Yes, Early Blight ( A. solani) can be seedborne but as long as you process the seeds by fermentation, that removes most of the possible spores that are on the seed coat.

And I say fermentation and no doubt someone will come along and suggest using one of the oxidative methods such as Oxiclean or Comet, bleach is not commonly used for a first treatment, but if you do a search here I think you'll find that there is no data for what is removed from the seed coat using the oxidative methods for tomato seeds.

In any case, we do have the research of Dr. Helene Dillard who had grants from Campbells or Heinz, I can't remember which, that shows that fermentation is effective.

Does it mean that ALL of the primarily fungal pathogens are removed, no it doesn't for that seldom happens but infection of plants is quantitative, so it lessens the probability that treated seeds will transmit disease.

Of those bacterial and vial pathogens that have been checked, they are in the endosperm of the seed so no surface treatment can eliminate them.

Carolyn