The effect of anti-viral thermal treatments on germination of lettuce (Lactuca sativa) seeds and subsequent seedling development

Experiments on the effects of virus-inactivating high-temperature (40d?C) treatments (thermotherapy) of lettuce seeds partially imbibed in polyethylene glycol solution on subsequent germination and seedling development are described. Precise temperature control is shown to be important and subsequent recovery periods at lower temperature (20d?C) may be beneficial. Fungal contamination which developed on seeds during thermotherapy was controlled, in some seedlots, by treatment in sterile conditions. The fungi were saprophytic on seeds killed by the thermotherapy. Old seed, even with high viability, was more susceptible to heat damage than fresh seed, and even fresh seed may be pushed close to its limits of tolerance by a 10-day treatment. The techniques described may be suitable for producing small numbers of virus-free plants for experimental or breeding purposes.