Thermal time has been used to represent the effect of the air temperature on plants growth and development. Thermal time is a simple method and a better time descriptor than calendar days in plants. The objective of this study was to calculate the thermal time by different calculation methods for different developmental phases (emergency to tuber initiation, from tuber initiation to beginning of senescence and from beginning of senescence to harvest time) in field grown potato cultivar Asterix. Field experiments were carried out at Santa Maria RS, Brazil, with eleven planting dates during 2003 and 2004. The experimental design was a complete randomized block design with four replications. Thermal time for different developmental phases varied according to planting date, calculation method, and cardinal temperatures. These results indicate that the thermal time should be used with caution to tell time in potato.
thermal sum; cardinal temperatures; plant development
