I'll try to answer to some of the questions Luca Comai did in realtion to
the sterilization method using a microwave oven.
i) You do need to put the water inside. In my lab, a couple of microwave
ovens have been broken when users have forgotten to put it in.
ii) You can treat your seeds longer. I did it for 12 min (2 treatments)
This is due to the fact you can not trust the output energy your microwave
brochure is indicating. Even the distribution of the waves are not uniform
inside the oven, and varies in the different brands.
iii) I do not know why, but I had better results when microwaving into the
plastic tubes (close the cap not too tight to let the air escape). I did
try the paper method before. Paper get some of the energy, and it can even
run into fire!
So the conclusion is: you need to optimize the method for YOUR oven by
treating at different times your seeds. Again I have to remain you that
maybe you have a hard contaminant I don't.