determination of duration of developmental stages of sofea safflower cultivar by temperature and day length

agricultural practices always need accurate information about occurrence of particular developmental stages. data from planting dates trials conducted over the kabotar-abad agricultural research station, isfahan during 2003-2009 were used to develop models for estimating developmental stages duration of sofea safflower variety. to model duration of each developmental stage, duration of each developmental stage considered as the dependent variable and various temperature variables, day length and combination of them considered as the independent variables in a stepwise regression procedure. a step of regression was considered appropriate when the highest r2 was accompanied by the significant (p≤ 0.05) regression coefficient and partial r2. the number of days from planting to emergence, emergence to head visible, emergence to flowering, emergence to ripening and flowering to ripening were affected by planting dates. developmental stages duration reduced as temperature increased. day length had the highest effect on emergence to head visible and emergence to flowering durations and reduced as day length increased. tmin, t2min and t4min were the variables which entered the regression model and explained about 91% of variation of planting to emergence duration. durations of emergence to head visible and emergence to flowering were explained by dl×tmax and dl2×t2max in accuracy of 90% and 96%, respectively. t3max and t4max explained the most variance (99.64%) of emergence to ripening duration. t2min was the only variable which entered the regression model and explained about 63% of variation of flowering to ripening duration. the results of this study showed that the contribution of temperature and day length is not constant in different developmental stages of safflower.