|Low-external Input Rice Production (IIRR, 292 p.)|
Knowing the quality of rice seed will enable one to decide the appropriate practices that could help maintain or improve the performance of seedlots.
Seeds on hand can be tested for the following:
1. Dryness. Most seeds, including rice, store better when dry. High moisture level could result to heating, further accumulation of moisture, active growth of storage insects and fungi and even unwanted germination. Seeds which have not been properly dried are also damaged during processing.
- Sundrying for 3-5 days is often sufficient to bring the moisture content of the freshly harvested seeds down to the safe level (13% or less). If the seeds have been stored for quite some time or were obtained from other sources, dryness could be checked by biting the seeds. If brittle, the moisture content is 13% or less the desired moisture for planting or storage. The biting test should not be done if seeds have been treated with chemicals. If not sure, simply redry the seeds for 1-2 days.
2. Purity and Seed Health. Impurities, such as weed seeds, other crop seeds, other vegetative parts and inert matter, should be removed. These could serve as hosts of crop pests and seed-transmitted diseases or affect seed (and seedling) performance in the field or in storage. Weed seeds could germinate in the field and add to the existing weed population. Seeds of other cultivars, when present, could also lead to genetically impure seedlots.
Purity and Seed Health
- Examine the seedlot for impurities, diseased seeds (symptoms are discoloration and presence of fungal bodies) and infested seeds (seeds with holes or are partially eaten by insects, presence of eggs/egg mass or larva).
- If a large proportion of the sample consists of impurities, the seedlot should be cleaned prior to storage or planting. Cleaning can be done by winnowing or soaking the seeds in water. Defective seeds, weed seeds and other inert matter float to the surface, while seeds that sink are of higher density and are usually of better quality.
- If the seedlot contains a large proportion of seeds of other cultivars, some form of manual sorting must be done before storage or planting, unless the mixture was intentional.
- Seedlots which contain a large proportion of diseased or infested seeds are not recommended for storage or planting. If the proportion of diseased or infested seeds is minimal, remove such seeds if possible and soak the rest of the seedlot in hot water (5256°C) for 5 minutes (if seeds are wet) or 10 minutes (if seeds are dry).
- Other diseases which do not readily show visible symptoms can be detected only by using special techniques. If these diseases are suspected, have the seeds certified for health at the Bureau of Plant Industry or do not use them for planting. Chances of developing diseases in the succeeding crops are minimized if seeds are harvested from healthy plants and healthy surroundings.
3. Seed Germination and Seedling Health. Germination results could serve as a guide as to whether the seeds could or should still be stored, immediately planted or discarded. Also, they give an idea as to how much seed is required for planting. Seeds with low percentage germination will not keep long and will produce less vigorous plants.
- Sow the pure seeds sampled from the seedlot in moist, clean, absorbent cloth or paper. Roll the cloth or paper loosely (ragdoll method) or keep it on a flat surface covered with the same material.
Seed Germination and Seedling Health
Keep the medium constantly moist by watering, taking care not to flood it. Too much water encourages mold and bacterial growth. Alternatively, seeds could be kept moist by carefully dipping the rolled medium in a pail of water, then putting it in a partially opened plastic bag. Keep seeds being tested in the shade and away from mice, ants and rain.
Keep the medium constantly moist
Good germination, good vigor
Poor germination, poor vigor
- Count normal seedlings after 4-5 days. Percentage germination is calculated as
% germination = No. of normal seedlings/Total no. of seeds tested x 100
- If germination is below 80%, but above 60%, use more seeds. Do not use or store seeds if germination percentage is below 60%.
- Observe for seed vigor since germination results alone could not fully predict the performance of seeds especially under stressed conditions. A seedlot with seeds that emerged rapidly and uniformly is considered more vigorous than one with slow and non-uniform emergence and growth, even if germination percentages are comparable.
- Growing seedlings should also be examined for lesions, spots, blighting (general death of tissue) and streaking. These are symptoms of potentially serious crop diseases. Treat germinated seedlots showing these symptoms in the same manner as seeds found to be infected or infested.