IN-VITRO ELIMINATION OF ONION YELLOW DWARF AND SHALLOT LATENT VIRUSESIN SHALLOTS (ALLIUM-CEPA VAR. ASCALONICUM L.)

Two shallot (Allium cepa var. ascalonicum L.) cultivars,'Mikor' and 'J ermor', were used to test a protocol for in vitro virus elimination. B asal explants were prepared, surface sterilised, and placed onto a med ium consisting of Murashige and Skoog (M & S) salts and vitamins with the addition of 3% sucrose, 1.0 mg/litre benzyladenine, 50 mg/litre ri bavirin, and 0.8% agar. The explants underwent 5-6 days of continuous heat therapy: 4 h light at 35 degrees C; 4 h dark at 31 degrees C. Whe n 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 degrees C under fluoresc ent lights with a photoperiod of 16 h. Finally, the plantlets were int roduced to a bulb inducing medium (M & S salts and vitamins, 120 g/lit re sucrose, 5 g/litre activated charcoal) for 2 months in vitro before being tested for onion yellow dwarf and shallot latent viruses by ELI SA (enzyme-linked immunosorbent assay) and transferred either to the g lasshouse or into long-term storage (6 degrees 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 an d onion yellow dwarf virus infections.