The Begonia seedlings are also doing very well and so far no signs of disease.
Sadly the same cannot be said for the Antirrhinum seedlings. Almost one entire tray has been wiped out by 'Damping Off' and the second tray has also developed a small patch. To try to halt the progress of the disease i have moved the trays to the unheated propagator where the humidity will be much lower. Although a lot of seedlings have been lost, there are still plenty left to fill the garden assuming they all survive.
I have decided to stop top watering the seedlings using a spray applicator and bottom water them only using a flat tray with water, leaving the trays standing in water for a while until they have soaked up enough water. This type of watering appears to have greatly helped the progress of the Impatiens which were becoming a worry a few days ago.
I suspect that the heating of the underside of the trays by the propagator is drying out the lower compost and the top watering has been insufficient to penetrate deeply which has not encouraged the roots to grow downwards quickly enough. I suspect that If i tried to apply sufficient water via spray on the surface this would simply encourage the 'Damping Off'. For the time being i will water all the seed trays by soaking in water.
I set up the propagator i built a few months ago and have planted a 40 cell tray of French Marigold 'Glowing Embers' seeds. The temperature probe has been placed in one of the inside cells and the temperature set to 20 centigrade. The seeds were left over from last year. I expect the seeds to germinate within the next 72 hours. After that i will need to be careful of the risk of 'damping off' killing them.