Genetic Relationships of Heirloom Turnip (Brassica rapa) Cultivars in Shiga Prefecture and Other Regions of Japan

Abstract

In Japan, many turnip (Brassica rapa) cultivars are known as heirloom vegetables, especially in Shiga Prefecture, which is close to the old capital of Japan, Kyoto. Of these, ‘Omikabu’, an heirloom white turnip cultivar in Shiga Prefecture is referred to as the ancestor of the white turnip cultivars, ‘Shogoinkabu’, ‘Tennojikabu’, and ‘Yoriikabu’. Many “red turnip” cultivars that are red or purple-skinned varieties (and sometimes with colored flesh and petioles), also grow in Shiga Prefecture, and are mainly processed into pickled vegetables. However, their origins have not yet been fully verified. In this study, construction of neighbor-joining phylograms and population structure analyses were performed based on eight simple sequence repeat markers for white and red turnips, plus two non-turnip B. rapa vegetables (Chinese cabbage and mizuna). For the white turnip-related lines, a claim that ‘Shogoinkabu’, ‘Tennojikabu’, and ‘Yoriikabu’ are derived from ‘Omikabu’ could not be supported in this study because ‘Omikabu’ lines were separated from the above three cultivars in the phylogram. In contrast, an ‘Omikabu’ line, ‘Omikabura RU’, formed a cluster with ‘Jonansensuji mizuna’, suggesting a genetic relationship (a crossing in the past) between them. For red turnips, close placements of ‘Kisobenikabu’-‘Shinshukabu’, ‘Hinona’-‘Kitanoshokabu’, and ‘Biwakobenikabu’-‘Yurugikabu’ were found in the phylogram, each of which was in good agreement with the proposed cultivar’s origin. The data in this study provide useful information for understanding the genetic relationships among Japanese heirloom turnip cultivars.