Resource Manual on Integrated Production and Pest ... - julitoaligaen

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<strong>Resource</strong> <strong>Manual</strong> on IPPM in Vegetable World Education Philippines, Inc. E. Seed Treatments Two reasons to treat seeds 1. To control diseases attached to or inside the seed (seed-borne diseases), 2. To protect seeds against diseases in the soil that can attack seeds, emerging roots or young seedlings (soil-borne diseases). Seed-borne Diseases Seed can become infected with fungal spores or bacteria (seed-borne diseases). Infection can accur during the growing season, when seed is still on the plant or it may occur after the seed has been extracted from the plant. Common seed-borne diseases of tomato are early blight (Alternaria solani), Tobacco Mosaic Virus (TMV) and fungal wilt (Fusarium and Verticulum). Soil-borne Diseases Seed can also become infected after it has been sown in the soil. Fungi or bacteria living in the soil may attack the seed and cause death of the seed or the emerging roots even before the seedling has emerged above the soil (soil-borne diseases). A common soilborne disease affecting seed and seedlings is damping-off, caused by a complex of fungi. When to Treat? When seed is bought from reliable seed companies, it will usually be disease-free. When seed is locally produced, it is probably better to sterilize it before sowing. When soil has causes problems with damping-off disease before, it can be helpful to coat seed before sowing. Seed Treatment Methods There are four main methods for seed treatment: 1. Physical by soaking in hot water 2. Chemical by sterilizing seed with chemicals or coating seed with a layer of fungicide. 3. Botanical by coating seed with a layer of plant extract. 4. Biological by coating seed with a layer of antagonistic fungi. None of these treatments will completely prevent attack in all circumstances. In addition to seed treatment, it is important to select a field that is free of soil-borne disease. Some management practices for soil-borne diseases include crop rotation and the use of resistant or tolerant varieties. 188
<strong>Resource</strong> <strong>Manual</strong> on IPPM in Vegetable World Education Philippines, Inc. Hot Water Seed Treatment To kill fungal spores or bacteria attached to or within the seed, seed should be soaked in hot water at 50 O C for 30 minutes. The right water temperature and the right duration for seed treatment are very important. If the water is too cold, the pathogens are not killed. If the water is too hot, seed germination will be strongly reduced. The easiest way to treat seed is to prepare water of 50 O C on a small fire or burner. Carefully check water temperature with a thermometer. Pour the 50 O C water into a thermos flask and add seed. It may be easy to wrap the seeds in a cloth to keep them together. Leave the seed in the flask for 30 minutes. After soaking in hot water, the seed is placed in clean, boiled water already cold, to cool down the seed. Dry by spreading the seed in a thin layer on paper or cloth. In some cases, a fungicide coating is applied after hot-water treatment. Chemical Seed Treatment Many seed companies use chemical treatments, such as sodium hypochlorite or sodium phosphate, to sterilize the surface of the seed. Next to this, seed can be coated with a fungicide. This fungicide can sometimes be seen on the seed as a colored coating. The fungicide used is listed on the seed package. The fungicide can kill spores of diseases. Chemical fungicides for seed protection are relatively inexpensive and cause little environmental damage since they are used in small amounts. However, they are effective only for a short time (at most one month) and they do not spread through the soil with the root system. Unfortunately, chemical seed sterilization cannot guarantee that the seed is completely disease free. This is because some pathogens are present inside the seed. An example is TMV where the virus can be present both on and in the seed coat. Chemicals only sterilize the surface of the seed and do not reach infections inside the seed. Hot water treatment may sometimes be more effective to control pathogens inside seed. Botanical Seed Treatment Seed can be protected from soil-borne fungi and from cutworms by a coating of a botanical extract such as crushed garlic. Garlic is well known for its strong odor which has repellent effect on insects and birds, and it can prevent diseases. The garlic is thoroughly crushed to obtain juice and pulp. Seed is mixed with this extract. The seed can be immediately sown after this treatment, or left to dry. Biological Seed Treatment Seed can also be protected with a coating of biological agents. These are usually antagonistic fungi or bacteria that work against soil-borne pathogens. Examples are the antagonist fungus Trichoderma sp. and the bacterium Bacillus subtilis, which are sometimes mixed with a chemical fungicide for commercial seed treatment. 189
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Page 3 and 4: Compiled and published by: World Ed
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Resource Manual on Integrated Production and Pest ... - julitoaligaen

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