HRAC GROUP 2 (LEGACY B) RESISTANT AFRICAN MUSTARD
(Brassica tournefortii)

Inhibition of Acetolactate Synthase HRAC Group 2 (Legacy B)

Australia, South Australia

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INTRODUCTION AFRICAN MUSTARD African Mustard (Brassica tournefortii) is a dicot weed in the Brassicaceae family.  In South Australia this weed first evolved resistance to Group 2 (Legacy B) herbicides in 1996 and infests Cereals.   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 chlorsulfuron, imazamox, imazapyr, and sulfometuron-methyl 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 Jan 22, 2014 ) Common Name African Mustard Species Brassica tournefortii Group Inhibition of Acetolactate Synthase HRAC Group 2 (Legacy B) Herbicides chlorsulfuron, imazamox, imazapyr, and sulfometuron-methyl Location Australia, South Australia Year 1996 Situation(s) Cereals Contributors - (Alphabetically) Christopher Preston  Edit this Case  |  Add New Case of Resistance  |  Add Note

ACADEMIC ASPECTS Confirmation Tests Greenhouse, and Laboratory trials comparing a known susceptible African Mustard biotype with this African Mustard 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 African Mustard 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 Studies on the mechanism of resistance of Group 2 (Legacy B) resistant African Mustard from South Australia indicate that resistance is due to an altered target site.  There may be a note below or an article discussing the mechanism of resistance in the Fact Sheets and Other Literature   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 African Mustard from South Australia please update the database.   Edit Case  |  Add Note  |  Add Article  |  Add New Case  |  Help

CONTRIBUTING WEED SCIENTISTS CHRISTOPHER PRESTON University Of Adelaide - Waite Campus Crc For Australian Weed Management And School Of Agriculture Box 2146 Adelaide, 5064, South Australia Australia Email Christopher Preston

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

Herbicide Resistant African Mustard Globally (Brassica tournefortii) Herbicide Resistant African Mustard Globally (Brassica tournefortii) Drag a column header and drop it here to group by that column Herbicide Resistant African Mustard Globally (Brassica tournefortii) # Country Country StateName FirstYear Situation Active Ingredients CountryID Site of Action WeedID Species CommonName ResistID 1 Australia (Western Australia) Australia Western Australia 1992 Wheat chlorsulfuron 1 Inhibition of Acetolactate Synthase ( HRAC Group 2 (Legacy B) 37 Brassica tournefortii African Mustard 12 2 Australia (South Australia) Australia South Australia 1996 Cereals chlorsulfuron, imazamox, imazapyr, and sulfometuron-methyl 1 Inhibition of Acetolactate Synthase ( HRAC Group 2 (Legacy B) 37 Brassica tournefortii African Mustard 5202

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Boutsalis, P. ; Karotam, J. ; Powles, S. B.. 1999. Molecular basis of resistance to acetolactate synthase-inhibiting herbicides in Sisymbrium orientale and Brassica tournefortii. Pesticide Science 55 : 507 - 516.

Three Australian Sisymbrium orientale and one Brassica tournefortii biotypes are resistant to acetolactate synthase (ALS)-inhibiting herbicides due to their possession of an ALS enzyme with decreased sensitivity to these herbicides. Enzyme kinetic studies revealed no interbiotypic differences within species in K_m (pyruvate) (the substrate concentration at which the reaction rate is half maximal) but a greater V_max (the rate when the enzyme is fully saturated with substrate) for two of the resistant S. orientale biotypes over susceptible levels. F₁ hybrids from reciprocal crosses between resistant and susceptible biotypes of S. orientale showed an intermediate response to chlorsulfuron compared to the parental plants. ALS herbicide resistance in S. orientale segregated in a 3:1 (resistant:susceptible) ratio in F₂ plants with a single rate of chlorsulfuron, indicating that resistance is inherited as a single, incompletely dominant nuclear gene. Two regions of the ALS structural gene known to vary in ALS-resistant biotypes were amplified and sequenced. Resistant S. orientale biotypes NS01 and SS03 contained a single nucleotide substitution in Domain B, predicting a Trp (in susceptible) to Leu (in resistant) amino acid change. Two adjacent nucleotide substitutions (CCT to ATT) predicting a Pro (in susceptible) to Ile (in resistant) change in the primary amino acid sequence were identified in Domain A of resistant S. orientale biotype SS01. Likewise, a single nucleotide substitution at the same site in the resistant B. tournefortii biotype predicts a Pro (in susceptible) to Ala (in resistant) substitution. No other interbiotypic nucleotide differences predicted amino acid changes in the sequenced regions, suggesting that the amino acid substitutions reported above are responsible for resistance to ALS-inhibiting herbicides in the respective biotypes..

