Physiological response of ryegrass (Lolium spp.) grown at different temperatures to glufosinate ammonium application

Abstract

Efficacy of glufosinate ammonium is influenced by temperature. However, several studies show variable results. The response of ryegrass (Lolium spp.) to glufosinate ammonium activity at different temperatures was investigated. Ryegrass was grown at 10/15, 15/20, 20/25, and 25/30 °C (night/day) temperature regimes. Ammonia accumulation, glutamine synthetase, glutamate dehydrogenase, and nitrate reductase activity was analysed on control plants (0 g a.i. ha⁻¹) and treated plants (900 g a.i. ha⁻¹) 24 hours after application (HAA). Photosynthesis studies were conducted on plants treated with 0 and 900 g a.i. ha⁻¹ glufosinate ammonium dosage rates 24, 48, and 72 HAA using an infra-red gas analyser. An increase in glutamine synthetase enzyme activity was observed with increasing temperature after glufosinate ammonium application. In contrast, glutamine dehydrogenase enzyme activity decreased with increasing temperature in treated plants. Accumulation of ammonia was not the main cause of ryegrass mortality. Better control of ryegrass with glufosinate ammonium at cooler temperatures was mainly attributed to the rapid decline in glutamine synthetase activity 24 HAA.