Genetic Load in Cassava

Cassava (Manihot esculenta Crantz) is an important staple food crop for millions of people in Africa and South America. Cassava exposes to a constant mutational pressure due to accumulation of mutations in every generation. To characterize the deleterious mutations in the cassava genome, we constructed a cassava haplotype map using deep sequencing from 241 diverse accessions and identified over 30 million segregating variants. Domestication increased the genetic load in cultivated cassava. Due to limited recombination in cassava, deleterious mutations are ineffectively purged from the genome. Recent breeding efforts shielded the most damaging recessive mutations in the heterozygous state, thus, masking the harmful effects of deleterious alleles to maintain the yield. Purging of these deleterious alleles from the genome should be a key target for future cassava breeding.