title: Simulating the influence of vernalization, photoperiod and optimum temperature on wheat developmental rates.
abstract: OBJECTIVE
  Accurately representing development is essential for applying crop simulations to investigate the effects of climate, genotypes or crop management. Development in wheat (Triticum aestivum, T. durum) is primarily driven by temperature, but affected by vernalization and photoperiod, and is often simulated by reducing thermal-time accumulation using vernalization or photoperiod factors or limiting accumulation when a lower optimum temperature (T(optl)) is exceeded. In this study T(optl) and methods for representing effects of vernalization and photoperiod on anthesis were examined using a range of planting dates and genotypes.
  
  
  METHODS
  An examination was made of T(optl) values of 15, 20, 25 and 50 degrees C, and either the most limiting or the multiplicative value of the vernalization and photoperiod development rate factors for simulating anthesis. Field data were from replicated trials at Ludhiana, Punjab, India with July through to December planting dates and seven cultivars varying in vernalization response.
  
  
  RESULTS
  Simulations of anthesis were similar for T(optl) values of 20, 25 and 50 degrees C, but a T(optl) of 15 degrees C resulted in a consistent bias towards predicting anthesis late for early planting dates. Results for T(optl) above 15 degrees C may have occurred because mean temperatures rarely exceeded 20 degrees C before anthesis for many planting dates. For cultivars having a strong vernalization response, anthesis was more accurately simulated when vernalization and photoperiod factors were multiplied rather than using the most limiting of the two factors.
  
  
  CONCLUSIONS
  Setting T(optl) to a high value (30 degrees C) and multiplying the vernalization and photoperiod factors resulted in accurately simulating anthesis for a wide range of planting dates and genotypes. However, for environments where average temperatures exceed 20 degrees C for much of the pre-anthesis period, a lower T(optl) (23 degrees C) might be appropriate. These results highlight the value of testing a model over a wide range of environments.
authors.affiliation: USDA-ARS, Agricultural Systems Research, 2150 Centre Avenue, Building D, Suite 200, Fort Collins, CO 80526, USA. Greg.McMaster@ars.usda.gov
authors.forename: Gregory S
authors.initials: GS
authors.lastname: McMaster
authors.forename: Jeffrey W
authors.initials: JW
authors.lastname: White
authors.forename: L A
authors.initials: LA
authors.lastname: Hunt
authors.forename: P D
authors.initials: PD
authors.lastname: Jamieson
authors.forename: S S
authors.initials: SS
authors.lastname: Dhillon
authors.forename: J I
authors.initials: JI
authors.lastname: Ortiz-Monasterio
mesh_terms: D018556:Crops, Agricultural / Q000254:growth & development; D005838:Genotype; D007194:India; D008954:Models, Biological; D017440:Photoperiod; D012621:Seasons; D013696:Temperature; D013997:Time Factors; D014908:Triticum / Q000254:growth & development*