Cassava is genetically decaying, putting staple crop at risk

For breeders of cassava, a staple food for hundreds of millions in the tropics, producing improved varieties has been getting harder over time. A team at Cornell used genomic analysis of cassava varieties and wild relatives to make a diagnosis: Mutations have corroded the genome, producing many dysfunctional versions of genes and putting at risk a crop crucial to the survival of one-tenth of the world's population. 

"The analysis was cleanly able to show that cassava is genetically decaying," said Ed Buckler, a research geneticist at the U.S. Department of Agriculture-Agricultural Research Service and adjunct professor of plant breeding and genetics at the Institute for Genomic Diversity (IGD) in Cornell's Institute of Biotechnology. "It's getting worse through time as it picks up more and more mutations, so when breeders do make crosses they're having to put more and more effort into finding the few offspring that contain at least one functional version of each gene."

Cassava's challenging position – described by Buckler as "pointed in the direction of extinction" – is likely due to a reduction in diversity during domestication as well as the fact that cassava is spread through cuttings rather than seeds. Without sexual reproduction and the concomitant purging of mutations through recombination, approximately 30 new mutations per generation are accumulating.

The data provide a way forward for breeders to bring greater food security to the tropics by shoring up a key crop that feeds an estimated 800 million people – primarily smallholder farmers – in areas with marginal soils and unpredictable rainfall.