Thermodynamic Characterisation 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 plantsare tolerant to some herbicides. The aim of our experiment was to study susceptibility of16 ZP lines to nicosulfuron and foramsulfuron 48 hours after application in the 2006-2009period. The alterations in dry matter content, as well as thermodynamic parameters of freeenergy and enthalpy, were analyzed. The examined parameters show that season had a significantinfluence on phytotoxicity expression, with high EWRC values obtained togetherwith high values of free energy and dry matter during the cold season with lower precipitationlevel (period after herbicide application). In susceptible lines, the phytotoxic effectinduced an increase in dry matter and free energy. Phytotoxic effects of nicosulfuron andforamsulfuron have basically different impact on system energetic properties: the effects ofnicosulfuron could be connected to greater energy consumption, and the effects of foramsulfuronto increasing potential energy, mainly from metabolism, which could be associatedwith a “metabolic burst”. From that point of view, the examined parameters can be successfullyused as indicators of herbicide stress immediately after application.