Staff Update

4th Year Student Projects

Stephen Powles on study leave in France

WAHRI Journal articles

WAHRI Conference articles 

Crop seed stocks conceal herbicide resistant weed seed

Contamination of crop seed can have an unwanted effect on the crop and also introduce foreign weed seeds and herbicide resistant weeds.  Recent research suggests that seed cleaning operations are only partially effective in removing weed seed, resulting in increased weed control costs and long term yield losses.

In WA, herbicide resistance is widespread in annual ryegrass and wild radish populations.  WAHRI Research Officer, Mechelle Owen undertook a project to determine the extent of weed seed contamination in crop seed sown by farmers in the WA grain belt.

A total of 183 grain samples were provided from 78 farms across the WA grainbelt.  In total, 74% of collected grain samples had some level of weed seed contamination with annual ryegrass the most frequent contaminant followed by wild radish. Many of the weed seeds found in the crop seed were also resistant to commonly used herbicides.

Reducing the weed seed burden is dependent on planting clean crop seed; controlling weeds during the cropping phase (harvesting a 'weed free' paddock) and preventing weed seed contamination from other sources.  Seed cleaning will not totally eradicate all weed seed, especially the prevalent WA crop weeds, annual ryegrass and wild radish. However, seed cleaning will help to reduce the costs associated with planting herbicide resistant weed seeds into cropping paddocks.

This paper was presented at 2009 Perth Crop Updates.  For more information contact Mechelle Owen. 

Glyphosate resistance

Glyphosate continues to be the world’s most important and widely used herbicide.  WAHRI research is demonstrating that it is essential for glyphosate to be used at full label rates and that rate cutting should not occur.

Recent studies on cross-pollinated annual ryegrass have shown that after only three cycles of glyphosate selection, the progeny of a glyphosate-susceptible annual ryegrass population has shifted towards being resistant.  It is already widely known that major genes confer glyphosate resistance however the impact of minor resistance genes on the plant's ability to survive sub-lethal herbicide doses may also be contributing to the evolution of resistance in weed populations.

WAHRI staff member, Dr Roberto Busi experimented further to ascertain the potential for sub-lethal glyphosate doses to select for resistance.  A shift towards glyphosate resistance (33% plant survival at the recommended glyphosate rate) was evident after three selection cycles at sub-lethal glyphosate doses.  This suggests minor gene traits are contributing to glyphosate resistance in the selected progeny.

For more information contact Dr Roberto Busi  

Pollen mediated gene flow in Roundup Ready canola

A Grains Research and Development Corporation (GRDC) funded research project, 'Gene flow in transgenic Roundup Ready (RR) Canola', will run alongside 20 genetically modified (GM) canola trials, covering 854 hectares, in WA this season.

The project started in eastern Australia in 2008 and will help to address concerns about the potential for gene flow from genetically modified (GM) Canola to nearby canola crops.   Gene flow studies have already been completed in imidazolinone tolerant or Clearfield canola.  With the commercial release of GM RR canola, field studies on pollen flow and the impacts on weed populations will be measurable in a GM situation.

Given the weight of public concern regarding contamination from genetically modified crops, this project will carry out an extensive investigation into the impact on surrounding crops during the upcoming growing season.  It is expected, that although canola is mostly self-pollinated, cross pollination via insects and/or wind will occur.
 
For more information contact Dr Roberto Busi and Prof Stephen Powles

Pyroxasulfone

In a world first, A WAHRI collaboration with Kumiai Chemical Industry Co (Japan) will address the potential for resistance development to a new herbicide prior to its release.

An ARC Linkage grant has been established to provide funds to study herbicide resistance in annual ryegrass to the herbicide pyroxasulfone, a product due to be released by Kumiai in 2011. 

Pyroxasulfone will be used in Australia for pre-emergent control of annual ryegrass and other weeds in wheat crops.   

WAHRI researchers Roberto Busi and Todd Gaines, under the supervision of Professor Stephen Powles, are evaluating whether resistance will evolve under a sub-lethal dose strategy, and measure the frequency of resistance within annual ryegrass populations subjected to very high pyroxasulfone rates. 

Research examining recurrent selection under sub-lethal rates has been conducted for three generations and the selected populations have been evaluated for resistance to pyroxasulfone and cross-resistance to other common herbicides. 

A field trial at UWA’s Shenton Park is designed to evaluate resistance to high rates of pyroxasulfone.  The WAHRI-Kumiai study will determine whether the basis of resistance in annual ryegrass is due to increased herbicide metabolism, and whether differences in herbicide metabolism rates provide the selectivity between grass weeds and crop species.

