ORCID Profile
0000-0002-8403-5029
Current Organisation
University of Adelaide
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Publisher: Wiley
Date: 08-09-2023
DOI: 10.1002/PS.7743
Abstract: Control of prickly lettuce has become increasingly difficult for lentil growers in southern Australia due to widespread resistance to common herbicides, a lack of alternative herbicide options, and prolific production of highly mobile seed. This study aimed to quantify ALS‐inhibiting herbicide resistance in the Mid North (MN) and Yorke Peninsula (YP) of South Australia, characterise the resistance mutations present, and investigate population structure and gene flow in this species. Resistance was identified in all populations tested, with average survival of 92% to chlorsulfuron and 95% to imazamox + imazapyr. Five different amino acid substitutions were identified at Proline‐197 of the ALS gene. There was no significant difference in the LD 50 between plants with these five different substitutions when treated with metsulfuron‐methyl, however, imidazolinone resistance level was higher in plants with a phenylalanine substitution and lower in plants with a serine. Population structure based on 701 SNPs and 271 in iduals provided evidence for both the independent evolution of the same mutation in different populations, as well as frequent short to medium distance dispersal accompanied by occasional long‐distance dispersal events. The overall inbreeding coefficient ( F IS ) was calculated at 0.5174, indicating an intermediate level of outcrossing despite the cross‐pollination experiment showing only low outcrossing. In the structure analyses, most in iduals from YP were assigned to a single cluster, whereas most in iduals from MN were assigned 50% to each of two clusters, indicating some genetic differences between these two regions, but also evidence for dispersal between them. Use of imidazolinone herbicides has selected for mutations conferring higher levels of resistance, such as the Pro‐197‐Phe mutation, and resulted in further spread of resistance in this species. This article is protected by copyright. All rights reserved.
Publisher: Wiley
Date: 25-04-2023
DOI: 10.1002/PS.7498
Abstract: Annual sowthistle is a weed that is difficult to control in lentil crops in southern Australia due to a lack of herbicide options, widespread herbicide resistance and prolific production of highly mobile seed. This study investigates herbicide resistance in annual sowthistle in the Mid‐North (MN) and Yorke Peninsula (YP) regions of South Australia, identifies and characterizes the mechanisms of acetolactate‐synthase (ALS)‐inhibitor resistance in this hidiploid species, and combines this with analyses of population structure and gene flow. ALS‐inhibitor‐resistant annual sowthistle is widespread across the YP and MN of South Australia and is associated with a variety of Proline‐197 mutations of the ALS gene, including leucine, alanine, arginine, serine, threonine and histidine. These mutations were found in different combinations on either of the two copies of the ALS gene. An additional 200 tissue s les were collected from across a single field on the YP and the ALS gene was sequenced for all these in iduals. Different ALS‐inhibitor resistance profiles were evident between mutation combinations and within mutation combinations, possibly mediated by differing subgenome assortment of the mutations, or altered gene experession of the two ALS homeologs. Population genetics analysis showed evidence of long‐distance dispersal, resulting in highly mobile resistance genes, and multiple instances of resistance mutation evolution. Continuing selection of Sonchus oleraceus populations with ALS‐inhibiting herbicides has resulted in the accumulation of additional mutations within the ALS gene. New practices to control herbicide‐resistant S. oleraceus should be examined, and control should focus on reducing seed set and dispersal to prevent the spread of emerging cases of resistance. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.
Publisher: Cambridge University Press (CUP)
Date: 09-12-2020
DOI: 10.1017/WET.2020.134
Abstract: In southern Australia, annual sowthistle and prickly lettuce have become more prevalent following the adoption of reduced tillage cropping systems. They are especially problematic in lentil and other pulse crops, which are weakly competitive and have few herbicide options available for POST control of broadleaf weeds. This study aimed to evaluate the influence of management in a previous cereal crop on weed densities in a subsequent crop. At two field sites, crop seeding density and POST herbicide treatments (a conventional choice that included metsulfuron-methyl and MCPA and a proactive choice that included bromoxynil, picolinafen, and MCPA) were applied to a wheat crop, and weed density was assessed at the beginning of the following season to measure for a legacy effect of the treatments. Study site populations were also screened for herbicide resistance and were found to have high (≥90% survival) ALS inhibitor resistance. Crop competition treatments had no effect on weed populations, and effects of herbicide treatment were significant at only one of the sites. At this site, both herbicide treatments had lower weed densities than the nontreated in the first year, but the legacy effect was only significant for annual sowthistle density in the proactive treatment. At both sites, even where weeds were extremely sparse or completely controlled following herbicide treatment in the first year, moderate densities were observed the following year, indicating that colonization from the seedbank or adjacent areas could be contributing to weed numbers. Weed density assessments and accurate knowledge of the herbicide resistance status of target weeds should guide herbicide selection to maximize control.
No related grants have been discovered for Alicia Merriam.