Multiple resistant Arctotheca calendula from Australia, Western Australia

INTERNATIONAL HERBICIDE-RESISTANT WEED DATABASE

MULTIPLE RESISTANT CAPEWEED
(Arctotheca calendula)

Multiple Resistance: 3 Sites of Action
Inhibition of Acetolactate Synthase HRAC Group 2 (Legacy B)
Phytoene Desaturase inhibitorsHRAC Group 12 (Legacy F1)
Inhibition of Enolpyruvyl Shikimate Phosphate Synthase HRAC Group 9 (Legacy G)

Australia, Western Australia

INTRODUCTION		CAPEWEED
Capeweed (Arctotheca calendula) is a dicot weed in the Asteraceae family. In Western Australia this weed first evolved multiple resistance (to 3 herbicide sites of action) in 2020 and infests Wheat. Multiple resistance has evolved to herbicides in the Groups 2 (Legacy B), Phytoene Desaturase inhibitors HRAC Group 12 (Legacy F1), and Inhibition of Enolpyruvyl Shikimate Phosphate Synthase HRAC Group 9 (Legacy G). These particular biotypes are known to have resistance to diflufenican, glyphosate, and metosulam and they may be cross-resistant to other herbicides in the Groups 2 (Legacy B), Phytoene Desaturase inhibitors HRAC Group 12 (Legacy F1), and Inhibition of Enolpyruvyl Shikimate Phosphate Synthase HRAC Group 9 (Legacy G). 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 26, 2021 )
Common Name	Capeweed
Species	Arctotheca calendula
Group	Inhibition of Acetolactate Synthase HRAC Group 2 (Legacy B) Phytoene Desaturase inhibitors HRAC Group 12 (Legacy F1) Inhibition of Enolpyruvyl Shikimate Phosphate Synthase HRAC Group 9 (Legacy G)
Herbicides	diflufenican, glyphosate, and metosulam
Location	Australia, Western Australia
Year	2020
Situation(s)	Wheat
Contributors - (Alphabetically)	Michael Ashworth, Hugh Beckie, and Heping Han
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NOTES ABOUT THIS BIOTYPE

GENERAL

Pest Management Science 2021. DOI 10.1002/ps.6295

Identification of the first glyphosate-resistant capeweed (Arctotheca calendula) population

Yaseen Khalil,^a* Michael B Ashworth,^aHeping Han,^a Yu Qin,^a Roberto L Rocha,^aBrent Pritchard,^bDavid Cameron^cand Hugh J Beckie^a Abstract

BACKGROUND: Glyphosate is routinely used in Australia to control the Arctotheca species Arctotheca calendula (L.) Levyns (referred hereinafter as capeweed). This study identifies the first global case of field-evolved glyphosate-resistant capeweed, collected from the grainbelt of Western Australia.

RESULTS: In 2020, a capeweed biotype that was collected from Borden in the southern Western Australian grainbelt was confirmed to be glyphosate-resistant (referred hereinafter as Spence population). When compared to the pooled mortality of six field-collected, glyphosate susceptible capeweed populations (S1, S2, S3, S4, S5 and S6), the Spence population was found > 11-fold more resistant to glyphosate than the pooled results of the susceptible populations (S1–S6) at the lethal dose of 50% (LD₅₀) level. The growth of the Spence population was also less affected, requiring > 13-fold more glyphosate to reduce growth than the pooled susceptible populations at the growth reduction of 50% (GR₅₀) level. Sequencing of the plastidic 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) gene indicated no known single gene mutation imparting glyphosate resistance. This study, however, did not investigate any other known mechanisms that impart glyphosate resistance. When screened at the field-applied rate, this Spence population was also found to survive an inhibitor of acetolactate synthase (ALS) (metosulam) and an inhibitor of phytoene desaturase (diflufenican).

CONCLUSIONS: This is the first confirmation of glyphosate resistance evolution in a capeweed population globally. With capeweed resistance already confirmed to photosystem-I inhibiting herbicides (paraquat and diquat), this study emphasizes the importance of using integrated measures that do not depend only on the use of non-selective herbicides for controlling herbicide resistance-prone capeweed populations. © 2021 Society of Chemical Industry

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ACADEMIC ASPECTS

Confirmation Tests

Greenhouse, and Laboratory trials comparing a known susceptible Capeweed biotype with this Capeweed 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, 12, 9 resistant Capeweed 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 multiple resistant Capeweed from Western Australia please update the database.