The major objective of the project is to provide guidance for minimising the likelihood of pyroxasulfone resistance evolving in annual ryegrass in Australia.

For more information contact Dr Todd Gaines.

Evolution of herbicide resistance at low rates of herbicide

The effect of low rates of herbicide application in the evolution of herbicide resistance in L.rigidum was recently confirmed by PhD student Sudheesh Manalil.  In this study, two consecutive cycles of selection were carried out at sub-lethal rates of diclofop-methyl in a herbicide susceptible L. rigidum population, in both field and controlled conditions.  The dose response profile revealed a substantial level of diclofop-methyl resistance in the twice-selected Lolium lines both in the field and pot study.

Cross-resistance profiling of both the twice-selected generations from the field and pot studies revealed a substantial level of resistance to two other ACCase herbicides (haloxyfop-R-methyl and fluazifop-P-butyl) and to the dissimilar ALS herbicides chlorsulfuron and imazethapyr.  The study indicates the potential of low rate in the rapid evolution of herbicide resistance and cross-resistance in L. rigidum. 

In another study, a susceptible L.rigidum population was shifted to greater susceptibility by recurrently selecting the susceptible individuals with low rates of diclofop-methyl.  L. rigidum were cloned (divided into two identical portions) at the six-leaf stage. One series of cloned plants was treated with a very low diclofop-methyl dose (94 g ha-1). The untreated clone of an individual observed to be highly herbicide-susceptible was selected and bulk-crossed to obtain the selected seed progeny. The next cycle of selection was conducted by reducing the rate further (47 g diclofop-methyl ha-1). 

Dose-response studies with selected lines indicate greater susceptibility with selection. The cross-resistance profiling of the twice-selected line revealed an increased susceptibility to two other ACCase herbicides (haloxyfop and sethoxydim) and to the different mode of action ALS herbicide chlorsulfuron. The results indicated that minor resistance traits were present in a herbicide-susceptible ryegrass population and may be removed from a susceptible population of ryegrass, further increasing the level of susceptibility.

Simulation modelling was used to understand the genetic basis of the selected herbicide resistance traits, which lead to the evolution of herbicide resistance at low rates. In addition, the data generated in the field experiment was used to validate the simulation model to predict the impact of different herbicide rates (low to high) in the evolution of herbicide resistance. Simulated dose response of the evolved susceptible lines provided better understanding of the minor resistance traits present in the L.rigidum population.

For more information contact Sudheesh Manalil

Herbicide resistance in wild oats:  Confirmation of resistance to several Group A herbicides

Wild oat resistance to Group A herbicides was first recorded in 1985, since then many more cases of resistance have been documented with resistance to Group A FOP herbicides the most common.  With increasing reliance on rotation of herbicides from other chemical families, resistance to DIM and DEN herbicides has been observed.  This study aims to provide a summary on the resistance status of four previously selected wild oats populations to the FOP, DIM and DEN herbicides.

The study findings confirmed cross-resistance to all five group A herbicides being used, with the effectiveness of FOP (Hoegrass and Wildcat) being considerably lower than for DIM  (Select and Sertin) and DEN (Axial) herbicides.  Dose response studies reveal a wide variation in level of resistance between the herbicides used, with Hoegrass and Wildcat having very high plant survival at all rates applied.  At the recommended label rate (0.35L/ha), 100% survival was observed from three of the populations whilst almost 95% survival was observed from the remaining population.  At the highest rate (2.8 L/ha), a range of 62-83% survival was recorded for the same three populations with the other population reduced to 20% survival.

With application of the DIM herbicide (Sertin), all populations were shown to be resistant at the label rate (1 L/ha) with survival ranging from 74 to 100%.  However, at the highest rate (8 L/ha), two populations were classed as resistant (average 35% survival ) whilst the other two populations were 100% susceptible.

With DEN herbicide ‘Axial’, only one population was effectively controlled by the herbicide at label rate (0.2 L/ha) with only 16% survival.  The remaining three populations recorded between 50 and 82% survival.  At the highest rate (1.6L/ha) two populations were successfully controlled (no survivors), whilst two populations had between 13 and 37% survival.

The herbicide ‘Select’ was the most effective of the herbicides used in controlling the wild oats populations with the label rate (0.25 L/ha)

For more information contact Saiful Hamdani

Staff Update

Recent staff changes at the WA Herbicide Resistance Initiative (WAHRI) have seen Drs Michael Walsh and David Minkey take up positions with the Birchip Cropping Group and WA No-till Farmers Association (WANTFA) respectively.

Dr Michael Walsh moved to a collaborative position with the Victorian based Birchip Cropping Group (BCG) and The University of Melbourne as Senior Research Scientist in February 2009.  He will focus on a project investigating weeds in Victorian cropping systems.  Michael and his family are now based in Birchip. 

