Assessment of the Phytotoxic Effects of the Herbicide Metsulfuron-Methyl on Cow-pea at the Morphological and Biochemical Levels

Abstract

Herbicides like sulfonylureas are widely used, but they can persist in the soil and harm unintended plants. In this study, we examined how metsulfuron-methyl (MSM) affects cowpea (Vigna unguiculata) by measuring changes in plant growth and chemical processes. We focused on seed germination and early seedling growth. We tested four MSM concentrations: 0, 100, 200, and 300 mg per liter. For the germination test, we used Petri dishes and treated healthy, sterilized seeds with these concentrations. For other growth and biochemical tests, we used plastic cups in which we sowed uniform healthy seeds after surface sterilization. We applied foliar sprays of MSM at different con-centrations to 15-day-old plants at the three-leaf stage. We applied the leaf sprays when plants had three leaves, 15 days after planting. We measured plant growth and leaf green pigment 30 days after planting. We analyzed the data using one-way ANOVA and Tukey's HSD test at P ≤ 0.05. MSM application significantly inhibited germination, veg-etative growth, and chlorophyll accumulation in a concentration-dependent manner. Germination rates declined from 93% in the control group to 66% at 300 mg L⁻¹. Furthermore, shoot length decreased by 68% at 300 mg L⁻¹ relative to the control. Chlorophyll levels declined in MSM-treated plants. Treatment with 200 mg L-1 resulted in a 53% reduction in chlorophyll a and up to a 60% reduction in chlorophyll b compared to untreated plants. Total chlorophyll content was also reduced by 55% at 200 mg L-1 MSM relative to the control. Notably, plants treated with 300 mg L-1, which were already desiccated at the time of sampling, exhibited no detectable chlorophyll. A similar case was also reported for biomass accumulation: no fresh biomass was observed at 30 mg L-1 MSM because the plant was already dry. As herbicide concentration increased, root growth, leaf number, and leaf area all dropped significantly. This shows that cowpea is highly sensitive to MSM during the early seedling stage. The results indicate that herbicide application can pose risks to non-target plant organs. To promote sustainable plant growth, clear criteria and precautions should be established to safeguard these organs from adverse effects.