J. Steininger
C. C. Pasian
Temperature affects the rate of development of Lilium (Asiatic hybrid). The long-term objective is to evaluate thermal units as a tool for crop timing. The objective of this work was to determine Lilium base temperature (Tb). A total of 218 plants of two cultivars, 'Butter Pixie' and 'Horizon,' were used. Phenological observations were made on plants during eight plantings over a two-year period. Developmental stages observed were shoot visible out of the soil (SV), flower bud visible (BV), and open flower (OF). The two cultivars were grown in four different greenhouse compartments with settings at 13, 18, 24, and 27 degrees C respectively.
During periods of extreme outdoor temperatures, actual temperature deviated from the settings. Actual temperatures were constantly monitored with copper-constantan thermocouples and stored in a datalogger. Rates of development were calculated as the inverse of the numbers of days to complete a given phenological phase. Tb values were obtained by calculating the x-interception of the linear regression describing rate of development as a function of mean air temperatures.
Tb for 'Butter Pixie' and 'Horizon' for the entire growth cycle (SV through FO) were -0.44 degrees C and 0.48 degrees C respectively. The production cycle can be divided into two phases: SV - BV and BV - FO. For 'Horizon,' Tb for these phases were -0.78 and 0.83 degrees C respectively. For 'Butter Pixie,' these Tb were 1.99 and -0.8 respectively.
More observations of development at mean temperatures higher than 35 degrees C and lower than 13 degrees C will be attempted in the future in order to determine the temperature at which maximum rate of development occurs.