Genetic divergence of turnip (Brassica rapa L. em. Metzg. subsp. rapa) inferred from simple sequence repeats in chloroplast and nuclear genomes and morphology

Turnip (Brassica rapa L. em. Metzg. subsp. rapa), which is considered to be a primitive type of cultivated B. rapa, is cultivated worldwide as vegetable and fodder. To elucidate the phylogenetic relationships of Eurasian turnips, we examined their morphology and analyzed 6 cpSSR and 18 nuSSR loci in 87 accessions. Examination of seed coat mucilage and leaf hairs revealed existence of geographic distinctions. Two haplogroups were categorized among 12 haplotypes identified by the analysis of cpSSRs and two clusters were detected based on nuSSRs. These haplogroups and clusters were different between eastern and western Eurasia. Although morphological differences were detected between eastern and western Japan, no clear differences of haplotypes and clusters were found in Japanese turnips. Accessions from continental Asia showed various haplogroups and clusters and higher levels of genetic diversity than those from other regions. These results, in addition to previous studies suggest that central Asia is the sole geographic origin of turnips that Asian turnips did not originate as descendants of European turnips, and that almost all Japanese turnips were derived from central Asia.