Modeling flowering response to temperature and photoperiod in safflower

Abstract

Accurate prediction of flowering is an essential step in understanding the plants’ growth and yield. For this purpose, a field experiment was conducted with 12 sowing dates (across 2012 and 2013) on four cultivars of safflower (Esfahan, Goldasht, Sofeh, and Padideh). Six combinations of functions including three temperature-related and two photoperiod-related functions were compared in a development rate model (multiplicative model). Amongst the composite functions examined using the multiplicative model, functions of the segmented-segmented (SS) for Esfahan, Goldasht and Sofeh and beta-segmented (BS) for Padideh were appropriate. The base and optimum temperatures were estimated 2.6-4.3 and 29-29.6 °C for Esfahan, Goldasht and Sofeh, while they were 0 and 22.4 °C for Padideh, respectively. The ceiling temperature was fixed at 40 °C for all cultivars. Estimation of critical photoperiod (Pc) ranged from 13.2 to 13.5 h in all cultivars. Photoperiod sensitivity coefficient (Ps) was estimated between 0.169 and 0.448 h.d-1 for all cultivars. Sensitivity to photoperiod was different among the cultivars and Padideh was more sensitive to photoperiod than other cultivars. The results showed that the cultivars required 53.0 to 79.0 biological days from emergence to flowering. The evaluation of development rate model also showed that the model well predicted days to flowering (r = 0.94, RMSD = 5.5 days and CV = 7.5%). Therefore, this model can be incorporated into the simulation model of growth and yield of safflower.