Physiological and Numerical Components of Wheat Yield

Wheat ( Triticum aestivum L.) grain yields have increased substantially since the 1950s ( Slafer, Satorre, and Andrade, 1993 ; Simmons, 1987 ; Schmidt, 1984 ). About half of this yield improvement has resulted from genetic increases in grain yield and the other half is due to improved production technologies and practices. Genetic improvement in wheat yield can be attributed to selection for improved agronomic characteristics conferring either higher yield potential or greater stress tolerance ( Slafer, Satorre, and Andrade, 1993 ; Simmons, 1987 ; Schmidt, 1984 ). The exact physiological basis for the genetic gain in grain yield potential is unknown. However, it stands to reason that the physiological processes controlling wheat yield have been altered during the course of yield improvement, and that new cultural practices have changed how these processes affect wheat growth and development.