Oliver White, Manosh Biswas, Wendawek M. Abebe, Yann Dussert, Firew Kebede, Richard Nichols, Richard J. A. Buggs, Sebsebe Demissew, Feleke Woldeyes, Alexander S.T. Papadopulos

Clonal propagation enables favourable crop genotypes to be rapidly selected and multiplied. However, the absence of sexual propagation can lead to low genetic diversity and accumulation of deleterious mutations, which may eventually render crops less resilient to pathogens or environmental change. To better understand this trade-off, we characterise the domestication and contemporary genetic diversity of Enset (Ensete ventricosum), an indigenous African relative of bananas (Musa) and principal starch staple for 20 million Ethiopians. Wild enset is strictly sexually outcrossing, but in cultivation is exclusively propagated clonally and associated with diversification and specialisation into hundreds of named landraces. We applied tGBS sequencing to generate genome-wide genotypes for 192 accessions from across enset’s cultivated distribution, and surveyed 1340 farmers on enset agronomic traits. Overall, reduced heterozygosity in the domesticated lineage was consistent with a domestication bottleneck that retained 37% of wild diversity. However, excess low frequency putatively deleterious missense mutations present as heterozygotes suggested accumulation of mutational load in clonal domesticated lineages. Our evidence indicates that the major domesticated lineages initially arose through historic sexual recombination associated with a domestication bottleneck, followed by amplification of favourable genotypes through an extended period of clonal propagation. Among domesticated lineages we found significant phylogenetic signal for multiple farmer identified food, nutrition and disease resistance traits and little evidence of contemporary recombination. Development of future-climate adapted genotypes may require crop breeding, but outcrossing risks exposing deleterious alleles as homozygotes. This trade-off may partly explain the ubiquity and persistence of clonal propagation over recent centuries of comparative climate stability.