Effects of glyphosate on seed germination and early growth of weeds (Sorghum bicolor and Sorghum sudanense)

Abstract

Glyphosate is recognized as an effective herbicide because of its ability to suppress various weeds. However, its potential effects on seed germination and early growth of weeds are not fully understood. The novelty of this research lies in examining seed germination and early growth responses of weeds exposed to glyphosate, aiming to optimize glyphosate application rates in agricultural fields while minimizing environmental impacts. This study investigated the effects of glyphosate on the germination and early growth of two major weeds commonly found in paddy fields, Sorghum bicolor and Sorghum sudanense. Seeds were exposed to a range of glyphosate concentrations; 0.0 ppm (control), 0.1 ppm, 0.3 ppm, 0.5 ppm, 0.7 ppm, 0.9 ppm, 1 ppm and 2 ppm, including environmentally realistic concentrations, for eight days. Seed germination, morphometric and morphological changes were recorded daily. In the control treatments, seed weight increased by approximately 50 mg and 30 mg for S. bicolor and S. sudanense, respectively. In contrast, S. sudanense exhibited a reduction in seed weight, ranging from -1.66 mg to -0.65 mg across treatments, while S. bicolor showed a consistent increase (~10 mg) under all treatments. The length of emerging leaves in the control set up reached up to 2.0 cm and 3.5 cm, respectively, in S. bicolor and S. sudanense, but was restricted to 0.6 cm under glyphosate treatments for both species. Similarly, root length reached 2 cm and 3 cm in S. bicolor and S. sudanense, respectively, in controls, whereas the maximum recorded root length under treatments was only 0.2 cm for both species. Statistical analyses (ANOVA) revealed significant differences (p < 0.05) between control and treatment groups for all assessed parameters. A glyphosate concentration of 25 ppm completely inhibited seed germination in both species. These findings improve our understanding of glyphosate's role in weed management and highlight its potential environmental implications.