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.
ChenW.L.YangW.J.LoH.F.YehD.M.2014Physiology, anatomy, and cell membrane thermostability selection of leafy radish (Raphanus sativus var. oleiformis Pers.) with different tolerance under heat stressScientia Hort.179367375
GuoH.DicksonM.H.HunterJ.E.1991Brassica napus sources of resistance to black rot in Crucifers and inheritance of resistanceHortScience.s2615451547
HallA.E.2001Crop response to environment. CRC Press Boca Raton FL
KanekoY.TakagiC.K.BangS.W.MatsuzawaY.2007Radish p. 141–160. In: C. Kole (ed.). Genome mapping and molecular breeding in plant. Springer Berlin
KitamuraS.1958Varieties and transitions of radish p. 1–19. In: I. Nishiyama (ed.). Japanese radish. Jpn. Soc. Promotion Sci. Tokyo
MasatoT.KeitaS.NakaoK.SatoruM.MasashiH.2005Construction of molecular linkage map of radish (Raphanus sativus L.), based on AFLP and Brassia-SSR markerBreeding Sci.55107111
MuminovicJ.MerzA.MelchingerA.E.2005Genetic structure and diversity among radish varieties as inferred from AFLP and ISSR analysesJ. Amer. Soc. Hort. Sci.1307987
RaymondA.T.G.1985Vegetable seed production. 1st ed. Longman Harlow
YamagishiH.TateishiM.TerachiT.MurayamaS.1998Genetic relationships among Japanese wild radishes (Raphanus sativus f. raphanistroides Makino), cultivated radishes and R. raphanistrum revealed by RAPDJ. Jpn. Soc. Hort. Sci.67526531