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The Growing Point of Fall-Sown Wheat: A Useful Measure of Physiologic Development¹

Breeders developing winter wheat (Triticum aestivum L. em Thell) cultivars intended for early seeding need to be able to identify for discard lines which are likely to complete early developmental stages too rapidly in the fall, with consequent increased vulnerability to winterkill or spring frost injury. A refined scale of head development of wheat has been devised and is illustrated, consisting of 12 stages. This scale has been used to classify precisely the head development of more than 300 cultivars and advanced lines of wheat. To illustrate the application of the scale, 15 cultivars grown at Central Ferry in 1976 were classified. On 30 November, two spring and one facultative cultivars were identified as vulnerable to winterkill. By 4 April, the 14 surviving cultivars had reached head stages vulnerable to frost. Of these, four cultivars had culms short enough that the heads were retained below the soil surface and protected from frost while the remaining 10 were without that protection. By employing the scale, plus measurement of stem elongation during early spring, wheat germplasm that is potentially vulnerable to winterkill or frost injury can be identified and discarded.

Key Words: Phenology • Head development • Floral initation

² Research agronomist, USDA, Pullman, WA 99164.