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ARS Home » Pacific West Area » Maricopa, Arizona » U.S. Arid Land Agricultural Research Center » Plant Physiology and Genetics Research » Research » Publications at this Location » Publication #220755
Title: FIELD-BASED EVALUATION OF VERNALIZATION REQUIREMENT, PHOTOPERIOD RESPONSE AND EARLINESS PER SE IN BREAD WHEAT (TRITICUM AESTIVUM L.)

Author
item HERNDL, MARKUS - U OF HOHENHEIM, GERMANY
item White, Jeffrey
item HUNT, L - U OF GUELPH, CANADA
item GRAEFF, SIMONE - U OF HOHENHEIM, GERMANY
item CLAUPEIN, WILHELM - U OF HOHENHEIM, GERMANY

Submitted to: Field Crops Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/8/2007
Publication Date: 2/1/2008
Citation: Herndl, M., White, J.W., Hunt, L.A., Graeff, S., Claupein, W. 2008. Field-based evaluation of vernalization requirement, photoperiod response and earliness per se in bread wheat (triticum aestivum l.). Field Crops Research 105: 193-201.

Interpretive Summary: The time of heading or flowering in a wheat field strongly affects grain yield and quality. Wheat cultivars vary how temperature and length of day affect time of flowering, and also differ in their intrinsic tendency to flower early or late. Three cultivar traits, vernalization (cold) requirement, photoperiod (daylength) response and earliness per se (EPS) are often characterized in greenhouse or growth chambers. However, use of non-field conditions can reduce the reliability of predictions of flowering under field conditions. This research was undertaken to determine whether field experiments could replace studies in artificial environments. Twenty-six wheat cultivars were evaluated under field conditions using two natural photoperiod regimes (from different dates of transfer to the field) and vernalization pre-treatments. The responses of the cultivars were quantified based on time of flowering under the different treatments. To test whether the obtained indices were truly predictive, results were compared with cultivar parameters estimated from a computer-based model of a wheat. Comparisons with the model parameters showed that it is important to consider earliness per se in characterizing vernalization and photoperiod sensitivity. Allowing for variation in EPS in the calibration improved the relation between observed versus simulated data substantially: correlations for photoperiod responses increased from r² = .34 (p <.01), to .82 (p <.001), and for vernalization, from r² = .88 (p <.001), to .94 (p <.001). In comparisons of observed flowering dates vs. dates predicted by the model, using data from independent field experiments, the model showed excellent predictive power (r2 of .98, p <.001), confirming that combining planting dates and vernalization pre-treatments can permit reliable, quantitative characterization of vernalization requirement, photoperiod response and earliness per se of wheat cultivars. These results should permit much more effective characterization of wheat cultivars for the three traits and thus improve our ability to predict time of flowering under diverse conditions of wheat production. This information, in turn, can help farmers make better decisions concerning a numerous crop management activities as well as improve our ability to predict the medium to long-range impacts of processes such as global warming.

Technical 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 to determine whether field experiments could replace controlled environment evaluations. 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 (RRVGDD) and photoperiod (RRPGDD) were quantified using reciprocal of thermal time to flowering, whereas earliness per se was estimated by calculating thermal time from seedling emergence until end of ear emergence for fully vernalized and late planted material. An additional index based on final leaf numbers was also calculated to provide an alternate characterization of response to vernalization (RRVFLN). 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, RRVGDD was compared with the vernalization parameter P1V, for photoperiod (RRPGDD), with P1D, and for earliness per se, EPS was compared with the sum of the durations of the first three phases (P1, P2 and P3). Comparisons with the model input parameters showed that it is important to consider earliness per se in the calibration procedure of vernalization and photoperiod sensitivity. Allowing for variation in EPS in the calibration improved the relation between observed versus simulated data substantially: correlations of RRPGDD with P1D increased from r² = .34 (p <.01), to .82 (p <.001), and of RRVGDD with P1V, from r² = .88 (p <.001), to .94 (p <.001). In comparisons of observed vs. simulated ear emergence dates for independent field experiments, the estimated model coefficients resulted in an r2 of .98 (p <.001). Overall, the results indicated that combining planting dates and vernalization pre-treatments can permit reliable, quantitative characterization of vernalization requirement, photoperiod response and earliness per se of wheat cultivars.