Anup Kumar Pandey, Amity University Kolkata
The most emblematic perennial crop of the Mediterranean region is olive. Currently, two taxonomic varieties are recognized, namely var. europaea and wild var. sylvestris. Both the taxonomic varieties have got long lifespan especially the Juvenile phase that can last as long as 15 years in natural conditions. The biggest evidence of domestication of wild varieties of all having found in the eastern MB. According to archaeological and genetic studies, it was found that the domestication of olives took place around 6000 years ago. The reconstruction of the plastid lineage has led to the production of unsolved phylogeny due to low plastid diversity. To find out the evidence of genetic admixture in the distantly related species of olive, a group of newly sequenced and available genomes was analyzed using phylogenomics and population genomics framework. In order to find out the demographic history of olive trees, Approximate Bayesian Computing (ABC) models have been applied.
The ABC models highlighted the paramount role of admixture responsible for the diversity of the crop. In cultivars from the central MB, this feature was particularly predominant, with 20% of the genetic diversity of olives. This may have been acquired through introgression with local wild populations. The existence of a major center of domestication for olives in the Levant has been proven by genetic and archeological sources. However, questions like the extent of admixture and the potential for secondary centers of domestication elsewhere in the Mediterranean Basin persist. Intending to gain novel insights into this question and the recent most evolution of the cultivated olive tree, the scientists sequenced 12 accessions. These accessions include 10 representative cultivars, 1 wild individual of var. sylvestris, and 1 individual from O. europaea subsp. Cuspidata was used as a distant outgroup in their analysis. To capture the signal of the divergent genetic clusters that have been reported by previous studies among the germplasm of the cultivated olive, the 10 cultivars were selected.
The annotation and assembly of the genome that worked as a reference genome, newly sequenced genomes of twelve individuals were improved. A continuous process of olive tree domestication that involved major domestication events which finally led to the recurrent genetic admixture with the wild populations across the Mediterranean basin has been proven by phylogenomic and population structure analysis. The wild variety of olive trees showed much genetic diversity than the cultivated variety. Also, the genes responsible for stress response was positively selected in the cultivated crops. The results conclude the primary domestication of olive trees in the eastern region of the Mediterranean basin was followed by many events across the countries of Southern Europe and northern Africa. This led to genetic admixture with genetically rich populations that were mainly from the western part of the Mediterranean basin.
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References :
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Tuskan GA, Difazio S, Jansson S, Bohlmann J, Grigoriev I, Hellsten U, et al. The genome of black cottonwood, Populus trichocarpa (Torr. & Gray). Science. 2006;313:1596–604. https://doi.org/10.1126/science.1128691.
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