Abstract
The Chloris genus is a C4 photosynthetic species mainly distributed in tropical and subtropical regions. Populations of three Chloris species occurring in citrus orchards from central Cuba, under long history glyphosate-based weed management, were studied for glyphosate-resistant status by characterizing their herbicide resistance/tolerance mechanisms. Morphological and molecular analyses allowed these species to be identified as C. ciliata Sw., Chloris elata Desv., and Chloris barbata Sw. Based on the glyphosate rate that causes 50% mortality of the treated plants, glyphosate resistance (R) was confirmed only in C. elata, The R population was 6.1-fold more resistant compared to the susceptible (S) population. In addition, R plants of C. elata accumulated 4.6-fold less shikimate after glyphosate application than S plants. Meanwhile, populations of C. barbata and C. ciliata with or without glyphosate application histories showed similar LD50 values and shikimic acid accumulation rates, demonstrating that resistance to glyphosate have not evolved in these species. Plants of R and S populations of C. elata differed in 14C-glyphosate absorption and translocation. The R population exhibited 27.3-fold greater 5-enolpyruvyl shikimate-3-phosphate synthase (EPSPS) activity than the S population due to a target site mutation corresponding to a Pro-106-Ser substitution found in the EPSPS gene. These reports show the innate tolerance to glyphosate of C. barbata and C. ciliata, and confirm the resistance of C. elata to this herbicide, showing that both non-target site and target-site mechanisms are involved in its resistance to glyphosate. This is the first case of herbicide resistance in Cuba.
Highlights
The use of herbicides is the most common weed control method (Délye, 2013; Fernández-Moreno et al, 2017b)
Based on the examined morphological traits, the populations studied were identified as C. ciliata Sw., C. elata Desv., and Chloris barbata Sw
Distinctive traits of C. ciliata include a low number of racemes in the inflorescences, more than two sterile florets per spikelet, long keel hairs and relatively short awns
Summary
The use of herbicides is the most common weed control method (Délye, 2013; Fernández-Moreno et al, 2017b). Herbicide resistance has caused this method to be quickly undermined This scenario is the result of evolutionary adaptations in a target weed to herbicide applications (Powles and Yu, 2010; Beckie and Harker, 2017). Glyphosate-Status of Chloris Species from Cuba is one of the most widely used herbicides, it is an herbicide with many cases of resistance (37 glyphosateresistant species; Shaner et al, 2012; Bracamonte et al, 2016; Heap, 2017). Non-target-site resistance (NTSR) mechanism results from reduced absorption and/or translocation, increased vacuolar sequestration, and metabolism to non-toxic compounds, causing less glyphosate transport to the EPSPS via the xylem and phloem (Délye, 2013). Similar to TSR, NTSR has been found to be a mechanism involved in resistance in many weeds (de Carvalho et al, 2012; Ge et al, 2012; Rojano-Delgado et al, 2012; Vila-Aiub et al, 2012)
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