Use of CACTA mobile genetic elements for revision of phylogenetic relationships in Brassica rapa L. species

Abstract

To supplement our previous studies of genetic diversity in Brassica rapa L. by SSR analysis, for the first time, we used Class II transposable elements to clarify the phylogenetic relationships. The core collection of 96 accessions stored at the Vavilov Institute of Plant Industry is used in the study. Experiments with 12 S-SAP primer pairs gave rise to 123 polymorphic markers. Using TE markers, we divide B. rapa crops into two major clusters: East Asian vegetables and Indo-European-Asian oilseed and turnip. The first cluster is divided into the subclusters of pak-choi and bok choi according to botanical classification and the results of SSR analysis. The earlier classification is improved by subclassification of pak-choi into groups, including identification of the separate group of headed cabbages, revision of the positions of the Hiroshimana and Mizuna forms, and subcategorization of oilseed by geographical origin. However, more accurate positions of accessions in the system of the species are obtained by construction of a SAHN dendrogram with 149 SSR and 123 S-SAP markers. The diagram shows that only a few accessions of European turnip are dispersed among the accessions of the other cluster but some accessions form a separate group in the Nepal-Indian subcluster. They are assumed to be the oldest forms closely related to the first domesticated Central-Asian B. rapa form.