JWSS - Journal of Water and Soil Science

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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.

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A field experiment was conducted in 2000 at the Agricultural Research Station, Isfahan University of Technology, to model the response of four safflower genotypes to day length and temperature changes under field conditions. Five planting dates (March 12, April 12, May 10, June 8, and July 12) and four safflower genotypes (Arak 2811, local variety Koseh, Nebraska 10 and Varamin 295) were evaluated using a randomized complete block design with split-plot layout in three replications. Date of planting was considered as the main plot and cultivars were randomized in the sub-plots. Number of days from planting (P) to emergence (E), stem elongation (SE) to head visible (HV), and HV to flowering initiation (FI) significantly reduced with delay in planting as the result of increase in temperature during these periods. Number of days from P to SE, duration of flowering (DF) and termination of flowering (TF) to physiological maturity (PM) were significantly affected by planting date and reduced as day length increased. The same was observed in the case of number of days from P to 50% flowering (MF) and to PM. Large co-variation of day length with temperature may explain a portion of day length contribution to the variation in the above periods. Varamin 295 was later than other genotypes with respect to the duration from P to HV, and specially, for rosette duration. In addition and for unknown reasons, the rate of development (RD) of Varamin 295 at all developmental periods could not be explained by day length and/or temperature variables. Among other genotypes, Koseh with 125 days, and Nebrska 10 with 118 days from P to PM were the latest and the earliest genotypes, respectively. The response of Koseh to planting dates, as measured by the duration of various developmental stages, differed from Arak 2811 and Nebraska 10. This was attributed to the probable response of Koseh to day length. RD of Koseh, Arak 2811, and Nebraska 10 during P to MF was explained by a linear regression and RD of Koseh during P to PM by a polynomial regression with day length by mean temperature as an independent variable. RD of Arak 2811 and Nebraska 10 during P to PM was explained by minimum temperature. It seems that partial sensitivity of Koseh to day length has a considerable significance in its adaptation to environmental conditions prevailing in the summer under Isfahan climatic conditions.

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During recent years, several genotypes have been selected from Isfahan land race Kouseh. The performance of safflower selected genotypes was studied in the field conditions, at Agriculture Research Station, Isfahan University of Technology during 2003. The experiment was carried out using a split plot arrangement according to a randomized complete block design with three replications. Planting dates (March 11, April 20, May 22 and June 23) were considered as the main plots and subplots consisted of 20 genotypes of safflower including 19 selections from Kouseh and Arak-2811 genotype. Days from planting to emergence and emergence to stem elongation were reduced as planting was delayed until the fourth planting date. Days from stem elongation to head visible was reduced with delay from the first to the third planting date, and then increased. Days from head visible to 50% flowering was reduced with delay from the first date to the third planting date, but increased in the fourth planting date. Days from 50 percent flowering to physiological maturity was increased with delay in planting. Days from planting to emergence, emergence to stem elongation, stem elongation to head visible and 50 percent flowering to physiological maturity were not influenced by genotypes. Genotype DP7 had the highest and genotype C111 and genotype DP25 had the lowest days from head visible to 50% flowering. The interaction between planting date and genotype in regard to days from stem elongation to head visible was also significant. Seed weight per plant was reduced with delay in planting date. Genotype ISF66 had the highest and genotype Arak-2811 had lowest seed weight per plant. The number of days from emergence to head visible in ISF66, DP5, C128 and Arak-2811 was affected by maximum temperature (Tmax), in genotype DP7 by Tmax², in genotypes DP17, DP1 and C41100 by Tmin² and in genotypes DP9, DP25, ISF28, ISF22, and C111 was affected by day length. It seems that development period from emergence to head visible was affected by temperature in the most genotypes. On March 11 planting date, genotypes had the maximum response to temperature and day length and the minimum response was observed in the fourth planting date. The genotype ISF66 had the highest seed yield on March 11 planting date. The result of this study showed that safflower should be planted in late March under condition similar to this experiment for maximum yield production.