DEMO Practical Seed Viability and Moisture Content 26OCT2026
This video records the practical session in which we ran two experiments in a single day. The first tests whether seeds are alive, using the tetrazolium test and the paper towel germination test. The second measures how much water the seeds hold, using rapid oven drying and slow sun drying. Two seed types were used: maize (Zea mays), an endospermous (albuminous) seed, and bean (Vigna unguiculata), a non-endospermous (exalbuminous) seed.
Watch the video: https://youtu.be/Lgxq9Pk0Z-A
The practical manual is here: AGR3301 Crop Physiology Practical: Seed Viability, Germination and Moisture Content. It now combines the viability, germination and moisture content practicals into one manual, in the same order as the demonstration.
English subtitles are available on the video. Short notes in square brackets clarify a few points where what was said in class needs correcting or where the class procedure differs from the manual.
1. Tetrazolium (TZ) test: a quick check for living tissue
The tetrazolium test uses a colourless salt, 2,3,5-triphenyl tetrazolium chloride (TTC). Living cells respire, and their dehydrogenase enzymes release hydrogen during respiration. TTC picks up this hydrogen and is reduced to triphenylformazan, which is red. Red tissue therefore means respiring, living tissue. Dead tissue stays unstained. The solution is light-sensitive, so the bottle is wrapped in aluminium foil.
The steps shown in the video:
Soak the seeds in water overnight. This softens them for cutting and lets the solution get into the tissues.
Cut each seed lengthwise, from top to bottom, through the middle of the embryo axis, so the embryo is exposed. Cutting from side to side misses the embryo.
Place the seeds in a Petri dish with the cut surface facing down, and pour in enough tetrazolium solution to submerge them fully.
Incubate at 35 °C for about 70 minutes (1 hour 10 minutes).
Score the staining. The red colour that counts is in the embryo, not in the endosperm or seed coat. In maize, the scutellum, coleorhiza, radicle and plumule should all stain red for the seed to be scored as viable.
Why 35 °C and not 40 or 50 °C? The staining depends on an enzyme reaction. Too much heat denatures the proteins, including the enzymes, so they can no longer carry out the reaction.
You will notice the maize seeds are pink-red rather than yellow. This seed was treated with thiram, a fungicide, and treated seed is dyed so that it is easy to recognise. Wear gloves, or wash your hands well after handling it, and do not rub your eyes.
The TZ test is quick, but it is destructive: once the seed is cut, it cannot grow. That is why we also run a germination test.
2. Germination test: the paper towel method (the popiah way)
The germination test shows whether seeds actually produce seedlings. It takes a week, but it is the direct answer to the question "will this seed grow?"
Use dry seeds, not the soaked ones.
Wash your hands with soap first. Dirty hands transfer fungal spores to the tissue, and after a week you get rotting seeds instead of seedlings. This matters more for the bean, which has no fungicide treatment.
Place a maximum of five seeds on moist tissue paper and roll it up the popiah way. Roll loosely, but after each turn press firmly between the seeds, so that each seed sits in its own pocket of wet tissue.
Prepare three rolls per seed type: three rolls of five seeds gives fifteen seeds per seed type, as three replications.
Spray the rolls to moisten them, not to drown them.
Put the rolls in a sealed plastic bag, labelled with your name using tape or a marker. At home, keep the rolls lying flat and side by side, not stacked on top of each other.
Use clean water. Water from a bottle you have been drinking from carries microbes from your mouth.
Check for contamination during the week, and repeat the test if the rolls become mouldy.
In the laboratory, the rolls can instead be kept in a tray covered with cling film. For this class, the rolls went into bags so students could take them home and monitor them.
After seven days, count the seeds that have produced a normal seedling with an intact root and shoot. Do not count mouldy seeds or diseased seedlings. Germination percentage is calculated as the number of germinated seeds divided by the total number of seeds, multiplied by 100. With five seeds per roll, each seed is worth 20%. For example, if 4 out of 5 seeds germinate in one roll, germination is 4 ÷ 5 × 100 = 80%. Over all fifteen seeds, if 13 germinate, germination is 13 ÷ 15 × 100 = 86.7%.
3. Seed moisture content: rapid drying and slow drying
Seed moisture content affects how long seeds survive in storage. Moist seeds respire more, heat up and invite fungal attack. Here we dried the same two seed types in two ways and compared the results.
Rapid drying. Take five dry, uncut seeds of each type and weigh each seed (fresh weight). Number or label every seed so you can match its fresh weight to its dry weight later. A pen mark or a small piece of tape works; this part is up to you. Dry the seeds in a glass Petri dish in the oven at 130 °C for 1 hour, then weigh each seed again (dry weight). One point to note: in the video I said 150 at first. The correct temperature is 130 °C, as said later in the session and as written in the manual.
Slow drying. Weigh each seed fresh, label it (for example, 1 for maize and 1B for bean), wrap it in dry tissue and put it in your group's labelled plastic bag. Poke several small holes in the bag first, so that moisture can escape; a sealed bag traps the water and the seeds will not dry. The seeds are dried in the sun for a week, and you then come back to weigh them again for the dry weight.
Moisture content is calculated on a fresh weight (wet) basis:
Moisture content (%) = (fresh weight − dry weight) ÷ fresh weight × 100
Worked example: a seed weighs 5.00 g fresh and 4.45 g after drying. The water lost is 5.00 − 4.45 = 0.55 g. Divide by the fresh weight: 0.55 ÷ 5.00 = 0.11. Multiply by 100: 0.11 × 100 = 11%. Remember to divide by the fresh weight before multiplying by 100.
Seed-testing laboratories that follow the International Seed Testing Association (ISTA) rules grind large seeds before oven drying and dry maize for longer than one hour. Our one-hour run with whole seeds is a quicker class version, so keep this in mind when you discuss your results.
4. Safety and good practice
Be careful with the blades, and do not play around while cutting.
Handle fungicide-treated seed with gloves, or wash your hands afterwards.
Do not eat during the practical.
Do not worry if the oven runs about 10 minutes longer than planned. Opening the door many times drops the temperature, and the oven takes time to recover.
5. Your lab report
Record your data in the tables in the manual and plot the graphs as shown there. Use the sample lab reports linked on the manual page as a guide to the expected format.
Video Transcript:
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