Thermodynamic characterization of early phytotoxic effects of sulfonylurea herbicides to maize lines

Variations in susceptibility of maize lines to herbicides depend on different factors. Visible signs of phytotoxicity do not occur in the first few days after application when plants are tolerant to some herbicides. The aim of our experiment was to study susceptibility of 16 ZP lines to nicosulfuron and foramsulfuron 48 hours after application in the 2006-2009 period. The alterations in dry matter content, as well as thermodynamic parameters of free energy and enthalpy, were analyzed. The examined parameters show that season had a significant influence on phytotoxicity expression, with high EWRC values obtained together with high values of free energy and dry matter during the cold season with lower precipitation level (period after herbicide application). In susceptible lines, the phytotoxic effect induced an increase in dry matter and free energy. Phytotoxic effects of nicosulfuron and foramsulfuron have basically different impact on system energetic properties: the effects of nicosulfuron could be connected to greater energy consumption, and the effects of foramsulfuron to increasing potential energy, mainly from metabolism, which could be associated with a “metabolic burst”. From that point of view, the examined parameters can be successfully used as indicators of herbicide stress immediately after application. [Projekat Ministarstva nauke Republike Srbije, br. TR-31037]