Why must wheat seed be clean and true to its variety?

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A large red and yellow combine harvester cuts through a golden wheat field, leaving neat rows of harvested grain behind. — Cereal farming Combine harvesting wheat.

It is essential for wheat seed to be true to its variety and free from foreign seeds to ensure crop purity and prevent contamination by other cereal crops and weeds.1

Using clean, high-quality seed is critical because seeds harvested directly by a combine harvester are often unsuitable for planting without preliminary treatment. Modern cleaning methods, such as the use of oscillating sieves or revolving cylinders, are employed to remove impurities. Furthermore, seeds are frequently treated with fungicides to prevent the transmission of diseases, which helps ensure a healthy and productive crop.1