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Eleusine indica (goosegrass) is a diploid grass weed which has developed resistance to ACCase inhibitors during the last ten years due to the intensive and frequent use of sethoxydim to control grass weeds in soybean crops in Brazil. Plant dose-response assays confirmed the resistant behaviour of one biotype obtaining high resistance factor values: 143 (fenoxaprop), 126 (haloxyfop), 84 (sethoxydim) to 58 (fluazifop). ACCase in vitro assays indicated a target site resistance as the main cause of reduced susceptibility to ACCase inhibitors. PCR-generated fragments of the ACCase CT domain of the resistant and sensitive reference biotype were sequenced and compared. A point mutation was detected within the triplet of aspartate at the amino acid position 2078 (referred to EMBL accession no. AJ310767) and resulted in the triplet of glycine. These results constitute the first report on a target site mutation for a Brazilian herbicide resistant grass weed.

Eleusine indica (goosegrass) is a diploid grass weed which has developed resistance to ACCase inhibitors during the last ten years due to the intensive and frequent use of sethoxydim to control grass weeds in soybean crops in Brazil. Plant dose-response assays confirmed the resistant behaviour of one biotype obtaining high resistance factor values: 143 (fenoxaprop), 126 (haloxyfop), 84 (sethoxydim) to 58 (fluazifop). ACCase in vitro assays indicated a target site resistance as the main cause of reduced susceptibility to ACCase inhibitors. PCR-generated fragments of the ACCase CT domain of the resistant and sensitive reference biotype were sequenced and compared. A point mutation was detected within the triplet of aspartate at the amino acid position 2078 (referred to EMBL accession no. AJ310767) and resulted in the triplet of glycine. These results constitute the first report on a target site mutation for a Brazilian herbicide resistant grass weed. Eleusine indica (ELEIN) é uma espécie monocotiledônea, diploide. No Brasil, ela desenvolveu resistência aos inibidores da ACCase durante os últimos dez anos, devido ao uso intensivo e frequente desses graminicidas para controlar plantas daninhas em lavouras de soja. Experimentos de dose-resposta realizados com a planta confirmaram a resistência de um biótipo. Houve elevada tolerância aos herbicidas, com fatores de resistência da ordem de 143 (fenoxaprop), 126 (haloxyfop), 84 (sethoxydim) e 58 (fluazifop). Ensaios com a enzima ACCase in vitro indicaram a insensibilidade desta como a principal causa de suscetibilidade reduzida a esses herbicidas. Fragmentos de PCR gerados do domínio CT da enzima ACCase dos biótipos resistente e sensível de referência foram sequenciados e comparados. Foi detectada uma mutação dentro do tripleto de asparagina na posição do aminoácido 2078 (referente ao acesso número AJ310767 no EMBL), que resultou no tripleto de glicina. Esses resultados constituem o primeiro caso de uma mutação em ACCase em uma espécie daninha gramínea do Brasil.

Greenhouse and laboratory experiments were conducted to investigate two Lolium spp. populations from a northern Italian vineyard (biotype "R-332") and a southern Italian olive grove (biotype "R-336") that were not controlled by the registered rates of glyphosate. The fraction of resistant (R) plants of each population was determined through screenings using two doses of glyphosate and three doses of ACCase inhibitors: cycloxydim and fluazifop. Shikimate accumulation at two doses was measured spectrophotometrically at 24, 48, 72, 96 and 216 hours after treatment. A quick germination dose-response test in petri dishes using glyphosate solutions at different concentrations was set up to select the R individuals within the population for further investigations. The R seedlings were discriminated on the basis of shoot and root development. The screening results confirmed resistance outlining the following profile for the northern R-332 biotyope: 84% (Standard Error 1.4) and 56% (3.2) of survivors and 104% (6.6) and 43% (3.7) of fresh weight at lower (360 g a.e. ha-1) and higher doses (1440 g a.e. ha-1) respectively, referred to the untreated check. Southern R-336 biotype: 98% (0.25) and 88% (3.1) of survivors and 110% (2.9) and 60% (3.5) of fresh weight. Both ACCase inhibitors controlled the glyphosate resistant biotypes. The shikimate accumulation clearly discriminated the R populations from the susceptible (S-204) at the lower dose while at the maximum dose applied the northern population had an accumulation comparable to the S pop but R plants fully recovered in 21 days. The southern population did not accumulate shikimate as the S population neither at the higher level. The quick test outlined a concentration above 100 ?M to discriminate S from R populations.

