Tomato seeds must be treated after they are harvested for planting because they are susceptible to a number of seed-borne diseases. If you apply treatment to your tomato seeds immediately after harvesting and before drying them, they will stand the best chance of growing into disease-free adult plants.
Juice the tomato, then fill a container (glass, plastic or ceramic) halfway full with the juice, pulp and seeds. Leave the mixture to ferment at room temperature for four days. Stir it twice daily. Then remove the seeds by filling the container with water repeatedly and scooping off the tomato pulp, seeds and skin that float to the top until you are left with the quality seeds that will be at the bottom of the container. Collect the seeds and wash off any flesh that adheres to them.
Add 1 ounce of pure (99 percent) acetic to 1 gallon of water and stir. Place the seeds in the container and allow them to soak for 24 hours. Stir the solution periodically. At the end of 24 hours, scoop the seeds out with a spoon, place them in another smaller container and rinse them off thoroughly with water before drying them.
Hot Water Treatment
Bring a pot of water (at least five times the volume of your seeds) on the stove to 122 degrees Fahrenheit (use a dairy or laboratory thermometer to measure---it's important that the temperature remain consistent). Then add the tomato seeds and stir the water constantly for 25 minutes, and remove the seeds with a large spoon and dunk them into a waiting bowl of cold water. Stir them for one to two minutes to make sure that they have cooled. Hot water treatment does not control tobacco mosaic virus disease or embryonic bacterial canker. Dust the seed with a tomato-seed fungicide after it has dried.
This chemical soak treatment provides the best protection for tomato seeds that are susceptible to tomato mosaic and other seed-borne viruses. Soak the tomato seed in a 10 percent solution of household bleach or trisodium phosphate for 15 minutes. Or, soak the seed in a 5 percent solution of hydrochloric acid for six hours.
Tomato Seed Protectant
Tomato seed fungicide must be sprayed or dusted (according to the manufacturer's instructions) on acid-treated, chemical-treated or hot-water treated seeds as soon as they have dried. Commonly used seed fungicides are thiram D, captan S and mancozeb S.