Effects of temperature and day length on development rate of safflower cultivars

Abstract

Cropdevelopment is qualitative changes planned that makes the plant to ripening. Under irrigated conditionsexpected only climate elements able to change of plant growth and developmentand under these conditions, temperature and day length have more effective thanthe other elements. Data from planting dates trials conducted over theKabootar-Abad Agricultural Research Station during 2003-2009 were used todevelop models for estimating development rate of three varieties, Arak, ZendehRud and Goldasht. To calculate of developmental rate of every stage, durationof every stage was inversed. For determining model of development rate of everystage, development rate considered as dependent variable and day length,thermal variables and combination of these considered as independent variablesin step wise regression. A step of regression was considered appropriate if thehighest R2 was accompanied by the significant (p≤0.05) regressioncoefficient. Evaluation of model accuracy and sensitivity was performed, usingthe data of 2008-2009 that there was not any role in forming of models. No. of  days from planting to emergence,emergence to heading, emergence to flowering, emergence to ripening andflowering to ripening were affected by planting dates. By increasingtemperature, developmental stage periods decreased. Day length had the mosteffect on emergence to heading and emergence to flowering period and byincreasing it, decreased. Tmean was the only variablethat entered to model and explained about 76% of development rate of emergenceperiod. About 83% of development rate of emergence to heading stage wasdetermined by Tmax×DL. T2max×DL2 explainedabout 92% of development rate of emergence to flowering stage. T2max×DL2 with T4maxexplained about 81% variations of developmental rate of emergence to ripeningstage. T3max was the only variable that entered the model ofdevelopment rate of flowering to ripening stage and expressed about 47%variations of it. Contribution of thermal and day length parameters indetermining of rate of different developmental stages is not constant. This maybe related to different physiological nature of developmental stages anddifferences reactions of these stages to climatologic, edaphic and agronomicelements and interaction among them and with genotype of plant.  Contribution of thermal and day lengthparameters in determining of rate of different developmental stages is notconstant.