Agreed with Russ that one should be cautious in "sterilizing" potting
media. The clean slate so created invites all comers, from beneficial to
pathogenic. Better to pasteureize at lower temps to redue the chance of
catastrophic outbreaks. For seeds I use a mix of perlite, coarse builder's
sand and an off-the-shelf organic component like peat or Edna's at roughly
2:1:2 respectively. Some fine charcoal is also beneficial. None of these is
exactly sterile but they are clean enough. It is impossible to know if
outbreaks of pathogens are in the soil to begin with or have blown in from
afar.

Dylan