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CONTRIBUTING WEED SCIENTISTS

MICHAEL ASHWORTH

PhD Student University of Western Australia, School of Botany Australian Herbicide Resistance Initiative University of Western Australia Crawley, 6009, Western Australia Australia Email Michael Ashworth Web : Web Site Link

HUGH BECKIE

Professor of Crop Weed Science...Canadian Expat University of Western Australia Australian Herbicide Resistance Initiative School of Agriculture and Environment 35 Stirling Highway Crawley, 6009, Western Australia Australia Email Hugh Beckie Web : Web Site Link

HEPING HAN

Research associate Australian herbicide resistance initiative University of Aestern Australia Crawly Perth, 6009, Western Australia Australia Email Heping Han Web : Web Site Link

ACKNOWLEDGEMENTS
The Herbicide Resistance Action Committee, The Weed Science Society of America, and weed scientists in Western Australia have been instrumental in providing you this information. Particular thanks is given to Michael Ashworth, Hugh Beckie, and Heping Han for providing detailed information.

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Herbicide Resistant Capeweed Globally
(Arctotheca calendula)

Country

FirstYear

Situation

Active Ingredients

Site of Action

Australia (Victoria)

1986

Alfalfa

diquat

PS I Electron Diversion ( HRAC Group 22 (Legacy D)

Australia (South Australia)

2015

Fallow

2,4-D

Auxin Mimics ( HRAC Group 4 (Legacy O)

Australia (Western Australia)

2020

Wheat

diflufenican, glyphosate, and metosulam

Multiple Resistance: 3 Sites of Action
Inhibition of Acetolactate Synthase ( HRAC Group 2 (Legacy B)
Phytoene Desaturase inhibitors ( HRAC Group 12 (Legacy F1)
Inhibition of Enolpyruvyl Shikimate Phosphate Synthase ( HRAC Group 9 (Legacy G)

Literature about Similar Cases

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Wells, G. S.. 2008. Florasulam+isoxaben for management of herbicide resistant wild radish in Western Australia. : 336 - 338.

In 2007 Dow AgroSciences registered florasulam+isoxaben as X-Pand^TM Herbicide (40 g florasulam+610 g isoxaben kg^-1) for broadleaf weed control in winter cereals. This combination of active ingredients gives good control of key weeds like wild radish (Raphanus raphanistrum L.), capeweed (Arctotheca calendula (L.) Levyns), doublegee (Emex australis Steinh.) and volunteer legumes, either applied alone or tankmixed, with good cereal selectivity. However, there will be significant plantback periods for some crops. This paper summarises research trials conducted to confirm cereal selectivity, wild radish control and comments on crop rotation flexibility for this product..

Soar, C. J. ; Preston, C. ; Karotam, J. ; Powles, S. B.. 2004. Polyamines can inhibit paraquat toxicity and translocation in the broadleaf weed Arctotheca calendula. Pesticide Biochemistry and Physiology 80 : 94 - 105.

Reduced paraquat transport from the site of application to the site of action in the chloroplast seems a likely mechanism for paraquat resistance in several weed species including Arctotheca calendula. Recently, it has been shown that paraquat translocation in A. calendula is correlated with paraquat-induced injury and is reduced in paraquat-resistant A. calendula. Studies with leaf slices have shown that some polyamines when applied concomitantly with paraquat can reduce the toxic effects of paraquat. This study examined the effects of three polyamines, putrescine, cadaverine, and spermidine, on paraquat translocation to examine the possibility that paraquat translocation in susceptible plants would be reduced in the presence of polyamines due to competition of the polyamines with cellular paraquat uptake. Two polyamines, spermidine and cadaverine were effective in reducing paraquat translocation in susceptible A. calendula inducing these plants to perform more like resistant A. calendula in terms of translocation. Quantification of the polyamine contents of resistant and susceptible A. calendula showed that resistant plants have higher constitutive spermidine levels than susceptible plants, which infers a possible role of either polyamines or a polyamine transporter in paraquat resistance..

