Estimation of phenological parameters in SSM-Wheat model for bread wheat (Triticum aestivum L.) genotypes in Golestan province of Iran

To estimate required parameters of phenology sub-model in SSM-Wheat model (cardinal temperatures, critical photoperiods and photoperiod sensitivity coefficient) and to determine of the biological day for eight bread wheat genotypes (Morvarid, Tajan, Kohdasht, Darya, Gonbad, Arta, N-87-20 and N-87-19) in Golestan province of Iran in 12 sowing dates, an experiment was carried out using randomized complete block design with four replications during 2012 and 2013 cropping cycles. Beta-quadratic model was used to explain the relation of stem elongation rate of the wheat genotypes in response to temperature and photoperiod. The bread wheat genotypes did not have significant differences in critical photoperiod and cardinal temperature. However, they were significantly differ for biological day and photoperiod sensitive coefficient. Therefore, cardinal temperatures including; base, optimum and ceiling temperatures were used in 0, 28 and 40 °C, respectively, for all of genotypes in the model. In addition, the critical photoperiod fixed on 21 hours in this model. Coefficient of sensitivity to photoperiod varied from0.00272 to 0.0091 for genotypes. The bread wheat genotypes did not show significant differences in terms of biological days (bd) in phenological stages including; sowing to emergence (6.2 bd), tillering to stem elongation (7.9 bd), booting to heading (3.4 bd), heading to anthesis (6.4 bd) and physiological maturity to harvest maturity (6.8 bd). However, significant differences observed in phenological stages emergence to tillering (6.5-8.8 bd), stem elongation to booting (4.7-5.9 bd) and anthesis to physiological maturity (21.1-24.8 bd) among genotypes. Model evaluation indicated that root mean square error for biological days to anthesis and days to physiological maturity was 7.7 (with coefficient of variation 10.3%) and 1.7 (with coefficient of variation 2.5%), respectively. Therefore, parameters of cardinal temperatures, critical photoperiods, photoperiod sensitivity coefficient and biological day were estimated reasonably for bread wheat genotypes of Golestan province.