Prediction of Development of Asiatic Lilies Based on Air Temperature and Thermal Units

Abstract

`Butter Pixie' and `Horizon' Asiatic lilies (Lilium spp.), were grown at several temperatures. The phenological events of visible shoot (VS), visible flower bud (VB), and open flower (OF) were recorded daily. Based on these events, phenophases from VS to VB (VS:VB), from VB to OF (VB:OF), and from VS to OF (VS:OF) were defined. Daily rates of development to complete a phenophase increased with temperature. Nonlinearity was obvious for all phenophases around 25 °C for `Horizon' and 27 °C for `Butter Pixie'. A piece-wise linear regression change point model was fitted to each dataset. The base temperature (Tb), the temperature at which the nonlinearity occurred (Ti), and the temperature for fastest development (To) could then be determined. Tb for the phenophase VS: OF was -0.4 °C for `Butter Pixie' and 3.0 °C for `Horizon'. Ti for `Butter Pixie' was 25.7 °C for VB:OF and 26.1 °C for the phenophase VS:OF. However, Ti for `Horizon' was found only for the phenophase VS:OF. To complete the phenophase VS:OF, 1102.2 degree days (°Cd) were predicted necessary for `Butter Pixie' and 833.2 °Cd for `Horizon'. Predicted time of events was compared with observed values. Subdividing VS:OF into VS:VB and VB:OF and using their respective Tb and TU reduced the average prediction error from 2.13 to 1.87 d for `Butter Pixie' and from 2.39 to 1.86 days for `Horizon'.