Modeling phyllochron in wheat and barley

Graduation date: 1989An understanding of the effect of environment on\ud phyllochron (degree-days between two successive leaves) is\ud necessary to model cereal crop canopy growth. This study\ud was designed to investigate the relationships of phyllochron\ud to temperatures and daylengths in winter wheat (Triticum\ud aestivum L.) and spring barley (Hordeum vulgare L.). A\ud series of experiments at different temperatures and\ud daylengths were conducted in growth chambers on four winter\ud wheat and four spring barley genotypes, and in outdoor pots\ud and field plantings on two of the winter wheat genotypes.\ud In a given constant environment the leaves of a\ud particular wheat and barley genotype emerged at a constant\ud rate. However, the leaf emergence rate (leaves /day) and\ud phyllochron differed among temperatures, daylengths, and\ud genotypes. The leaf emergence rates increased non-linearly\ud with increasing temperature until an optimum temperature was\ud reached and then declined. The phyllochron increased\ud exponentially as temperature increased. As daylength\ud increased, the leaf emergence rate increased and phyllochron\ud decreased, both curvilinearly.\ud Different temperatures and daylengths appeared\ud interactive on leaf emergence rate and phyllochron in\ud controlled environments. These combined effects of\ud temperature and daylength on phyllochron could be quantified\ud as a linear relationship of phyllochron to the ratio of\ud daily degree-days to daylength hours (thermo/photo ratio).\ud In outdoor pots and in the field, the phyllochron was\ud constant throughout the period of development of a\ud particular planting of Stephens or Yamhill wheat, but varied\ud with planting date. The response of phyllochron to planting\ud date was correlated to the thermo/photo ratio during\ud seedling emergence. The results in this research suggest\ud that the linear algorithm between phyllochron and\ud thermo/photo ratio during seedling emergence can be used to\ud predict the phyllochron of both wheat and barley in\ud different planting environments. However, a specific\ud coefficient defining the linear regression intercept must be\ud determined for each cultivar