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Effect of Temperature on the Heading Date of Wheat Cultivars under a Lengthening Photoperiod¹

An experiment was conducted to evaluate the effect of temperature on the number of days to heading of five vernalized winter and five spring commonly grown wheat (Triticum aestivum, L. em Thell.) cultivars under an increasing daylength. Controlled environment chambers were set at 15.5 C (day) and 7.2 C (night), and 21.0 C (day) and 12.7 C (night). Temperatures, cultivars, and the temperature x cultivar interaction were all highly significant tor both days and degree-hours to heading. Winter and spring cultivars had approximately the same range in values. All cultivars headed more rapidly at the higher temperatures. Within each growth habit, the cultivars maintained the same approximate ranking at both temperatures, but varied in their interaction with temperature. More degree-hours were used by all cultivars at the warmer temperature indicating that only part of the increased temperature was translated into accelerated heading. Each cultivar has a specific set of phenological control mechanisms which can affect the interaction with environment in final yield expession.

Key Words: Light Daylength • Winter wheat • Spring wheat • Phenology • Yield modeling • Ear development • Triticum aestivum L. em Thell • Latitude requirements • Heat units

² Professor, Institute of Horticulture, Univ. of Isfahan, Iran, and professor, Dep. of Agronomy, Colorado State Univ., Ft. Collins, CO 80523.

Received for publication May 31, 1979.