Accelerating the Rate of Genetic Improvement in Cassava

Genetic improvement of cassava has been slow because the biology of cassava makes the traditional breeding cycle very long, seriously limiting the responsiveness of cassava breeding to emerging threats, and preventing rapid delivery of improved varieties. The Next Generation Cassava Breeding project aims to meet these challenges and revolutionize cassava breeding through the application of an advanced breeding approach called genomic selection (GS). GS evaluates seedlings based on genotype alone, bypassing the need for expensive and time-consuming yield trials, with the goal of dramatically increasing the rate of genetic improvement of cassava. Our pilot study used historical clones from IITA’s breeding program as a “training population”: prediction models for several traits were developed from next-generation DNA sequence data and historical phenotype data.  Our preliminary results indicate that prediction accuracies for cassava are similar to those for other species given the training population size. Thus, the atypical aspects of cassava (i.e., clonal propagation and high levels of heterozygosity) are not negatively affecting prediction accuracies in ways we do not understand. Given that we anticipate that genomic selection can accelerate the breeding cycle of cassava between two and a half and five fold, our results indicate that rates of improvement under genomic selection will be more rapid than under phenotypic selection. The Next Generation Cassava project will implement GS in three African breeding programs, and develop the tools and methodology, as well as human and infrastructure capacity, to ensure the long-term application of GS in cassava breeding in Africa and beyond.