cyanide and other traits are inherited and why some varieties produce more cyanide than others - enabling us to develop new strategies to produce less toxic varieties that are still disease resistant,” Associate Professor Gleadow said.

The research team found that the genetic diversity of cassava used in current breeding efforts has been greatly reduced in Africa, where viruses such as the cassava mosaic disease and the cassava brown streak disease have affected crop yields in many nations. This poses a real threat that a new disease could wipe out an entire crop.

The team were able to detect the genetic signature of past cassava improvement programs going back to the 1930s, which interbred cassava and Ceara rubber, and the persistence of these Ceara rubber regions in the best cassava varieties suggests they offer positive attributes. The team also discovered relationships between many cultivated cassava varieties, which could help breeders maximise genetic diversity in improvement programs.