Cross- and multiple herbicide resistance in Lolium multiflorum across Uruguay.

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From: Weed Research(Vol. 62, Issue 4)
Publisher: Wiley Subscription Services, Inc.
Document Type: Report
Length: 527 words

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Keywords: herbicide-resistant ryegrass; resistance evolution; resistance screening; South America Abstract Herbicide resistance is currently one of the most important problems in agricultural systems, threatening their sustainability. In Uruguay, there have been increasing reports of herbicide failures to control LOLMU (Lolium multiflorum Lam.) populations. However, methodical characterization of herbicide resistance cases is lacking. Seeds from 66 LOLMU populations were collected from cropping fields and screened in greenhouse conditions with the recommended (1×) and half the recommended (1/2×) label dose of glyphosate, clethodim, pinoxaden and a formulation with iodosulfuron-methyl-sodium and mesosulfuron-methyl (IodoMeso). Populations were classified as resistant when mortality was equal to or lower than 80% in response to 1× doses, assessed 28days after treatment (DAT). Results show that 80% of LOLMU populations were resistant to glyphosate, followed by 49%, 36% and 24% resistance to IodoMeso, pinoxaden and clethodim respectively. Moreover, 52% of the tested populations were resistant to more than one herbicide, with an important frequency of populations resistant to glyphosate and IodoMeso (17%) and to all tested herbicides (16%). In addition, a high correlation of resistance levels was found between pinoxaden and clethodim resistant populations (R.sup.2 = 0.84). Geographic distribution of tested populations suggests that multiple herbicide resistance is concentrated in fields with a longer history of herbicide use. Overall, these results confirm that herbicide resistance in LOLMU is widespread in agricultural regions of Uruguay and that significant number of multiple resistance cases already exist and are expected to increase rapidly if management practices are not adjusted quickly and substantially. This survey represents a key input to improve herbicide-resistant LOLMU management strategies. Article Note: Subject Editor: Maor Matzrafi, Volcani Institute, Ramat-Yishay, Israel Funding information Instituto Nacional de Investigacion Agropecuaria, Uruguay CAPTION(S): Table S1 Questionnaire sent to farmers/technician for each sampled field. Table S2. Statistical significance (P-value) of each factor effect in mortality response (GLM model) and growth reduction response (LM-GLS model) at label doses (1×) for each herbicide treatment showed in the anova (n = 3). Table S3. Percentage of the tested Lolium multiflorum populations that were perceived to be resistant by farmers and that were categorised as resistant after the screening for each herbicide (n = 51). Figure S1. Growth reduction 28 DAT in Lolium multiflorum populations treated with the recommended label dose (1×) of glyphosate (A), clethodim (B), pinoxaden (C) and iodosulfuron/mesosulfuron mixture (D). Small dashes represent the average weight of shoot fresh biomass in three pots containing 15 plants each and error bars indicate the range from lower to upper 95% confidence limit. Figure S2. Farmer's answers (n = 51 fields) on: Number of years the field received the herbicide that fails to control Lolium multiflorum (problem herbicide) (A) and number of times per year the problem herbicide is regularly applied (B). Figure S3. Growth reduction 28 DAT in Lolium multiflorum populations treated with the recommended label dose (1×) of glyphosate (A), clethodim (B), pinoxaden (C) and iodosulfuron/mesosulfuron mixture (D). Small dashes represent the average weight of shoot dry biomass in three pots containing 15 plants each and error bars indicate the range from lower to upper 95% confidence limit. Byline: Sofía Marques Hill, Martin Vila-Aiub, Manuel Hernández, Tiago E. Kaspary, Milton A. García

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Gale Document Number: GALE|A710975372