<b>HRAC Group 2</b> <font size='2'> (Legacy B) </font> resistant Rottboellia cochinchinensis (=R. exaltata) from Venezuela

INTERNATIONAL HERBICIDE-RESISTANT WEED DATABASE

HRAC GROUP 2 (LEGACY B) RESISTANT ITCHGRASS
(Rottboellia cochinchinensis (=R. exaltata))

Inhibition of Acetolactate Synthase HRAC Group 2 (Legacy B)

Venezuela, Portuguesa

INTRODUCTION		ITCHGRASS
Itchgrass (Rottboellia cochinchinensis (=R. exaltata)) is a monocot weed in the Poaceae family. In Venezuela this weed first evolved resistance to Group 2 (Legacy B) herbicides in 2004 and infests Corn (maize). Group 2 (Legacy B) herbicides are known as Inhibition of Acetolactate Synthase (Inhibition of Acetolactate Synthase ). Research has shown that these particular biotypes are resistant to foramsulfuron, iodosulfuron-methyl-Na, and nicosulfuron and they may be cross-resistant to other Group 2 (Legacy B) herbicides. The 'Group' letters/numbers that you see throughout this web site refer to the classification of herbicides by their site of action. To see a full list of herbicides and HRAC herbicide classifications click here.

QUIK STATS (last updated Feb 24, 2015 )
Common Name	Itchgrass
Species	Rottboellia cochinchinensis (=R. exaltata)
Group	Inhibition of Acetolactate Synthase HRAC Group 2 (Legacy B)
Herbicides	foramsulfuron, iodosulfuron-methyl-Na, and nicosulfuron
Location	Venezuela, Portuguesa
Year	2004
Situation(s)	Corn (maize)
Contributors - (Alphabetically)	Aida Ortiz
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ACADEMIC ASPECTS

Confirmation Tests

Greenhouse trials comparing a known susceptible Itchgrass biotype with this Itchgrass biotype have been used to confirm resistance. For further information on the tests conducted please contact the local weed scientists that provided this information.

Genetics

Genetic studies on HRAC Group 2 resistant Itchgrass have not been reported to the site. There may be a note below or an article discussing the genetics of this biotype in the Fact Sheets and Other Literature

Mechanism of Resistance

The mechanism of resistance for this biotype is either unknown or has not been entered in the database. If you know anything about the mechanism of resistance for this biotype then please update the database.

Relative Fitness

There is no record of differences in fitness or competitiveness of these resistant biotypes when compared to that of normal susceptible biotypes. If you have any information pertaining to the fitness of Group 2 (Legacy B) resistant Itchgrass from Venezuela please update the database.

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CONTRIBUTING WEED SCIENTISTS

AIDA ORTIZ

Professor Universidad Central De Venezuela Agronomia Avenida Universidad. Campus Maracay Maracay, 2101, Aragua Venezuela Email Aida Ortiz Web : Web Site Link

ACKNOWLEDGEMENTS
The Herbicide Resistance Action Committee, The Weed Science Society of America, and weed scientists in Venezuela have been instrumental in providing you this information. Particular thanks is given to Aida Ortiz for providing detailed information.

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Herbicide Resistant Itchgrass Globally
(Rottboellia cochinchinensis (=R. exaltata))

Country

FirstYear

Situation

Active Ingredients

Site of Action

United States (Louisiana)

1997

Soybean

fluazifop-butyl

Inhibition of Acetyl CoA Carboxylase ( HRAC Group 1 (Legacy A)

Venezuela

2004

Corn (maize)

foramsulfuron, iodosulfuron-methyl-Na, and nicosulfuron

Inhibition of Acetolactate Synthase ( HRAC Group 2 (Legacy B)

Literature about Similar Cases

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Gámez, A. ; Zambrano, C. ; Ramis, C.. 2013. Metabolic and enzymatic characterization of nicosulfuron resistance in biotypes of Rottboellia cochinchinensis (Lour.) WD Clayton. Bioagro 25 : 3 - 10.

Rottboellia cochinchinensis is a major weed and its chemical control is mainly based on the use of the herbicide nicosulfuron; however, there has been a decrease in the effect of the herbicide on the weed which has showed some levels of resistance. In order to perform a metabolic and enzymatic characterization of the resistance of R. cochinchinensis to nicosulfuron, some experiments were conducted to confirm the selected biotype resistance through an analysis of log-logistic regression and determine the resistance index (IR). The study of the resistance nature was done through inhibition tests of the P₄₅₀ monooxygenases complex by the use of malathion, and in vivo enzymatic assay where acetoin accumulation was measured by colorimetry as an indirect measure of the inhibition of ALS. The dose-response bioassay confirmed the resistance (IR=3.87). There was no reduction in fresh biomass of resistant plants treated with malathion compared to the untreated ones, indicating that cytochrome P₄₅₀ monooxygenase isozymes that could be inhibited by malathion were not involved in the degradation of nicosulfuron in this bioassay. With the in vivo enzymatic assay, we demonstrated the insensitivity of the ALS enzyme of the resistant biotype to nicosulfuron, therefore it is concluded that the resistance mechanism of this biotype is in the action site of the herbicide..

Delgado, M. ; Ortiz Domínguez, A. ; Zambrano, C.. 2008. Populations of Rottboellia cochinchinensis (Lour.) W.D. Clayton cross resistance to foramsulfuron+iodosulfuron. Agronomía Tropical (Maracay) 58 : 175 - 180.

