Predicting broccoli development - II. Comparison and validation of thermaltime models

Models predicting broccoli ontogeny and maturity should ideally be precise and readily adopted by farmers and researchers. The objective of this study was to compare the predictive accuracy of thermal time models for three br occoli (Brassica oleracea L. var. italica Plenck) cultivars ('Fiesta', 'Gre enbelt' and 'Marathon') from emergence to harvest maturity (Model 1), from emergence to floral initiation (Model 2), and from floral initiation to har vest maturity (Model 3). Comparisons were also made between Model 1 and Mod el 4 (Models 2 and 3 combined). Model 1 is useful when the timing of floral initiation is not known. When Model 1 was tested using independent data fr om 1983 to 1984 sowings of three cultivars ('Premium Crop', 'Selection 160' and 'Selection 165A'), it predicted harvest maturity well. Prediction of f loral initiation using Model 2 is useful for timing cultural practices, fro st and heat avoidance. Where timing of floral initiation was recorded, pred ictions of harvest maturity were most precise using Model 3, since the vari ation which occurred from emergence to floral initiation was removed. The g ood predictions for Model 4 suggests that it would best predict the chronol ogical duration from emergence to harvest maturity. (C) 2000 Published by E lsevier Science B.V.