Hi CG,
Seed companies disinfect the seeds they sell you using heat treatment using special equipment that prevents over-heating and damaging the seeds. So commercial seeds don't carry a fungal infection. But seeds that you save can and probably do. But no seed treatment can solve your problems, because you have to plant the seed into a growing medium and water it, and as soon as you even handle a seed to plant it, you risk infecting it. The growing medium can contain infectious organisms, and the water or fertilizer that you water the seeds with can also contain infectious organisms. So nothing that you can do to the seeds themselves will solve your problems.
People have tried adding hydrogen peroxide to the water that they moisten the growing medium with, with various degrees of success. I have tried hydrogen peroxide, Physan 20, and commercial systemic antifungals, with various degrees of success, and failure. (I suspect that hydrogen peroxide decomposes Physan 20 and commercial systemic antifungals, so it is best to use those things separately.)
Oxine is what I am using currently, and I am using it alone. It is what I initially water the growing medium with, as well as in all subsequent applications of liquid nutrients. Oxine is effective in very dilute amounts. I am currently using just 1/2 teaspoon of Oxine per gallon of water or liquid nutrients, and that is considered to be a strong Oxine solution. Many users of Oxine deal in just drops per gallon. (My son uses it to prevent disease in the drinking water for his chickens and guineas, at only 4 to 6 drops per gallon.) I have gotten zinnia plants from seeds that were saved from plants that died of disease, so Oxine seems to be very effective. But I think it is too early for me to be recommending that people depend on Oxine to solve their plant problems. I plan to continue using Oxine until I have some kind of noticeable failure with it.
ZM
Q