Temperature Effect on Leaf Emergence and Phyllochron in Wheat and Barley

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Abstract
An understanding of the effect of environment on leaf emergence is necessary for modeling crop canopy growth. This study was to determine the effect of controlled temperature on leaf emergence rate and phyllochron in four winter wheat (Triticum aestivum L.) and four spring barley (Hordeum vulgare L.) genotypes. Nine experiments were conducted in growth chambers at constant temperatures between 7.5 to 25 °C. The number of leaves per culm was recorded daily from seedling emergence until the fourth leaf was mature. At a given temperature, the emergence of new leaves was a linear function of time for all genotypes, with R2 values not less than 0.95. The slopes of the linear regressions, which are the leaf emergence rates (leaves/day), however, differed among genotypes and among temperatures within genotypes. For all genotypes, the leaf emergence rates increased parabolically with increasing temperature until an optimum temperature was reached and then declined. These responses could be described with quadratic polynomials with R2 values greater than 0.96 for all genotypes. As temperature increased, the phyllochron (degree‐days/leaf) increased exponentially. The relationships between phyllochron and temperature fit exponential equations with R2 0.97 or greater for all genotypes. The phyllochron ranged among the eight genotypes from 57.2 ± 5.2 degree‐days at 7.5 °C to 116.2 ± 7.1 degree‐days at 25 °C. These results suggest that the temperature effect must be considered in modeling phyllochron in wheat and barley.