Background: Crop wild relatives (CWRs) contain genetic diversity, representing an invaluable resource for crop improvement. Many of their traits have the potential to help crops to adapt to changing conditions that they experience due to climate change. An impressive global effort for the conservation of various CWR will facilitate their use in crop breeding for food security. The genus Brassica is listed in Annex I of the International Treaty on Plant Genetic Resources for Food and Agriculture. Brassica oleracea (or wild cabbage), a species native to southern and western Europe, has become established as an important human food crop plant because of its large reserves stored over the winter in its leaves. Brassica cretica Lam. (Bc) is a CWR in the brassica group and B. cretica subsp. nivea (Bcn) has been suggested as a separate subspecies. The species Bc has been proposed as a potential gene donor to brassica crops, including broccoli, cabbage, cauliflower, oilseed rape, etc. Results: We sequenced genomes of four Bc individuals, including two Bcn and two Bc. Demographic analysis based on our whole-genome sequence data suggests that populations of Bc are not isolated. Classification of the Bc into distinct subspecies is not supported by the data. Using only the non-coding part of the data (thus, the parts of the genome that has evolved nearly neutrally), we find the gene flow between different Bc population is recent and its genomic diversity is high. Conclusions: Despite predictions on the disruptive effect of gene flow in adaptation, when selection is not strong enough to prevent the loss of locally adapted alleles, studies show that gene flow can promote adaptation, that local adaptations can be maintained despite high gene flow, and that genetic architecture plays a fundamental role in the origin and maintenance of local adaptation with gene flow. Thus, in the genomic era it is important to link the selected demographic models with the underlying processes of genomic variation because, if this variation is largely selectively neutral, we cannot assume that a diverse population of crop wild relatives will necessarily exhibit the wideranging adaptive diversity required for further crop improvement.

1Crop wild relatives contain great levels of genetic diversity, representing an invaluable resource 2 for crop improvement. Many of their traits have the potential to help crops become more 3 resistant and resilient, and adapt to the new conditions that they will experience due to climate 4 change. An impressive global effort occurs for the conservation of various wild crop relatives 5 and facilitates their use in crop breeding for food security. 6 The genus Brassica is listed in Annex I of the International Treaty on Plant Genetic Resources 7 for Food and Agriculture. Brassica oleracea (or wild cabbage) is a species native to coastal 8 southern and western Europe that has become established as an important human food crop 9 plant because of its large reserves stored over the winter in its leaves. 10 Brassica cretica Lam. is a wild relative crop in the brassica group and B. cretica subsp. nivea has 11 been suggested as a separate subspecies. The species B. cretica has been proposed as a 12 potential gene donor to a number of crops in the brassica group, including broccoli, Brussels 13 sprout, cabbage, cauliflower, kale, swede, turnip and oilseed rape. 14 Here, we present the draft de novo genome assemblies of four B. cretica individuals, including 15 two B. cretica subsp. nivea and two B. cretica. 16 De novo assembly of Illumina MiSeq genomic shotgun sequencing data yielded 243,461 contigs 17 totalling 412.5 Mb in length, corresponding to 122 % of the estimated genome size of B. cretica 18 (339 Mb). According to synteny mapping and phylogenetic analysis of conserved genes, B. 19 cretica genome based on our sequence data reveals approximately 30.360 proteins. 20 Furthermore, our demographic analysis based on whole genome data, suggests that distinct 21 populations of B. cretica are not isolated. Our findings suggest that the classification of the B. 22 cretica in distinct subspecies is not supported from the genome sequence data we analyzed. 23 24 25 26