THE PHYLLOCHRON - WHERE DO WE GO IN THE FUTURE

This paper integrates, expands, and applies information from seven articles written for a symposium on the use of phyllochron concepts for describing shoot development in grasses. Generally, no one environmental factor is a perfect predictor of plant development rate. Factors that influence development rate include genetics, nutrition, water supply, day length, light, and temperature. Average air temperature, when accumulated in the form of a degree-day sum, does at times correlate linearly with plant developmental descriptors such as the Haun stage. The interval between visual appearance of successive leaves (the phyllochron) may be approximated as a constant number of degree-days for such a situation. If not only the visual extension of plant organs but the initiation of both vegetative and reproductive organs at active growing points can be linearly correlated with average temperature sums, an elegantly simple line diagram illustrates the full season synchronous initiation and development of all plant vegetative and reproductive parts. Development of each organ at the cellular level may be represented. This simple but complete representation of synchronous development based on the phyllochron provides a foundation for describing and improving understanding of the genetic and environmental control of grass development rate.