title: Population Structure and Phylogenetic Relationships in a Diverse Panel ofBrassica rapaL.
abstract: The crop speciesBrassica rapaL. has significant economic importance around the world. However, the global distribution and complex evolutionary history of the species has made investigating its genetic population structure difficult. Crop domestication and improvement has resulted in extreme phenotypic diversity and subspecies that are used for oilseed, food for human consumption, and fodder for livestock. These subspecies include the oilseed morphotypes.oleifera(turnip rape), ssp.dichotoma(brown sarson/toria), ssp.trilocularis(yellow sarson); ssp.rapa(turnip); and Asian leafy vegetables ssp.pekinensis(Chinese cabbage), ssp.chinensis(bok choy), ssp.nipposinica(mizuna/mibuna), ssp.rapifera(rapini/broccoli rabe), ssp.narinosa(tatsoi), sspparachinensis(choy sum), and ssp.perviridis(komatsuna). To date, studies have had insufficient sampling to determine the relationship of all morphotypes, especially oilseed morphotypes, and questions remain over the contribution of morphotype and geographic origin to population structure. We used genotyping-by-sequencing to score 18,272 single nucleotide polymorphism markers in a globally diverse panel of 333B. rapaNational Plant Germplasm System accessions that included 10 recognized subspecies. Our population genetic and phylogenetic analyses were broadly congruent and revealed five subpopulations that were largely reflective of morphotype and geography. These subpopulations were 1. European turnips/oilseed, 2. Asian turnips/oilseed, 3. yellow/brown sarson (ssp.trilocularisand ssp.dichotoma), 4. Chinese cabbage (ssp.pekinensis), and 5. bok choy, choy sum, and tatsoi (ssp.chinensis, ssp.parachinensis, ssp.narinosa). Additionally, we found evidence of polyphyly and/or paraphyly, particularly for oilseed morphotypes (ssp.oleiferaand ssp.dichotoma) and turnips. The results of this study have provided improved resolution to the genetic and phylogenetic relationships of subspecies within the speciesB. rapa. Understanding of these relationships is key to the future genetic study and improvement of this globally important crop species.
authors.affiliation: Division of Biological Sciences, University of Missouri Columbia, MO, USA.
authors.forename: Kevin A
authors.initials: KA
authors.lastname: Bird
authors.affiliation: Division of Biological Sciences, University of MissouriColumbia, MO, USA; National Key Lab of Crop Genetic Improvement, Huazhong Agricultural UniversityWuhan, China.
authors.forename: Hong
authors.initials: H
authors.lastname: An
authors.affiliation: Plant Breeding and Genetics Section, School of Integrative Plant Science, Cornell University Ithaca, NY, USA.
authors.forename: Elodie
authors.initials: E
authors.lastname: Gazave
authors.affiliation: Plant Breeding and Genetics Section, School of Integrative Plant Science, Cornell University Ithaca, NY, USA.
authors.forename: Michael A
authors.initials: MA
authors.lastname: Gore
authors.affiliation: Division of Biological Sciences, University of Missouri Columbia, MO, USA.
authors.forename: J Chris
authors.initials: JC
authors.lastname: Pires
authors.affiliation: Plant Genetic Resources Unit, United States Department of Agriculture-Agricultural Research Service Geneva, NY, USA.
authors.forename: Larry D
authors.initials: LD
authors.lastname: Robertson
authors.affiliation: Plant Genetic Resources Unit, United States Department of Agriculture-Agricultural Research Service Geneva, NY, USA.
authors.forename: Joanne A
authors.initials: JA
authors.lastname: Labate
keywords: Brassica rapa; diversity panel; genotyping-by-sequencing; phylogenetic analysis; population structure