Thiamethoxam as a seed treatment alters the physiological response of maize (Zea mays) seedlings to neighbouring weeds

Abstract

Thiamethoxam is a broad-spectrum neonicotinoid insecticide that, when applied to seed, has been observed to enhance seedling vigour under environmental stress conditions. Stress created by the presence of neighbouring weeds is known to trigger the accumulation of hydrogen peroxide (H2 O2 ) in maize seedling tissue. No previous work has explored the effect of thiamethoxam as a seed treatment on the physiological response of maize seedlings emerging in the presence of neighbouring weeds. Thiamethoxam was found to enhance seedling vigour and to overcome the expression of typical shade avoidance characteristics in the presence of neighbouring weeds. These results were attributed to maintenance of the total phenolics content, 1,1-diphenyl-2-picryl-hydrazyl (DPPH) radical scavenging activity and anthocyanin and lignin contents. These findings were also associated with the activation of scavenging genes, which reduced the accumulation of H2 O2 and the subsequent damage caused by lipid peroxidation in maize seedlings originating from treated seeds even when exposed to neighbouring weeds. These results suggest the possibility of exploring new chemistries and modes of action as novel seed treatments to upregulate free radical scavenging genes and to maintain the antioxidant system within plants. Such an approach may provide an opportunity to enhance crop competitiveness with weeds.