Department of Biology, Faculty of Science, University of Isfahan, Isfahan-81846-73441, Iran.
In this study, the effects of concentration and application time of ethephon on growth parameters; stem height, stem diameter, biomass, carbohydrate content; sucrose content, invert sugar, brix value, and juice volume of two sweet sorghum cultivars were determined. Three ethephon application time (8 leaves, booting, and flowering) and five ethephon concentrations (0, 200, 400, 600, and 800 ppm) on two sweet sorghum cultivars (Sofra and Keller), were deigned in a split-split plot with three replications. Hormone application time assessed as main plot, cultivars as sub plot and ethephon concentrations as sub-sub plots. Brix was shown the maximum amount (16.7%) at booting stage while it was not significant at the other two stages of hormone application time (15%). The lowest biomass was (21.5 t ha-1) at 8 leaves stage and the highest (46 t ha-1) at flowering stage. Similar to biomass the lowest juice volume was (3650 L ha-1) at the 8 leaves stage of the hormone application time and highest (8000 L ha-1) at the flowering. Sucrose content was significantly affected (P<0.01) by the treatment. It was higher at booting stage (11.84%) than both 8 leaves stage and flowering stage (10.7%). cv. Keller had higher stem height, brix, and sucrose content than Sofra while its invert sugar was lower than Keller. Based on these results, to have the highest brix value it may be suggested to apply ethephon at 800 ppm at flowering stage in both sweet sorghum Keller and sofra cultivars.