The radish (Raphanus sativus L.), a temperate annual crop of the Cruciferae family originating from East Asia and the Mediterranean, is a popular vegetable worldwide and is rich in iron, calcium, and vitamin B (Kitamura, 1958). It has been ecologically classified into five varieties. Among them, Raphanus var. longipinnatus Bailey (root radish), Raphanus var. radiculus DC. (cherry radish), and Raphanus var. oleifermis Pers. (leaf radish) are commonly consumed as fresh food (Kaneko et al., 2007; Yamagishi et al., 1998). The optimal growth temperature for most radishes lies at 24 °C, with fleshy storage organs reducing in size at higher temperatures (Suzuki, 1978).
Objectives in radish breeding have focused on ecological traits, such as environmental stress tolerance, disease resistance, bolting resistance, cultivating practical adaptability, and consumptive requirement (Kaneko et al., 2007; Masato et al., 2005). Increasing temperature is a critical problem for radish production in Taiwan, especially during the summer season. High temperatures lead to an array of anatomical, morphological, physiological, and biochemical changes in certain crops, including radishes, which affect their growth and development, ultimately resulting in drastic yield reduction (Hall, 2001; Wahid et al., 2007). Thus, the development of heat-tolerant radishes has the potential to provide a long-term solution for coping with a warming environment, especially in Taiwan and other regions with subtropical and tropical climates (Kuo, 1999).
Because of its self-incompatibility, radish is cross-pollinated, which results in a high level of genetic variation (Muminovic et al., 2005). During breeding, mass selection is generally inefficient, and pure-line selection frequently results in inbreeding depression and sterility. However, maternal-line selection (MLS), a modified application of mass selection, is an effective breeding method for the improvement of local varieties for certain environmental adaptations (Raymond, 1985).
The Taichung Agricultural Research and Extension Station (TDARES) announces the release of the ‘Taichung No. 2’ radish, an open-pollinated cultivar for fresh root production. This cultivar was developed using a series of MLSs, evaluated using both field and physiological performances. Radish ‘Taichung No. 2’ is highly heat tolerant with a great root quality and can be sown from April to October in tropical Taiwan.
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