Effects of glyphosate on the mortality and shikimic acid level in two goosegrass [Eleusine indica (L.) Gaertn.] biotypes

B.S. Ismail*, C.W. Chee* and S. Salmijah*

Abstract

The status of glyphosate resistance in Eleusine indica [L.] Gaertn. biotypes collected from two different areas namely, Lenggeng and Bidor as compared to a known susceptible biotype from CCM Bioscience Agrochemicals Research Centre (BRC), Malaysia was determined. Involvement of 5-enolpyruvylshikimate- 3 phosphate synthase (EPSPS) in the glyphosate-resistant biotype was investigated through the measurement of the shikimic acid content. Using glyphosate at doses ranging from 0.27–16.00 kg a.i./ha, the Bidor biotype was 7-fold more resistant than the BRC and Lenggeng biotypes. The resistance status of the Bidor biotype was confirmed by a much lower shikimic acid accumulation compared to the BRC and Lenggeng biotypes. There was no significant difference (p >0.05) between shikimic acid accumulation in the leaves and stems at lower doses of glyphosate. At higher doses of glyphosate (1.44 –16.00 kg a.i./ha for BRC and Lenggeng biotypes; 7.20 –16.00 kg a.i./ha for Bidor biotype), shikimic acid accumulation was detected to be higher in the leaves than in the stems (*p <0.05). While EPSPS in the leaves and stems were both inhibited at lower doses, self-limitation probably impaired glyphosate translocation from the leaves to the stems at higher doses. Therefore, leaves were the likely major inhibition sites at high glyphosate concentrations.

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