Abstract
The gene sequence encoding 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS), the enzymatic target site of the herbicide glyphosate, was determined for several purple nutsedge (Cyperus rotundus L.) accessions from geographically distant locations and these were aligned to generate a consensus sequence. The EPSPS sequences each had single nucleotide polymorphisms (SNPs) only a few of which were predicted to cause an amino acid change in the EPSP synthase. None had the proline to serine substitution or other substitutions responsible for glyphosate resistance reported in other species. A dendrogram generated from the cluster analysis of the EPSPS gene sequences indicated similarities between accessions from Tanzania, Indonesia, California-2, Greece, Brazil, Argentina and Iran much like cluster analysis previously reported based on RAPD scores and morphological traits possibly indicating a common genetic background or origin. Considering the differences in EPSPS sequences, the response of these purple nutsedge accessions to 0.84 kg·ae·ha-1 of glyphosate was assessed to determine whether differential tolerance was present. At 7 days after the first application control ranged from 9% for the accession from Greece to 73% for the accession from Tanzania. Control of these accessions increased to 45% and 93% respectively by 14 days after the second application. The I50’s for glyphosate inhibition of growth for four accessions from geographically distant countries (Mississippi, Brazil, Indonesia and Tanzania) were 0.21, 0.10, 0.25 and 0.06 kg·ha-1, respectively, which represented a 4-fold difference. The difference in sensitivity to glyphosate may be a result of a non-target site mechanism such as differences in sequestration, translocation or cuticle thickness rather than alterations in EPSPS.
Highlights
Purple nutsedge (Cyperus rotundus L.) is a perennial weed that can reduce yields in many crops by depleting soil moisture and nutrients as well as by releasing allelopathic compounds that inhibit growth of neighboring plants [1]
A dendrogram generated from the cluster analysis of the enolpyruvylshikimate-3-phosphate synthase (EPSPS) gene sequences indicated similarities between accessions from Tanzania, Indonesia, California-2, Greece, Brazil, Argentina and Iran much like cluster analysis previously reported based on random amplified polymorphic DNA (RAPD) scores and morphological traits possibly indicating a common genetic background or origin
This study aimed to determine whether there were EPSPS sequence variations among purple nutsedge accessions collected from diverse locations around the world, and if so, were the variations conserved between neighboring or regionally close countries
Summary
Purple nutsedge (Cyperus rotundus L.) is a perennial weed that can reduce yields in many crops by depleting soil moisture and nutrients as well as by releasing allelopathic compounds that inhibit growth of neighboring plants [1]. It has been found in 92 countries and is a problematic weed in 52 crops [1] [2] [3]. Purple nutsedge might be expected to be genetically and morphologically diverse considering its worldwide distribution, it reproduces primarily by asexual means from tubers and rhizomes and rarely produces viable seed [4] [5]. Tubers may survive for 42 months in the soil and each can give rise to several rounds of shoot, root and rhizome formation [5] [8]
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