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

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Abstract
This paper examines the use of thermal time (accumulated temperature) to analyse the effects of temperature on the development of pearl millet. The plants were grown in columns of soil within stands of millet growing in controlled environment glasshouses. A range of almost constant soil temperatures was maintained at a number of air temperatures that were allowed to vary sinusoidally throughout the day. The number of root axes and lateral roots were counted on several occasions for young plants by destructive sampling of the columns. The results show that root axis and lateral development is related to the thermal time measured at the shoot meristem using a base temperature of 12 ° C. The shoot meristem temperature consistently proved to be more closely related to root development than soil temperature at a depth of 5.0 cm. The difficulty of relating root development to temperature at a particular depth is discussed, together with the problems of selecting an appropriate base temperature. For the concept of thermal time to provide a clearer understanding of temperature effects on root development, it will be necessary to take account of possible differences in the thermal response of different parts of the root system and of other environmental factors, particularly soil water status.