Effects of ethephon on growth and yield of sweet sorghum (Sorghum bicolor L. Moench) at different growth stages

There is little information about the effects of ethephon ripening hormone on the yield of sweet sorghum in Thailand. Therefore, this study aimed to evaluate the impact of ethephon hormone applied at different growth stages of three cultivars of sweet sorghum on its growth and yield. The experiment was conducted from December 2016 to May 2017 at a research plot of the Faculty of Agricultural Technology, King Mongkut's Institute of Technology Ladkrabang, Bangkok, Thailand. The experiment was designed as a split-plot design with three replications. Three sweet sorghum cultivars (Ethanol 2, KKU 40, and Cowley) were planted in the main plot. Ethephon was applied at five stages of growth of these cultivars: heading stage, panicle stage, milking stage, dough stage, harvesting stage. Ethephon applications at those stages and untreated control were the subplots. Results showed that Ethanol 2 cultivar exhibited a higher growth rate, plant height, stem diameter, grain yield, stem fresh weight, and yield, juice extract yield, and sugar content than those exhibited by KKU 40 and Cowley. Application of ethephon at the heading stage gave the lowest stem diameter, grain yield, stem fresh weight, and yield, whereas applying it at the harvesting stage gave the highest sugar yield. There were no significant correlations between sweet sorghum cultivars and the growth stages at which ethephon was applied. Based on these results, it might be concluded that Ethanol 2 cultivar should be treated with ethephon hormone at its harvesting stage.