Wild Avocado (Persea americana) Herbarium Genomes Provide Key Insights into Its Wild Population Structure and Domestication History
Abstract
Avocados (Persea americana) are highly nutritious fruits that dominate the global export market and have an extensive genomics research background. They have a complex domestication history with some disagreement on the origins of the three common cultivar varieties (var. drymifolia, var guatemalensis, and var. americana), and most studies have not comprehensively examined the germplasm of wild populations. Our objectives for this study were to better understand how wild avocado populations are structured in the absence of human interference and to assign geographic regions to the origins of domesticated varieties. We sequenced at low coverage the genomes of 25 putatively wild herbarium avocado leaves collected in the last 60 years and spanning their entire native geographic range. We used bioinformatic analyses that examine genotype likelihoods to compare and contrast the population structure of our wild avocados with that of a previously published cultivar dataset. Wild avocados are most likely structured in two distinct populations, one in Central Mexico and one spanning from Chiapas to as far as Peru, and we predict the valley between the Sierra Madre del Sur and the Sierra Madre de Chiapas acts as a reproductive barrier. Overall, wild avocado populations are more genetically differentiated and more diverse compared to cultivars. We attribute the difference to the domestication process which acts to erode genetic variation over time and then reduce differences between varieties through commercial hybridization. In regards to which herbarium specimens have higher genetic affinity to the three common cultivar varieties, our findings support claims that each variety has distinct and separate domestication origin throughout Central America. We also offer a new model fitting our data that includes a single domestication event in Honduras that gives rise to both the var. guatemalensis and var. americana. We encourage more research including the genomes of ancient specimens to help support or refute this scenario.
Citation
Wann, Kevin W (2023). Wild Avocado (Persea americana) Herbarium Genomes Provide Key Insights into Its Wild Population Structure and Domestication History. Master's thesis, Texas A&M University. Available electronically from https : / /hdl .handle .net /1969 .1 /199031.