Seed viability
Due to tremendous increase in the human population and corresponding increase in daily needs, forests are shrinking in their extend and volume. Further, the reckless cutting of forests has deteriorated the environmental conditions. Many programmes have been launched by Government agencies to recoup the forested conditions in the form of re-forestation and afforestation. In this connection many forest nurseries have been developed to raise seedlings of forest tree species. For producing healthy seedlings, knowledge of seed quality and vigor is an prerequisite.
Knowledge of morphology, weight and other structural features of seeds are the basic requirements to study germination. Germination potential is perhaps the most important measurement in seed testing to determine the viability of seeds as it varies on account of habitat, species and seed source. This potential can be evaluated directly by germination seeds under predetermined conditions and indirectly by biochemical staining, embryo excision, electrical conductivity and IDS (incubation-drying separation) methods. Irregular and often infrequent seed protection of seed species necessities seed storage. Also on the basis of seed life span, many species have been classified as orthodox and recalcitrant. The former can be stored at low temperatures with low moisture content for a longer period whereas the latter cannot be stored for a long time as they cannot be dried to low moisture content. Therefore, the storage physiology of seeds is the foremost requirement before the decision of seed storage is made.
Dormancy is another factor that affects seed germination. There are possibilities that vital seeds do not germinate when tested and can, therefore, be rejected due to lack of knowledge pertaining to dormancy. In such cases, dormancy has to be removed by mechanical, chemical, stratification, and other methods.
Viability
The viability of seeds can be determined by the methods described below:
Cutting test:
The seeds are cut longitudinally into halves by scalpel and count the seeds (without embryo).
IDS test:
Soak the seeds in water at room temperature for 16 hours,then spread out between two moistened bolting paper sheets and keep in this condition in an incubator for 56 hrs at 15°C, 100% relative humidity and 1000 lux illumination. Seeds are to be surface dried for 12 hrs at 15°C. Germination of floating and sinking seeds are to be studied separately.
Topographical tetrazolium staining test:
Soak the seeds in water for required time (variable according to species) at room temperature. Remove the seed coat and then are cut into two halves and immerse in 10% solution of 2, 3, 5 triphelny tetrazolium chloride (pH 6.5-7.0). Leave the seeds in this solution in darkness for staining 35°C. After treatment, wash the seeds with running water to remove extra dye and are transferred to glazed glass for staining studies.
Indigo carmine test:
Soak the seeds in water for 16 hours at room temperature, bisect, longitudinally, and treat with 1:1000 solution (w/v) of indigo carmine for 1 hour at room temperature. The evaluation of seeds is done as in the tetrazolium staining test.
Excised embryo test:
The excision of embryo is done after inhibition. Embryo is removed 8under sterilized conditions and placed on the filter paper under normal conditions of light and moisture at 25°C. Germination is recorded after 14 days.
Electrical conductivity test:
Two replicas of seeds (50×2) are normally taken for this study after each seed sample is weighed unto two decimal points. Place the seeds in a beaker. Cover the beaker after adding distilled water (250ml) to reduce evaporation and contamination by dust. All beakers are to be kept at 20°C for 24 hours. Seeds are separated from water by passing through a course sieve. Determine the electrical conductivity by Conductivity Meter 304.
Germination test:
Keep the seeds on moistened filter papers in a seed germination incubator at 27±2°C with 90% relative humidity. Seeds are also to be kept for germination at 20, 25, 27, 30, 35°C and alternating temperatures of 20 and 30°C. The emergence of radicle is considered as a criteria for seed germination.
