Abstract
Glyphosate has been used for more than 15 years for weed management in citrus groves in the Gulf of Mexico, at up to 3–4 applications per year. Goosegrass (Eleusine indica (L.) Gaertn.) control has sometimes failed. In this research, the mechanisms governing three goosegrass biotypes (Ein-Or from an orange grove, and Ein-Pl1 and Ein-Pl2 from Persian lime groves) with suspected resistance to glyphosate were characterized and compared to a susceptible biotype (Ein-S). Dose-response and shikimate accumulation assays confirmed resistance of the resistant (R) biotypes. There were no differences in glyphosate absorption, but the R biotypes retained up to 62–78% of the herbicide in the treated leaf at 96 h after treatment (HAT), in comparison to the Ein-S biotype (36%). The 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) activity in the Ein-Or and Ein-S biotypes was over 100-fold lower than the Ein-Pl1 and Ein-Pl2 ones. The latter showed a high EPSPS-basal activity, a mutation at Pro-106-Ser position in the EPSPS gene, and EPSPS overexpression. The EPSPS basal and EPSPS overexpression were positively correlated. The R goosegrass biotypes displayed poor glyphosate translocation. Furthermore, this grassweed showed, for the first time, two mechanisms at the target-site level (Pro-106-Ser mutation + EPSPS overexpression) acting together simultaneously against glyphosate.
Highlights
Goosegrass (Eleusine indica (L.) Gaertn.), an annual-C4 summer grass plant, is one of the world’s worst weeds
Some resistant grassweed species presenting enolpyruvylshikimate-3-phosphate synthase (EPSPS) copy numbers and/or overexpression as glyphosate resistance mechanisms are as follows: B. diandrus[45], Kochia scoparia[44] and L. perenne[42, 46]. These results indicate that the Ein-Pl1 and Ein-Pl2 goosegrass biotypes from Persian lime groves have evolved a mutation and overexpression of the target site, which gives them greater resistance to glyphosate due to the different selection pressure exerted by this herbicide in these groves compared to the orange groves
Goosegrass presents a great adaptive capacity to develop herbicide resistance, making it one of the most harmful weeds in agriculture; this weed was the first to achieve the following: evolved single Pro-1061 and double Thr-102-Ile + Pro-106-Ser[4, 16] mutations that confer resistance to glyphosate; exhibited multiple resistance to non-selective herbicides[8], and the current methodologies do not allow determination of the NTRS and target site resistance (TSR) mechanisms involved in their resistance to glufosinate[49]; and we demonstrated that goosegrass can be expressed by two mechanisms simultaneously at the target site level against glyphosate
Summary
Goosegrass (Eleusine indica (L.) Gaertn.), an annual-C4 summer grass plant, is one of the world’s worst weeds. It comes from Africa and is widely spread over tropical, subtropical regions and temperate regions of the world[1, 2]. Glyphosate inhibits EPSPS, disrupting the biosynthesis of phenylalanine, tyrosine, tryptophan and others secondary aromatic products[10]. The objectives of this study were as follows: 1) to confirm resistance of goosegrass to glyphosate; and 2) to study the resistance mechanisms involved in the resistant biotypes collected from citrus fruit groves in Mexico
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