Long-lived perennials have lengthy juvenile phases, extensive outcrossing, widespread hybridization, and limited population structure. Under domestication, these features, combined with clonal propagation, multiple origins, and ongoing crop-wild gene flow, contribute to mild domestication bottlenecks in perennial fruit crops. Morphological changes under domestication have many parallels to annual crops, but with key differences for mating system evolution and mode of reproduction. Quantitative trait loci associated with domestication traits in perennials are mainly of minor effect and may not be stable across years. Future studies that take advantage of genomic approaches and consider demographic history will elucidate the genetics of agriculturally and ecologically important traits in perennial fruit crops and their wild relatives.

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84 I. Introduction: evolving concerns over loss of crop diversity 85 II. Defining and measuring crop genetic erosion 89 III. Evidence for, and drivers of, changes in crop diversity over time 92 IV. Steps needed to advance knowledge about crop genetic erosion 99 V. Conclusion: mitigating, stemming and reversing losses of crop diversity 102 Acknowledgements 103 References 104 Appendix A1 111