Evolution of Target-Site Resistance to Glyphosate in an Amaranthus palmeri Population from Argentina and Its Expression at Different Plant Growth Temperatures.

Kaundun Kaundun,Marchegiani Marchegiani,Tuesca Tuesca,Galloway Galloway,Hutchings Hutchings,Moreno Moreno,Mcindoe Mcindoe,Jackson Jackson,Howell Howell,Carlin Carlin

doi:10.3390/plants8110512

Abstract

The mechanism and expression of resistance to glyphosate at different plant growing temperatures was investigated in an Amaranthus palmeri population (VM1) from a soybean field in Vicuña Mackenna, Cordoba, Argentina. Resistance was not due to reduced glyphosate translocation to the meristem or to EPSPS duplication, as reported for most US samples. In contrast, a proline 106 to serine target-site mutation acting additively with EPSPS over-expression (1.8-fold increase) was respectively a major and minor contributor to glyphosate resistance in VM1. Resistance indices based on LD50 values generated using progenies from a cross between 52 PS106 VM1 individuals were estimated at 7.1 for homozygous SS106 and 4.3 for heterozygous PS106 compared with homozygous wild PP106 plants grown at a medium temperature of 24 °C day/18 °C night. A larger proportion of wild and mutant progenies survived a single commonly employed glyphosate rate when maintained at 30 °C day/26 °C night compared with 20 °C day/16 night in a subsequent experiment. Interestingly, the P106S mutation was not identified in any of the 920 plants analysed from 115 US populations, thereby potentially reflecting the difference in A. palmeri control practices in Argentina and USA.

Highlights

Differential uptake was not a contributor to glyphosate resistance in the VM1 A. palmeri population, contrary to what was reported in a few Lolium multiflorum, Digitaria insularis, Bidens pilosa, Amaranthus palmeri, Sorghum halepense, Chloris elata and Leptochloa virgata populations [22,28,29,30,31,32]
Reduced movement to actively growing meristematic tissues identified in a wide range of Conyza spp., Lolium spp., Amaranthus spp., Chloris elata and Eleusine indica samples was not associated with resistance to glyphosate in VM1 [33,34,35,36]
The enolpyruvylshikimate-3-phosphate synthase (EPSPS) copy number in A. palmeri VM1 was comparable to the standard sensitive population ApS, both clearly differentiated from the standard resistant population

Summary

Introduction

United States and northern Mexico [1] It is a tall, erect, annual, summer species capable of attaining heights of two metres [2]. Erect, annual, summer species capable of attaining heights of two metres [2] It was once cultivated and eaten by Native Americans including the Navajo, Pima, Yuma and Mohave for its highly nutritious leaves, stems and seeds [3]. Several attributes have contributed to the success of A. palmeri as a highly adaptable and invasive weed. It is a C4 species with a very high photosynthetic rate and water use efficiency [5,6]. When Palmer amaranth co-emerges with soybean, a single plant per 30 cm of row reduced grain yield by as much as 64%, according to a field study in Arkansas [10]

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Methods

Conclusion