Farm-saved wheat seed with low germination and loose smut
A farmer has 2 ha for wheat. He has 180 kg of farm-saved seed of a tall, late-sown local variety with a germination test of 70% and 5% inert matter; the seed lot also shows 2% loose smut infection. The recommended seed rate for timely sown wheat is 100 kg/ha with 90% germination. He can buy certified seed of a rust-resistant, 120-day variety at ₹45/kg, or use his seed and save money. Sowing is delayed by 15 days. The previous crop was rice, and the field has a history of loose smut. His budget allows either certified seed for 2 ha or farm seed plus one fungicide treatment.
1. Calculate the adjusted seed rate for the farm-saved seed and decide whether it can cover 2 ha. What are the implications?
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Adjustment for germination and inert matter: adjusted rate = 100 kg/ha × (90/70) × (100/(100-5)) = 100 × 1.286 × 1.053 = about 135 kg/ha. For 2 ha, he needs about 271 kg. He has only 180 kg, which covers 180/135 = 1.33 ha.
Late sowing: a 15-day delay should increase the seed rate by roughly 10-20% to compensate for reduced tillering. Using 120 kg/ha as the base, the adjusted rate becomes 120 × 1.286 × 1.053 = about 162 kg/ha, and 2 ha would need 324 kg. His stock covers only about 1.1 ha.
Implication: he cannot sow 2 ha with the farm-saved seed alone. Using it at the calculated rate on part of the field and buying certified seed for the rest is feasible, but the varieties would differ in maturity and height, complicating harvest and irrigation. The certified variety is rust-resistant and 120 days, better suited to late sowing than the tall local type. If the budget allows only one choice, buy certified seed for all 2 ha; the farm seed is insufficient, low-germination and smut-infected. If he must economise, buy certified seed for 1 ha and treat the farm seed for the remaining 0.9-1 ha, but do not sow untreated farm seed.
2. Explain the loose smut risk and the seed-treatment decision for the farm-saved seed.
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Loose smut of wheat is caused by Ustilago segetum var. tritici and is internally seed-borne. Infected seed looks normal, but the fungus grows with the seedling and produces smutted ears at flowering; spores then spread to healthy ears. A 2% infection can cause at least 2% direct loss and further secondary spread, especially with rice-wheat residue and delayed sowing. No field spray after flowering can cure it.
Certified seed is tested and treated, so it avoids this risk. For the farm-saved lot:
- Chemical treatment: carboxin at 2 g/kg seed, tebuconazole at 1.5 g/kg, or carbendazim at 2 g/kg. Use a slurry or rotary seed dresser for even coverage.
- Hot-water treatment: 52°C for 10 minutes, then cool and dry. This kills the internal mycelium but may reduce the already low 70% germination, so test a sample afterwards.
- Solar treatment is less reliable and not a substitute for certified seed.
Because germination is only 70% and 2% of seed is infected, treatment may not fully eliminate the pathogen. Treat the seed, re-test germination, and discard the lot if germination falls below 60%. In the field, rogue and burn smutted ears before spores spread. The safer decision is to use the farm seed for grain or feed, not for seed, and buy certified seed for sowing.