Response to Temperature in a Stand of Pearl Millet (Pennisetum typhoidesS. & H. )

Abstract

Stands of millet were grown in temperature-controlled glasshouses maintained at mean air temperatures of 19-31.degree. C and sub-plots were heated or cooled to examine the effect of soil temperature on early plant development. Soil temperature influenced all aspects of early vegetative development: the emergence of seedlings, the initiation, appearance and final number of leaves and tillers. Results are presented in terms of both chronological and thermal time (the summation of degree days (.degree. C d) above an extrapolated base (Tb) determined from the rate/temperature relation). Rates of the processes examined increased linearly with temperature, but the duration of vegetative phases appeared to be constant between 19-30.degree. C. The rate of all processes can therefore be described by specific thermal time (.theta.) e.g. 26.degree. C d for each leaf initiated and a base temperature (Tb) which was similar for all the vegetative processes examined, .theta. was relatively constant over the range of irradiance and saturation deficit experienced in the experiments. The results are compared to previous data for millet and other tropical species.