ACCUMULATION OF SHIKIMIC ACID - A TECHNIQUE FOR SCREENING GLYPHOSATE EFFICACY

Biochemical changes in leaves of 3-week-old oil seed rape (Brassica na pus L. cv. Iris) plants were determined shortly after treatment with d ifferent doses of glyphosate. Secondary effects of N-(phosphonomethyl) glycine (glyphosate) on activity of the enzyme phenylalanine ammonia-l yase was not related to dose of glyphosate by any known model within t he first 48 h after spraying. Accumulation of shikimic acid was relate d to the dose of glyphosate by a nonlinear logistic dose-response mode l-as early as 5 h after spraying. Within the same period shikimic acid accumulation made it possible to distinguish between a formulation of the pure isopropylamine salt of glyphosate and formulations containin g different surfactants. ED50 estimates based on accumulation of shiki mic acid gave a good indication of the relative strength of the evalua ted glyphosate formulations. Ranking of ED50 based on accumulation of shikimic acid was the same as achieved by visual assessment of plant d eath 14 days after spraying.