Effect of thermotherapy and meristem-tip culture on production of virus-free garlic in Chile

Garlic cultivars for crop production in Chile are infected with onion yellow dwarf virus (OYDV), (Bruna et al., 1992). In order to produce virus-free garlic, thermotherapy and meristem-tip culture trials were carried out. In a first trial, garlic cloves cultivar Rosado-INIA were preconditioned at 30 degrees C for 7 days and then treated at 38 degrees C for 38 days in environmental growth chambers. The control cloves were incubated at 20 degrees C for 45 days. Meristem tips around 0,5 to 0,8 mm in diameter were excised and grown in medium containing macronutrients of B-5 (Gamborg et al., 1968) and the micronutrients and vitamins of M &. S (Murashige et al., 1962). Three months later the plantlets were transplanted to greenhouse and indexed by ELISA. (Clark et al., 1977). 65% of garlic plants regenerated from explants were free from OYDV. When infected cloves were subjected to thermotherapy at 38 degrees C before tissue culture, 100 % of the plants were OYDV-free. In a second trial, garlic cloves were subjected to thermotherapy at 38 degrees C for different periods of time (48-54-60-67 and 75 days) and then indexed by ELISA. This was compared with garlic cloves preconditioned at 30 degrees C for 7 days before being exposed to 38 degrees C for the same periods of time already described. The percentage of virus-free garlic plants increased from 38 with 48 days at 38 degrees C to 100% with 75 days at 38 degrees C. The percentage of plants alive decreased from 95% on the 48 days treatment to 62% on the 75 day's treatment. Preconditioning was not necessary under our environmental conditions.