Rieger, M. A. ; Preston, C. ; Powles, S. B.. 1999. Risks of gene flow from transgenic herbicide-resistant canola (Brassica napus) to weedy relatives in southern Australian cropping systems. Australian Journal of Agricultural Research 50 : 115 - 128.

It is likely that transgenic canola [rape] expressing genes encoding resistance to glyphosate and glufosinate ammonium will be introduced into the Australian cropping system in the next few years. One risk associated with the introduction of such cultivars is the release of herbicide resistance genes into weedy relatives of canola. This review examines the currently available experimental information regarding the possibility of gene flow from canola to weedy relatives. Three species are identified as having the potential to outcross with canola, Brassica juncea, B. rapa [B. campestris] and Raphanus raphanistrum. The first two of these species are not yet widespread weeds of the southern Australian cropping zone. In contrast, R. raphanistrum is already a major weed in Australia with existing resistance to acetolactate synthase (ALS)-inhibiting herbicides. Information is urgently needed to determine whether successful hybrids between B. napus and R. raphanistrum can be produced under Australian conditions. Major deficiencies in the existing information are identified in relation to some other important weed species within the southern Australian cropping zone. Further studies are required to determine the outcrossing potential of canola to B. tournefortii, Diplotaxis tenuifolia, Sisymbrium officinale and S. orientale if transgenic canola is to be safely and responsibly introduced into Australia..

Adkins, S. W. ; Wills, D. ; Boersma, M. ; Walker, S. R. ; Robinson, G. ; McLeod, R. J. ; Einam, J. P.. 1997. Weeds resistant to chlorsulfuron and atrazine from the north-east grain region of Australia. Weed Research (Oxford) 37 : 343 - 349.

Studies showed that at least 6 weeds found in the grain region of north-east Australia evolved resistance to one or other of the herbicides chlorsulfuron and atrazine. Two collections of Rapistrum rugosum, three of Sisymbrium orientale, five of Sonchus oleraceus, one of Fallopia convolvulus and one of Sisymbrium thellungii were resistant to the recommended rate of chlorsulfuron (15 g a.i. ha^-1). Resistance to chlorsulfuron was not discovered in three collections of Sisymbrium irio, two of Brassica tournefortii, three of Emex australis and 11 of Phalaris paradoxa. Two collections of Urochloa panicoides were resistant, and three collections possibly resistant, to the recommended rate of atrazine (1.8 kg a.i. ha^-1). Resistance to atrazine was not found in 12 collections of Hibiscus trionum, nine of Salvia reflexa, two of Parthenium hysterophorus, two of Amaranthus viridis and 14 of Echinochloa colona. The resistance status of four weeds (R. rugosum, F. convolvulus, S. thellungii and U. panicoides) was confirmed using a multiple concentration-response screen and is the first report of resistance for these species. Herbicide usage records showed that resistance has developed after 3-10 years of selection with chlorsulfuron, and 2-15 years of selection with atrazine, with no correlation between the frequency of use and the degree of resistance for any of the species where eight or more collections were made..

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