Glyphosate Resistance in Amaranthus viridis in Brazilian Citrus Orchards

Ricardo Alcántara-De La Cruz,Leonardo Bianco De Carvalho,Luiz Renato Rufino,Maria Fátima Das Graças Fernandes Da Silva Silva,Gabriel Da Silva Amaral,Fernando Alves De Azevedo,Guilherme Moraes De Oliveira

doi:10.3390/agriculture10070304

Abstract

Glyphosate is the main tool for weed management in Brazilian citrus orchards, where weeds, such as Conyza bonariensis and Digitaria insularis, have been found with resistance to this herbicide. Field prospections have allowed the identification of a possible new case of glyphosate resistance. In this work, the susceptibility levels to glyphosate on three Amaranthus viridis L. populations, with suspected resistance (R1, R2, and R-IAC), collected in citrus orchards from the São Paulo State, Brazil, as well as their accumulation rates of shikimic acid, were determined. The fresh weight of the susceptible population (S) was reduced by 50% (GR50) with ~30 g ea ha−1 glyphosate, while the GR50 values of the R populations were between 5.4 and 11.3 times higher than that for S population. The LD50 (herbicide dose to kill 50% of individuals of a weed population) values of the S population were ≤150 g ea ha−1 glyphosate, while the LD50 of the R populations ranged from 600 to 920 g ea ha−1. Based on the reduction of fresh weight and the survival rate, the R1 population showed the highest level of glyphosate resistance, which had GR50 and LD50 values of 248 and 918 g ea ha−1 glyphosate, respectively. The S population accumulated 240 µg shikimic acid at 1000 µM glyphosate, while the R1, R2, and R-IAC populations accumulated only 16, 43, and 33 µg shikimic acid, respectively (between 5.6 to 15 times less than the S population). Enzyme activity assays suggested that at least one target site-type mechanism was involved in resistance. This result revealed the first report of glyphosate resistance in A. viridis reported in the world.

Highlights

Brazil is the world’s largest producer and exporter of citrus [1]
The fresh weight reduction was higher in individuals of the S-Lim slender amaranth population than the R populations
After repetition of dose-response experiments, more representative value of GR50 was estimated for the population S-Lim (38 g ea ha−1 ) due to the smaller dose of glyphosate included; while the GR50 values of the R populations were similar to those estimated in the first experiment

Summary

Introduction

Brazil is the world’s largest producer and exporter of citrus [1]. The State of São Paulo (SP)accounts for ~77% of the national production of orange (Citrus sinensis (L.) Osbeck), being the main exporter of concentrated orange juice [2]. Brazil is the world’s largest producer and exporter of citrus [1]. Accounts for ~77% of the national production of orange (Citrus sinensis (L.) Osbeck), being the main exporter of concentrated orange juice [2]. The yield of citrus fruit is not the best in the world, mainly due to improper management of the plantations by growers [3]. 27.6 tons ha−1 , occupying the 13th world rankings [4]. Weed presence can be directly or indirectly responsible for up to 30–52% of yield losses in citrus orchards of young and growing trees [3,5].

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Discussion

Conclusion