In vitro elimination of onion yellow dwarf and shallot latent viruses in shallots (Allium cepa var. ascalonicum L.)

Abstract

Two shallot (Allium cepa var. ascalonicum L.) cultivars, ‘Mikor’ and ‘Jermor’, were used to test a protocol for in vitro virus elimination. Basal explants were prepared, surface sterilised, and placed onto a medium consisting of Murashige and Skoog (M & S) salts and vitamins with the addition of 3% sucrose, 1.0 mg/litre benzyladenine, 50 mg/litre ribavirin, and 0.8% agar. The explants underwent 5–6 days of continuous heat therapy: 4 h light at 35°C; 4 h dark at 31°C. When the shoots were 2–3 cm long they were excised, transferred to shoot inducing medium without ribavirin (the anti-viral chemical), and grown under normal tissue culture conditions of 24°C under fluorescent lights with a photoperiod of 16 h. Finally, the plantlets were introduced to a bulb inducing medium (M & S salts and vitamins, 120 g/litre sucrose, 5 g/litre activated charcoal) for 2 months in vitro before being tested for onion yellow dwarf and shallot latent viruses by ELISA (enzyme-linked immunosorbent assay) and transferred either to the glasshouse or into long-term storage (6°C with a photoperiod of 16 h). Virus assays have confirmed that 60% of resulting ‘Jermor’ and 62.0% of ‘Mikor’ grown in vitro plants were free of shallow latent and onion yellow dwarf virus infections. © 1998 Taylor & Francis Group, LLC.