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Article|01 Apr 2022|OPEN
Evidence for two domestication lineages supporting a middle-eastern origin for Brassica oleracea crops from diversified kale populations
Chengcheng Cai1,2 , Johan Bucher1 and Freek T Bakker3 , Guusje Bonnema,1 ,
1Plant Breeding, Wageningen University and Research, Wageningen, The Netherlands.
2Graduate School Experimental Plant Sciences, Wageningen University and Research, Wageningen, The Netherlands
3Biosystematics Group, Wageningen University and Research, Wageningen, the Netherlands
*Corresponding author. E-mail: guusje.bonnema@wur.nl

Horticulture Research 9,
Article number: uhac033 (2022)
doi: 10.1038/hortres.2022.uhac033
Views: 354

Received: 20 Sep 2021
Revised: 10 Apr 2022
Accepted: 26 Dec 2021
Published online: 01 Apr 2022

Abstract

Brassica oleracea displays enormous phenotypic variation, including vegetables like cabbage, broccoli, cauliflower, kohlrabi, kales etc. Its domestication has not been clarified, despite several genetic studies and investigations of ancient literature. We used 14 152 high-quality SNP markers for population genetic studies and species-tree estimation (treating morphotypes as “species”) using SVD-quartets coalescent-modelling of a collection of 912 globally distributed accessions representing ten morphotypes of B. oleracea, wild B. oleracea accessions and nine related C9 Brassica species. Our genealogical tree provided evidence for two domestication lineages, the “leafy head” lineage (LHL) and the “arrested inflorescence” lineage (AIL). It also showed that kales are polyphyletic with regards to B. oleracea morphotypes, which fits ancient literature describing highly diverse kale types at around 400 BC. The SVD-quartets species tree topology showed that different kale clades are sister to either the LHL or the AIL. Cabbages from the middle-east formed the first-branching cabbage-clade, supporting the hypothesis that cabbage domestication started in the middle-east, which is confirmed by archeological evidence and historic writings. We hypothesize that cabbages and cauliflowers stem from kales introduced from Western Europe to the middle-east, possibly transported with the tin-trade routes in the Bronze age, to be re-introduced later into Europe. Cauliflower is the least diverse morphotype showing strong genetic differentiation with other morphotypes except broccoli, suggesting a strong genetic bottleneck. Genetic diversity reduced from landraces to modern hybrids for almost all morphotypes. This comprehensive Brassica C-group germplasm collection provides valuable genetic resources and a sound basis for B. oleracea breeding.