Temperature Effects Prior to Double Ridge on Apex Development and Phyllochron in Spring Barley

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Abstract
Number of spikelets is a major component of grain yield in spring barley (Hordeum vulgare L.). Since air temperature strongly affects spike components in spring seeded cereals, the large variations in daily temperature or delays in planting dates, common to spring barley growing areas in the Northern Great Plains, make it important to understand temperature effects on spike and whole plant development for managemenat nd modeling purposes. The objectives of this study were to determine effects of changing temperature regimes on the phyllochron, apex development, and spike components in spring barley. ‘Bowman’ (two‐rowed) and ‘Azure’ (six‐rowed) were grown in controlled environment chambers and at constant temperatures of 18 and 26°C and at either 18 or 26°C for 4, 8, and 12 d after emergence and then transferred to the other temperature. Phyllochron was greater for control plants at 26 than at 18&C and for plants first grown at 18 then at 26&C compared with those grown at 26 then at 18&C. Apex double ridge stage occurred between 8 and 12 d after seedling emergence. Temperature following apex double ridge stage had a greater affect on duration of spikelet formation stage than temperatures prior to double ridge. Spikelets, kernels, and heads per plant were generally fewer for plants first grown at 18 then at 26°C compared with plants first grown at 26°C then at 18°C. These data suggest that temperature during the critical spikelet development phase had the greatest effect on spike components. Spike development coincided more with plant Haun than accumulated growing degree‐days (GDD), whereas the phyllochron responded oppositely. Thus, knowing when the apex forms spikelets is necessary for interpretation of plant responses, making management decisions, and model development.

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