Glyphosate Resistance in Tridax procumbens via a Novel EPSPS Thr- 102-Ser Substitution

This paper is a collaborative effort with researchers coming from China to AHRI and with modelling from Alex Nyporko from Kiev, Ukraine. Lead author Dr Jingbo Li from Hunan University and second author Dr Qiong Peng were visiting fellows in AHRI supported by the China Scholarship Council.

In this research, it was first established that Tridax, a global tropical weed species, evolved glyphosate resistance in the Ord River irrigation area in north-western Western Australia.

This is the first report of glyphosate resistance in Tridax. The mechanism of glyphosate resistance was studied. Various possible resistance mechanisms were NOT responsible for resistance (EPSPS gene amplification, different glyphosate uptake or translocation). In this glyphosate-resistant Tridax population, the glyphosate resistance mechanism is a mutation in the EPSPS gene causing substitution at amino acid 102 (Thr-102-Ser).

This is the first time that a single amino acid substitution at Thr 102 has been reported to endow glyphosate resistance. Note that Tridax is a tetraploid and this Thr-102-Ser amino acid substitution, as expected in a tetraploid species, confers only a modest level of glyphosate resistance.

This finding of a resistance endowing amino acid substitution at amino acid 102 adds to the many reports of glyphosate resistance due to amino acid substitutions at Proline 106. The 102 site is within the highly conserved and catalytically important EPSPS region.

We have previously reported in Eleusine that a double mutation at amino acids 102 and 106, the TIPS mutations, confer high-level glyphosate resistance but at substantial fitness cost (Yu et al Plant Physiology 2015).