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.
