The use of corms produced under storage at low temperatures as a sourceof explants for the in vitro propagation of saffron reduces contaminationlevels and increases multiplication rates

Abstract

Saffron is a triploid sterile crop with a low vegetative propagation rate, which prevents the widespread use of selected genotypes. Despite efficient in vitro propagation via direct organogenesis being very interesting, high contamination levels and low propagation rates preclude the commercial use of this technique. In order to obtain a source of explants for the in vitro multiplication of saffron that allows low contamination levels and efficient propagation, daughter corms were produced by storing non-planted mother corms at low temperatures (1-3 degrees C) for 9 months. This method avoids field cultivation and yields more corms than field production (8 vs. 3 corms per mother corm). Corms produced under cold storage conditions were in vitro sprouted on media with a high level of cytokinins (5 mg l(-1) 6-benzylaminopurine or 1 mg l(-1) thidiazuron) and 0.5 mg l(-1) naphthalene acetic acid, and sprouted buds were cultivated on the same media. After 8 weeks of culture, multiple shoot primordia emerged from the base of the sprouted buds with no callus formation, and up to 400 shoot primordia were produced from one initial mother corm. These shoot primordia can be elongated and 90% produce corms. The high multiplication rate, lack of contamination, and the fact that multiplication occurs through direct organogenesis make the method suitable for the propagation of selected genotypes. Otherwise shoot clusters can be maintained for 6-7 months. However for longer maintenance periods, shoot proliferation capacity by direct organogenesis diminishes, and the emergence of somaclonal variation cannot be ruled out.