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Effects of Air Temperature and Water Stress on Apex Development in Spring Wheat¹

Grain yield of hard red spring wheat (HRSW) (Triticum aestivum L.) is influenced by the number of spikelets produced per spike. There is a need to better understand, for predictive purposes, the effects of water and temperature on apex differentiation, spike and spikelet development, and number of spikelets. The effects of these two factors on apex development and number of spikelets produced per spike were studied in a controlled environment using ‘Sinton’ HRSW. Data on spikelets per spike from field studies conducted at Mandan, ND were included to evaluate temperature effects during the spikelet development phase on number of spikelets formed per spike. Plants grown at 18°C for 4, 8, or 12 days from emergence, and thereafter at 26°C required less time to reach double ridge and terminal spikelet development stage, had a shorter spikelet development period, and produced fewer spikelets per spike than plants grown initially at 26°C for 4, 8, and 12 days and thereafter at 18°C. These data indicated that higher air temperature (26°) from about 6 to 8 days prior to apex double ridge through terminal spikelet formation reduced the number of spikelets per spike. Plants exposed to water stress starting 12 days after seedling emergence required the same duration to develop double ridges as the controls, but stressed plants had a shorter spikelet development stage, resulting in fewer spikelets per spike. The data suggested that the transition of the apex from vegetative to reproductive growth is a continuum. Regression analysis of spikelets per spike at the apex terminal spikelet stage on maximum daily air temperature during the spikelet formation period showed a significant negative linear relationship (R² = –0.69). This relationship, along with application of growing-degree days for estimating the spikelet development period, has application for enhancing prediction of grain yields from number of spikelets produced per spike.

Key Words: Triticum aestivum L. • Wheat ear • Wheat spike • Floral initiation • Crop modelling • Spikelets

² Plant physiologist and soil scientists, respectively, USDA-ARS, Northern Great Plains Res. Lab., P.O. Box 459, Mandan, ND 58554.

Received for publication March 10, 1986.