Prediction of rose shoot development: Model validation for the cultivar 'Cara Mia' and extension to the cultivars 'Royalty' and 'Sonia'

Temperature effects on the rate of rose shoot development were previously modeled using a thermal units (heat units) approach (Pasian and Lieth, 1994). To validate that model, developmental events were tracked over time for 'Cara Mia', 'Royalty', and 'Sonia' rose (Rosa hybrida) plants. These events, consisting of the occurrence of 'bud break', unfolding of each leaf, 'visible flower bud', or 'ready for harvest' were recorded daily throughout the experiment period for shoots of each cultivar. Hourly average air temperatures were monitored continuously and used to compute the accumulated thermal units (benchmarks) to each developmental stage. The shoot development model developed previously was found to be valid for predicting the stages of development of 'Cara Mia' flowering shoots. This model, however, required adjustments for successful use with 'Royalty' and 'Sonia'. Although the base temperatures used in the thermal units computation for 'Royalty' and 'Sonia' did not differ significantly from the one for 'Cara Mia', using cultivar-specific benchmarks resulted in significant prediction improvements. This indicates that benchmarks for each phenological stage need to be specific to each cultivar. The newly calculated benchmarks for the cultivars 'Royalty' and 'Sonia' require future validation. The model is suitable for timing of rose crops and deciding on temperature set-points.