The Effect of Glyphosate Concentration and Exposure Time on Sucrose Accumulation and Various Physical-Physiological Parameters in Sugarcane (Saccharum officinarum Linn.)

Abstract

Due to climate change, sugar yield has been significantly decreasing, resulting in an increase in its domestic price. Thus, methods to counter this problem and increase sugar yield are very timely. Widely used today by other countries is the application of low doses of herbicides, such as glyphosate, as a ripener. Glyphosate has been reported to stunt growth but allow accumulation of sucrose in the culm. To test if there would be a significant increase in sucrose concentration in the culm, glyphosate was applied in three different concentrations, namely, 240g active ingredient/hectare, 480g a.i./ha and 720g a.i./ha with distilled water as control, on 21-week old sugarcane plants in a field site in Alitagtag, Batangas. The change in height, culm weight and volume of raw juice relative to culm weight were measured 4, 6 and 8 weeks after treatment. Also, chlorophyll concentration and sucrose concentration were measured using DMSO extraction method and DNS sucrose assay, respectively. Results showed that glyphosate hampered the apical growth and biomass accumulation of the culm and therefore, caused a significant increase in the sucrose content of the samples. Glyphosate may have caused the reduction in the activity of acid invertase and sucrose synthase which inhibited the hydrolysis of sucrose into hexoses. Moreover, an increase in chlorophyll content was recorded from the third leaf samples of the plants treated with higher concentrations of the herbicide. This could be attributed to the formation of new sink organs by the growing samples, which needed an allocation of the stored reserves from the leaf. This resulted in the breakdown of chlorophyll to be mobilized to the newly formed leaves of the plant. It was concluded that the most suitable concentration of glyphosate and the optimal harvesting time was 720g a.i./ha and 8 weeks after treatment, respectively.