Michael Walsh made many important contributions to WA cropping during his 10 years in WAHRI and will be missed.  However, he is staying in close contact with the WAHRI team and will continue to contribute to Australian cropping.

Dr David Minkey was appointed Executive Officer of WANTFA in February 2009 and remains in close proximity as the WANTFA office is based at The University of WA (UWA). David has had a lengthy career in DAFWA after which he completed his PhD at WAHRI and continued employment with WAHRI.  His appointment with WANTFA will help ensure the already close relations between WAHRI and WANTFA.

New Staff

Dr Todd Gaines joined WAHRI in February this year as a Research Associate.  Todd hails from Colorado in the US and is working on an ARC Linkage project on resistance to Pyroxasulfone (Sakura) before it is commercialised in Australia.  Kumiai, Japan is a collaborator on this project and Sakura is under development in Australia by Bayer Crop Science.

For his PhD Todd worked on glyphosate resistance evolution in Amaranthus in the US and his outstanding research was recently recognised by the Weed Science Society of America’s (WSSA) 2008 Outstanding Graduate Student award. Todd also has a Masters degree for his work on pollen-mediated gene flow in wheat using herbicide resistance as a marker. 

Dr Rowena Long joined WAHRI in 2008 as a Research Associate funded by an ARC - Kings Park Linkage grant to investigate the broad-acre weed potential for karrikinolide. 

Karrikinolide is a chemical that was originally identified from smoke that is capable of triggering seeds to germinate. Rowena is investigating the potential of karrikinolide for promoting synchronous germination of weeds by specifically targeting the dormant weed seed bank.  Rowena hopes this highly potent, naturally occurring stimulant will prove its worth in years to come.

For further information contact Dr Rowena Long 

Ms Lisa Mayer was appointed WAHRI Administrative Officer in February and is responsible for the management of WAHRI accounts and communication activities.  Lisa previously worked with the Grower Group Alliance and Curtin University, in extension/communication roles.

4th Year Student Projects

Ms Joanne Shaddick is working with Dr Roberto Busi and Prof Powles on a project examining  glyphosate resistance in genetically-modified (RoundUp Ready) versus triazine tolerant canola.  This project will answer key agronomic questions about the potential benefits or constraints in cultivation of GM glyphosa-resistant canola versus conventional triazine tolerant varieties.  Preliminary work will be conducted to evaluate pollen-mediated gene flow in GM glyphosate-resistant canola under agronomic conditions.  The experiments will provide useful data to identify potential hybrid plants due to cross-pollination between GM plants and conventional varieties.  This is timely research with 2009 seeing 1000 hectares of Roundup Ready canola sown in the WA wheatbelt.

For further information contact Dr Roberto Busi 

Ms Karrie Stratford successfully completed her fourth year project investigating ways to improve herbicide efficiency through synergistic herbicide use on wild radish populations. Following up on earlier work in WAHRI, Karrie established that the HPPD herbicide mesotrione has definite synergism with atrazine.  Synergism is evident in the new Bayer herbicide Velocity which combines the HPPD herbicide pyrasulfatole with bromoxynil for a synergistic effect.

For further information contact Prof Stephen Powles   

Mr Robert Alderman completed his fourth year project on karrikinolide as a germination stimulant for ryegrass, wild turnip, wild oat and wild radish.  He showed that karrikinolide does not appear to stimulate germination of ryegrass but does stimulate wild radish seed germination.  This work is being thoroughly investigated by Dr Rowena Long

Karrikinolide is known to stimulate germination of some significant agricultural weed species at maturity (November to December). With many annual winter weeds, physiological dormancy is alleviated during summer and autumn, altering germination characteristics of seeds.  Robert investigated the response of field stored seeds from maturity until winter in both the field and the greenhouse and found that karrikinolide is an effective germination stimulant of wild turnip and wild radish. Ryegrass requires further investigation, as does wild oat, to determine responses in field populations.

For further information contact Dr Rowena Long                

Stephen Powles on study leave in France

WAHRI Director, Stephen Powles has been granted study leave from UWA to work for three months at the French National Agronomy Research Institute (INRA) in Dijon.  During this period he aims to complete a review on the fitness of herbicide resistant plants as well as a major review on herbicide resistance mechanisms.  

Steve will also resume collaboration with his colleagues at INRA, herbicide resistance experts Drs Xavier Reboud , Christophe Delye and Henri Darmency.  Powles states that “while it is quite hard for me to be away from my colleagues in WAHRI it is just great to have the opportunity to work with my French colleagues in Dijon and enjoy France”.