Field-based evaluation of vernalization requirement, photoperiod response and earliness per se in bread wheat ( Triticum aestivum L.)

Abstract

Vernalization requirement, photoperiod response and earliness per se (EPS) of bread wheat cultivars are often determined using controlled environments. However, use of non-field conditions may reduce the applicability of results for predicting field performance as well as increase the cost of evaluations. This research was undertaken, therefore, to determine whether field experiments could replace controlled environment studies and provide accurate characterization of these three traits among winter wheat cultivars. Twenty-six cultivars were evaluated under field conditions using two natural photoperiod regimes (from different transplanting dates) and vernalization pre-treatments. Relative responses to vernalization (RRV GDD) and photoperiod (RRP GDD) were quantified using the reciprocal of thermal time to end of ear emergence, whereas earliness per se was estimated by calculating thermal time from seedling emergence until end of ear emergence for fully vernalized and lately planted material. An additional index based on final leaf numbers was also calculated to characterize response to vernalization (RRV FLN). To test whether the obtained indices have predictive power, results were compared with cultivar parameters estimated for the CSM-Cropsim-CERES-Wheat model Version 4.0.2.0. For vernalization requirement, RRV GDD was compared with the vernalization parameter P1V, for photoperiod (RRP GDD), with P1D, and for earliness per se, EPS was compared with the sum of the component phase durations. Allowing for variation in EPS in the calibration improved the relation between observed versus simulated data substantially: correlations of RRP GDD with P1D increased from r 2 = .34 ( p < .01), to .82 ( p < .001), and of RRV GDD with P1V, from r 2 = .88 ( p < .001), to .94 ( p < .001). In comparisons of observed versus simulated anthesis dates for independent field experiments, the estimated model coefficients resulted in an r 2 of .98 ( p < .001) and root mean square error of 1 d. Overall, the results indicated that combining planting dates with vernalization pre-treatments can permit reliable, quantitative characterization of vernalization requirement, photoperiod response and EPS of wheat cultivars. Furthermore, emphasize the need for further study to clarify aspects that determine EPS, including whether measured EPS varies with temperature or other factors.