Radish

Abstract

Radish, Raphanus sativus L., is an annual vegetable of the family Cruciferae. The genus Raphanus originated in the regions from the Mediterranean to Black Sea and was classified under two sections of Rapha-nis DC. and Hesperidopsis Boiss. These two sections comprise six species including Raphanus sativus, R. raphanistrum, R. microcarpus, R. rostras, R. landra and R. maritimus, and one species Raphanus aucheri, respectively (Kitamura 1958). Kitamura (1958) also assumed that R. sativus could be developed around the Mediterranean region by natural or artificial crossing between R. landra and R. maritimus. Banga (1976) and Hida (1990) presumed that four wild species (R. raphanistrum, R. maritimus, R. landra and R. ros-tras) could be involved in the origin of radish. From a study on the wild R. sativus and R. raphanistrum by Panetsos and Baker (1967), the differentiation of two species was confirmed. The wild R. sativus has distinguished features including a white flower or partially purple flower on a white background, and a tender and slightly thick pod made up of spongy parenchyma. On the other hand, R. raphanistrum has a yellow flower, and slender and hardy pod. The fully ripened pods break into pieces. In California, the above two species were growing with intermediate types that could originate from natural hybridization between them. The F 1 plants induced by artificial crossing between the two species showed intermediate features, chromosome configurations of 1IV+7II at first metaphase (MI) of pollen mother cells (PMCs) and moderate fertility of 50% in both pollen formation and seed setting. From these facts, it was suggested that the F 1 plants were carrying some reciprocal translocations in one pair of chromosomes. When the wild R. sativus type was naturally backcrossed with cultivated radish, some progenies did not form the quadrivalent chromosomes , and showed high seed setting. Therefore, it was suggested to induce gene flow (or introgression) from R. raphanistrum to radish cultivars. Eber et al. (1994, 1998) also confirmed these facts by the analysis of hybrids between the native R. raphanistrum and cultivated R. sativus in France. On the other hand, Kato and Fukuyama (1982) observed normal chromosome configuration of 9II in meiosis and high seed setting in F 1 hybrids between R. sativus and R. raphanistrum L. ssp. landra. From these results, it was assumed that the chromosomal reconstruction might happen even in R. raphanistrum.