Glyphosate is the world's most widely used herbicide, with many registrations in agricultural, urban and semi-natural environments. Glyphosate is an important tool especially for broad-spectrum weed control and inter-row vegetation management in perennial crops like olive and citrus groves, orchards and vineyards. Despite the frequent use in these crops, there are only a few confirmed cases of glyphosate resistant weed populations in Europe. The first reported European case dates back to 2004 and involved four populations of Conyza bonariensis found in southern Spanish olive groves. The glyphosate rates required to control resistant populations were 7 to 10 times higher than those needed to control the susceptible populations. In 2006 a resistant population of C. canadensis was reported in southern Spain while another one was claimed in the Czech Republic in 2007. The resistance in Czech Conyza is currently still under investigation. Recently glyphosate-resistant Lolium rigidum was found in French vineyards (2005 and 2007) and in Spanish citrus groves (2006), while resistant L. multiflorum was identified in Spanish olive groves (2006). New cases of resistant Lolium spp. are reported from Italian vineyards and olive groves. In all these cases Lolium plants were not controlled at recommended glyphosate field rates. Although glyphosate resistant weed populations in Europe are only a few, the sole reliance on glyphosate for weed control especially in perennial crops bears the risk of selecting more resistant populations. Resistance management should be based on principles of Good Agricultural Practices and Integrated Weed Management: - use the right rate at the right time; - apply glyphosate when the plants are more susceptible and the environmental conditions are favourable for its uptake; - integrate herbicides with different mode of action (e.g. a selective or residual herbicide) and mechanical weed control in the weed control program. The new EU legislation on plant protection products is likely to decrease the number of active ingredients and herbicidal mode of actions available for weed control and therefore introduces new challenges for managing weed resistance.

The aim of this study was to analyse the glyphosate resistance mechanisms in Lolium multiflorum and Lolium rigidum. Both these species were collected in Spain, the former in Andalusia in olive grove crops and the latter in citrus plantations in Valencia. These were compared to a susceptible population of both species, which had never been treated with herbicides. Absorption-translocation, contact angle and retention assays were performed. The experiment design used was completely random with six replications. The study was performed as a consequence of data previously obtained for screening and dose-response trials, and which served to confirm the resistance of the resistant biotypes. Regarding the dose-response tests, these were carried out at different growth stages of the plants, with the ED50 values exhibiting an increase as their degree of growth increased. The results obtained in these trials showed that there were no significant differences in L. multiflorum. In the case of L. rigidum, there were significant differences in the foliar penetration tests, with around 20% of the 14C-glyphosate deposited on the resistant biotype being absorbed; differences in the translocation towards the root and in the retention of the glyphosate were also found., La finalidad de este estudio es analizar los mecanismos de resistencia a glifosato en Lolium multiflorum y Lolium rigidum, ambas especies colectadas en España, la primera en la región de Andalucía en cultivos de olivar y la segunda en plantaciones de cítricos en la región de Valencia. Fueron comparadas con una población sensible de ambas especies, que nunca se han tratado con herbicidas. Se han realizado ensayos de absorcióntranslocación, ángulo de contacto y retención. El diseño experimental usado fue completamente al azar con seis repeticiones. El estudio se realizó en consecuencia a los datos obtenidos anteriormente para los ensayos de screening y dosis-respuesta, y que sirvieron para confirmar la resistencia de los biotipos resistentes. En el caso de los ensayos de dosis-respuesta, estos se realizaron en diferentes estadios de crecimiento de las plantas aumentando los valores de ED50 al aumentar el grado de desarrollo de las mismas. Los resultados obtenidos en los estudios del presente trabajo muestran que no existen diferencias significativas en L. multiflorum para los ensayos realizados. En el caso de L. rigidum existen diferencias significativas en los ensayos de penetración foliar, absorbiendo alrededor del 20 % del 14C-glifosato depositado en el biotipo resistente; además se han encontrado diferencias en la translocación hacia la raíz y retención del formulado.

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