JWSS - Journal of Water and Soil Science

Sensitivity of developmental stages of three sunflower cultivars to day length and temperature changes under field conditions were evaluated, and their development rates during various growth stages were modeled in a field experiment conducted in 1996 at the Agricultural Research Station, Isfahan University of Technology. Five dates of planting (April 27, May 12 and 27, and June 12 and 29) and three open pollinated sunflower cultivars (Record, Vnimik 8931 and Armavirec) were evaluated using a randomized complete block design with split-plot layout in three replications. Date of planting was considered to be the main plot and cultivars were randomized in sub-plots.

Number of days from planting (P) to head visible (HV) and P to first anther (FA) were significantly reduced with delay in planting as the result of increase in temperature during these periods. Number of days from P to physiological maturity (PM) was also significantly reduced with delay in P. This response, however, could not be explained by changes in temperature variables or day length. Number of days from HV to FA, in harmony with the partial stability of maximum and minimum temperatures during this period, was not affected by date of planting. Duration from FA to PM of the last planting date was significantly shorter than the other planting dates. This response was related to the persistence of the effect of high and stable maximum temperatures prevailing during HV to FA period of the last planting date. Armavirec was significantly earlier than Record and Vnimic 8931 for number of days from P to HV and from P to FA Cultivars showed significantly large differences for the FA to PM and P to PM durations. Armavirec was the earliest and Record was the latest cultivar. Based on the results obtained, it may be concluded that the cultivars under study were non-sensitive to photoperiod. Development rate (DR) of Armavirec responded linearly and DR of Record and Vnimic 8931 responded non-linearly to increases in temperature variables during P to HV and P to FA Development of Vnimic 8931 was faster than Record at high temperatures. DR of the cultivars decreased linearly during P to PM as day length increased. The relationship between DR and photoperiod could be used as a practical model for estimating P to PM duration of these sunflower cultivars.