Traditional seed production in landraces of daikon (Raphanus sativus) in Kyushu, Japan

Abstract

Landraces of daikon, Japanese radish, Raphanus sativus var. hortensis, are grown and used traditionally in Kyushu, Japan. These landraces are maintained by seeds harvested from selected plants which are transplanted as dormant tap roots or are retained in a portion of field. Seeds kept in intact siliquas on the stems are harvested and stored until use, by hanging the dried stems. Although the relatively small number of plants used in a patch for seed production might be expected to result in a narrow base of genetic diversity of a farmers' lot in a landrace, addition of a few plants with contrasting features, pollen exchange between household patches, and contamination from other cultivars and feral forms may save the landraces from the rapid loss of diversity and deterioration caused by inbreeding depression. The seed production by transplanting described in medieval Japanese literature is relatively similar to the current practice. The factors responsible for maintenance of the landrace together with the cultural and climatic diversity of Japan may have contributed to a high diversity of landraces of the daikon.