Daylength Effect on Leaf Emergence and Phyllochron in Wheat and Barley
An understanding of the effect of environment on leaf emergence and development is necessary in order to model crop growth and development. This study was designed to determine the effect of controlled daylength on leaf emergence rate and phyllochron in winter wheat (Triticum aestivum L.) and spring barley (Hordeum vulgare L.). Two sets of experiments were conducted in growth chambers at a constant 15 °C. For the first set, 10 experiments were done at daylengths between 8 and 24 h on four wheat and four barley genotypes. The emergence of new leaves at a given daylength was a linear function of time for all genotypes and daylengths, the R2 being 0.94 or greater. However, the slopes differed among genotypes and daylengths. As daylength increased, the leaf emergence rate (leaves/day) increased and phyllochron (degree-days/leaf) decreased, both curvilinearly. The R2 for the curve fittings were 0.98 or greater for all genotypes. The phyllochron ranged among eight genotypes from 92.4 ± 4.5 degree-days at 8-h daylength to 64.5 ± 5.0 degree-days at 24-h daylength. The phyllochron of barley was more sensitive to daylength than was that of wheat. In the second set of experiments, the phyllochron for ‘Stephens’ wheat changed quickly when plants were transferred from either 8 to 18 or 18 to 8-h daylengths. The decrease of phyllochron as daylength increases may explain in part why the phyllochron of wheat and barley growing in natural environments varies with planting date.
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