Of all the seeds that germinated, just one seedling grows well. The others got badly affected by mildew. Some already died, but I will still give the others a chance to recover.
A few days ago, after a 48 hours soak and a supplementary Oxonia bath, I put the R. webbiana seeds I became from KBW Organic (http://www.helpmefind.com/rose/l.php?l=21.295653) in wet masonry sand in the fridge at 1°C. Two months from now, I'll sow them.