Itchgrass (R. cochinchinensis) is one of the most noxious weed in maize crops in Venezuela. The effect of 6 increasing doses of foramsulfuron+iodosulfuron in 6 nicosulfuron-resistant itchgrass accessions and susceptible population was investigated in a greenhouse. When the plants had 3-4 leaves, they were sprayed with foramsulfuron+iodosulfuron at 0, 18.6, 37.2, 74.4, 148.8 and 297.6 g/ha. The fresh weight of the plants in a log-logistic regression model was analysed, establishing the required dose to inhibit growth at 50% (RC5O) in each biotype and the threshold of resistance index (RI). All the nicosulfuron-resistant populations showed cross-resistance to foramsulfuron+iodosulfuron. Phaller, García, Gómez, Cedeño and Esteger showed the highest values of RI (26.91, 24.64, 23.85, 22.58 and 21.01, respectively), whereas Luchi had the lowest RI (12.6)..

Avila, W. ; Bolaños, A. ; Valverde, B. E.. 2007. Characterization of the cross-resistance mechanism to herbicides inhibiting acetyl coenzyme-A carboxylase in itchgrass (Rottboellia cochinchinensis) biotypes from Bolivia. Crop Protection 26 : 342 - 348.

Whole-plant greenhouse bioassays and absorption, translocation, and metabolism experiments were conducted to investigate the resistance and cross resistance patterns and resistance mechanism of itchgrass (Rottboellia cochinchinensis) biotypes from Bolivia to herbicides that inhibit the enzyme acetyl coenzyme-A carboxylase. Varying levels of resistance to haloxyfop-R-methyl and sethoxydim were found in the biotypes designated as San Pedro and Yapacaní and cross-resistance among graminicides was confirmed. The resistance indices (RI) for haloxyfop-R-methyl based on the GR₅₀ values (herbicide dose required to inhibit growth by 50%) for these biotypes were 33.4 and 44.3, respectively. For the sethoxydim, the RI values were 9.3 and 4.7, respectively. The rate of [¹⁴C]sethoxydim absorption was similar in the resistant and susceptible biotypes at 6, 12, 48 and 96 h after treatment (HAT); there was no significant difference in the amount of [¹⁴C]sethoxydim uptake among biotypes. No differences in the translocation or metabolism of [¹⁴C]sethoxydim were observed between resistant and susceptible biotypes at any interval after application. In in vitro ACCase assays, the concentrations of sethoxydim required to inhibit ACCase activity by 50% (I₅₀) were substantially higher (about 11 times) for the two resistant biotypes compared to the reference biotype, indicating that the resistant itchgrass biotypes have an ACCase that is relatively insensitive to the graminicides. These results suggest that cross resistance in itchgrass biotypes is conferred by a reduced sensitivity of the target enzyme..

Delgado, M. ; Ortiz Domínguez, A. ; Zambrano, C.. 2006. Resistance of Rottboellia cochinchinensis (Lour.) W.D. Clayton to nicosulfuron in maize crops. Agronomía Tropical (Maracay) 56 : 171 - 182.

The control of Itchgrass, R. cochinchinensis, one of the most important weeds of maize in Venezuela is based on nicosulfuron, a postemergent herbicide. However, levels of control have been low, which may suggest resistance of the weed to the herbicide. Resistance of itchgrass, collected in different farms of Portuguese State, to nicosulfuron was evaluated. The resistance of mature seeds of itchgrass collected from 13 farms was compared against the resistance of itchgrass collected in the botanic garden of the Department of Botany of the Faculty of Agronomy where nicosulfuron had never been used. Two experiments were carried out in a greenhouse, in a completely randomized block design with 4 replications, (1) to select resistance to the commercial recommended dose of nicosulfuron (30 i.a. g ha^-1), and (2) to evaluate the resistance of itchgrass to increased doses of nicosulfuron (0, 7.5, 15, 30, 60 and 120 i.a. g ha^-1) with selected plants from experiment 1 where there was low control of itchgrass (<30%) by nicosulfuron. In both experiments nicosulfuron was sprayed using a calibrated CO₂ constant flow sprayer set to 2501/ha, when itchgrass had 3 to 4 leaves. Seedlings were placed in pots with 3 kg of soil. The dose of nicosulfuron which inhibits growth of itchgrass in a 50% (RC50) was estimated through the threshold of resistance index (RI), using the log-logistic model of regression in accordance with Seefeld et al. (1995). We found that 3 of the evaluated populations were susceptible and 11 resistant to nicosulfuron. Resistance index fluctuated between 2.1 and 600.1: Randal (19.7), Phaller (17.4), Esteger (30.7), Gómez (600.1), Luchi (34.4), Cedeño (8.6), Gaester (9.4), Hhaller (2.1), Giacobucci (6.6), Jiménez (39.8) and García (2.5)..

Avila García, W. V. ; Bolaños Espinoza, A. ; Valverde, B. E. ; Segura Miranda, A.. 2004. Resistance of Rottboellia cochinchinensis (Lour) WD Clayton to fluazifop-p-butyl in biotypes from Santa Cruz, Bolivia. : 219 - 225.

The response of Rottboellia cochinchinensis to post-emergent treatment with fluazifop-butyl was evaluated in 5 biotypes from Santa Cruz, Bolivia, during 2003. The biotypes (Aguai, Chane, San Pedro, Yapacani and a control population) were collected from soyabean crops. Fluazifop-butyl was applied at 0, 20, 40, 60, 80, 100, 200 and 400 g a.i./ha. The biotypes San Pedro and Yapacani were highly resistant, Chane had intermediate resistance, while Aguai and the control population were susceptible..

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