Determination of Conyza canadensis Levels of Sensitivity to Glyphosate Trimesium Sulphosate

Abstract

Changes in leaf anatomy were examined in two S. African populations of Conyza canadensis of which one was presumed to be resistant (CCPR) and the other susceptible (CCS) to glyphosate. Glyphosate was applied to plants, which were grown from seed collected from these populations, at rates of 1, 2 and 4 kg a.e. ha(-1) of TOUCHDOWN [active substance: glyphosate trimesium salt, 500 g L-1] that are equivalent to 2, 4 and 8 L ha (-1) of the herbicide Touchdown. Leaf samples for the light microscope (LM) analysis were collected 3, 7 and 24 h after treatment (HAT). Changes in chlorophyll and shikimate content of leaf material were also examined. Changes in the palisade and pith tissue of leaves were not detected in the investigated populations at 3 and 7 HAT. However, at 24 HAT the different herbicide doses caused changes in leaf anatomy. These changes (injuries) were detected in the CCS at all tested doses, but in the CCPR population of C. canadensis the injuries were observed at only the two highest rates, 2 and 4 kg a.e. ha(-1). Chlorophyll and shikimate contents indicated significant differences between the treated and untreated plants of susceptible population only. Difference in glyphosate resistance between the CCS and CCPR populations was confirmed with an index of resistance of 1.58. This value of the index of resistance indicates that CCS population is 1.58 times more susceptible to glyphosate compared to CCPR population. (C) 2013 Friends Science Publishers