Hot-water treatment for seeds
Hot water treatment of own seed to prevent seed borne diseases such as black rot, black leg, black spot and ring spot of crucifers is recommended. This treatment helps reduce the seed-borne pathogens such as Alternaria spp., Colletotrichum spp., Phoma spp., Septoria spp., and bacterial pathogens (Pseudomonas spp., and Xanthomonas spp). However, specified temperature and time interval must be strictly followed in order to maintain seed viability. Use a good thermometer or better ask for assistance from qualified personnel from your local extension office. To make sure that the seed is not damaged it is advisable to test the germination of 100 heat-treated and 100 untreated seeds.
For potato tubers heat treatment of 10 min in water at 55degC was used. The same treatment of naturally or artificially contaminated seed tubers gave complete absence of blackleg infection in the field and decreased the amounts of powdery scab (Spongospora subterranea) and black scurf (Rhizoctonia solani) on progeny tubers.
1. In a large pot put plenty of water, heat the water to the required temperature.
2. Place seeds in loose cotton bag and submerge it in water. Follow strictly the recommended temperature and the time required. It is important that the water is maintained at a uniform temperature throughout the container. Constantly stir the water while soaking the bag. Suspend the bag and do not let it touch the bottom of the pot.
3. Remove the bag and cool it in clean cold water to stop the heating.
4. Spread the seeds on a clean dry paper to cool and dry.
5. Preferably do not store treated seeds. Sow them immediately on well-prepared seedbeds.
If treated seeds cannot be sown immediately, a good way to store the seeds is as follows:
- Dry the seeds in the indirect sun until they are completely dry.
- Take a clean jar, pot or bottle of clear non-coloured glass and place a clean piece of cloth with warm ashes in the bottom. You should be able to touch the ashes without burning yourself. Close the container well and let the ashes cool. By adding ashes, any water that gets in the container will be absorbed by the ashes and will prevent the seeds from moulding and rotting
- After an hour or so, the ashes should be cool and you can then place the seeds, loose or wrapped in a transparent plastic bag, in the container. Close the container with a piece of plastic (in case of a bottle with a cork). Spread about 2 mm layer of grease or vaseline over the plastic or cork so that the edges are covered to prevent moisture getting into the container.
- Store the container in a cool, dry place.
- Check regularly if mould has formed on the seeds. If the seeds were dried well, the chance that mould would develop is very small. However, should you see mould, dry the seed again.
Heat treatment recommendations:
Potato tuber: 55degC for 10 min
Spinach, brussels sprouts, cabbage, pepper, tomato, eggplant: 50degC: 30 minutes
Broccoli, cauliflower, carrot, collard, kale, kohlrabi, turnip: 50degC: 20 minutes
Mustard, cress, radish: 50degC: 15 minutes
Lettuce, celery, celeriac: 47degC: 30 minutes
(Nega et al. 2003)