Soar, C. J. ; Karotam, J. ; Preston, C. ; Powles, S. B.. 2003. Reduced paraquat translocation in paraquat resistant Arctotheca calendula (L.) Levyns is a consequence of the primary resistance mechanism, not the cause. Pesticide Biochemistry and Physiology 76 : 91 - 98.

Resistance to paraquat has been studied in detail in many weed species for more than a decade, with the precise mechanism of resistance still unclear. Several studies have indicated that reduced movement of the herbicide to the site of action in the chloroplast is at least partly responsible for endowing resistance. Although paraquat translocation studies have been performed in the past it has been rare for these studies to have been conducted on whole plants in the light, despite early observations which clearly showed that paraquat translocation is minimal unless treated plants are exposed to light. This study has addressed this issue in Arctotheca calendula by tracing the movement of ¹⁴C-paraquat in resistant and susceptible plants in both the dark and light. Differences in paraquat translocation between the resistant and susceptible biotypes of A. calendula were only observed when treated plants were exposed to light. It was observed that paraquat translocation was significantly reduced in the resistant compared to the susceptible biotype when plants were exposed to light but not in the dark. It is postulated that paraquat translocation is dependent on light mediated damage. As paraquat-induced damage is less severe in paraquat resistant plants, overall paraquat translocation is reduced in the resistant biotype..

Lemerle, D. ; Blackshaw, R. E. ; Smith, A. B. ; Potter, T. D. ; Marcroft, S. J.. 2001. Comparative survey of weeds surviving in triazine-tolerant and conventional canola crops in south-eastern Australia. Plant Protection Quarterly 16 : 37 - 40.

Many farmers grow triazine-tolerant (TT) canola [rape] to enable control of difficult weeds and to allow early sowing. The efficacy of triazine herbicides in canola influences the development of future weed problems. A survey was conducted to determine the incidence and abundance of weeds surviving in TT and conventional canola crops across south-eastern Australia. Fifty-five canola paddocks (27% TT and 73% conventional) were selected at random in August/September 1998 when most weed management practices were already completed by farmers. Seventy-three weed species were identified, some at densities of up to several hundred plants m^-2. This has serious implications for weed seed bank replenishment and the perpetuation of weed populations requiring control in future crops. The most widespread grass species at more than 30% of sites were Lolium rigidum, Avena spp., and Vulpia spp., while the main broadleaf weeds were Arctotheca calendula, Polygonum aviculare, and Fumaria spp. Some weeds were more prevalent in conventional canola (e.g. Fumaria spp., Arctotheca calendula, Capsella bursa-pastoris and Papaver somniferum) while others were more common in TT (e.g. Anagallis arvensis, Raphanus raphanistrum, Lepidium africanum and Conringia orientalis). These results suggest that widespread adoption of TT canola will affect weed population dynamics in canola thereby leading to new weed problems in canola..

Preston, C. ; Balachandran, S. ; Powles, S. B.. 1994. Investigations of mechanisms of resistance to bipyridyl herbicides in Arctotheca calendula (L.) Levyns. Plant, Cell and Environment 17 : 1113 - 1123.

The mechanism of resistance to diquat and paraquat was investigated in a bipyridyl-herbicide-resistant biotype of Arctotheca calendula. No differences were observed in the interactions of these herbicides with PSI, the active site, in thylakoids isolated from resistant and susceptible biotypes. Likewise, absorption of herbicide through the cuticle and gross translocation were identical in plants of the two biotypes. Foliar application of either 25 g/ha diquat or 200 g paraquat rapidly inhibited CO₂-dependent O₂ evolution of leaf segments of the susceptible biotype. O₂ evolution of leaf segments of the resistant biotype was less affected by these treatments. Fluorescence imaging was used to observe visually, as fluorescence quenching, the penetration of herbicide to the active site. These experiments demonstrated that diquat appears at the active site more slowly in the resistant biotype compared to the susceptible biotype. HCO₃-dependent O₂ evolution of thin leaf slices was less inhibited by diquat in the resistant biotype than in the susceptible biotype. It was concluded that the mechanism of resistance to the bipyridyl herbicides in this biotype of A. calendula is not a result of changes at the active site, decreased herbicide absorption or decreased translocation, but appears to be due to reduced herbicide penetration to the active site..

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