Interpreting a Seed Germination Test
A student tests a lot of 500 g of wheat seed. She places 4 replicates of 100 seeds each on moist filter paper at 20 °C. After 7 days she counts 82, 86, 79 and 85 normal seedlings; 6, 4, 8 and 5 abnormal seedlings; and the rest are dead/ungerminated. The label claims 95% germination. The seed lot is 8 months old and was stored in a cloth bag in a humid room. The student concludes the lot is 'fine because average germination is above 80%'.
1. Calculate the average normal germination percentage and judge whether the lot meets the label claim.
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Normal seedlings: (82 + 86 + 79 + 85) / 4 = 332 / 4 = 83%. Abnormal seedlings: (6 + 4 + 8 + 5) / 4 = 23 / 4 = 5.75%. Dead/ungerminated: 100 − 83 − 5.75 = about 11.25%. Only normal seedlings count toward germination; abnormal seedlings are not usable plants. The lot is therefore about 83% germination against a 95% label claim - a shortfall of about 12 percentage points. The student's statement that it is 'fine because above 80%' is wrong: the judgement should be against the label claim and the minimum standard for certified seed, not an arbitrary 80%. The lot fails the claim and should not be sold as 95% germination.
2. Explain why the storage conditions matter and what the student should do before deciding to sow this lot.
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Wheat seed stored in a cloth bag in a humid room is exposed to high moisture and fluctuating temperature, which accelerates deterioration: respiration and fungal growth reduce viability, and the 8-month storage period is enough to show decline. The 5.75% abnormal seedlings are a warning sign of seed deterioration, not just handling damage. Before sowing, the student should: (1) re-test a fresh, properly drawn sample to confirm the result; (2) check moisture content and visible mould/odour; and (3) if the lot is to be used, adjust the sowing rate upward to compensate for the lower germination (e.g. if the target is a certain plant population, increase seed rate by roughly 95/83 ≈ 1.15, i.e. about 15% more seed). The judgement is to treat the lot as marginal, not 'fine', and to verify before committing a field.
3. If the farmer must sow this lot, what is one additional risk beyond lower plant stand?
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Seed-borne disease and seedling vigour. Deteriorated seed stored humidly is more likely to carry fungi (e.g. moulds on the seed surface) and to produce weak seedlings that emerge unevenly and are more susceptible to soil-borne disease and stress. So even with a raised seed rate, the farmer should consider a seed treatment and expect a less uniform crop. The judgement is that low germination is not the only cost; poor vigour and disease risk also reduce the effective value of the lot.