Predicting broccoli development: II. Comparison and validation of thermal time models

Abstract

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 broccoli ( Brassica oleracea L. var. italica Plenck) cultivars (‘Fiesta’, ‘Greenbelt’ and ‘Marathon’) from emergence to harvest maturity (Model 1), from emergence to floral initiation (Model 2), and from floral initiation to harvest maturity (Model 3). Comparisons were also made between Model 1 and Model 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 from 1983 to 1984 sowings of three cultivars (‘Premium Crop’, ‘Selection 160’ and ‘Selection 165A’), it predicted harvest maturity well. Prediction of floral initiation using Model 2 is useful for timing cultural practices, frost and heat avoidance. Where timing of floral initiation was recorded, predictions of harvest maturity were most precise using Model 3, since the variation which occurred from emergence to floral initiation was removed. The good predictions for Model 4 suggests that it would best predict the chronological duration from emergence to harvest maturity.