Population structure of ALS‐inhibiting herbicide‐resistant Sonchus oleraceus in South Australia

Abstract

Background 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 amphidiploid species, and combines this with analyses of population structure and gene flow. Results 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 samples were collected from across a single field on the YP and the ALS gene was sequenced for all these individuals. 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. Conclusions 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.

Point mutations including a novel Pro‐197‐Phe mutation confer cross‐resistance to acetolactate synthase (ALS) inhibiting herbicides in Lactuca serriola in Australia

“…Plants were grown outdoors during the 2019 winter growing season (May–July) at the Waite Campus of the University of Adelaide in Urrbrae, SA, Australia (34.97° S, 138.64° E) Average season temperature ranged from 22.4 °C maximum to 1.7 °C minimum, with 206 mm rainfall received between May and July 19 ; plants were also watered as required. Herbicide treatments were applied at the four‐ or five‐leaf stage with laboratory sprayer equipment, as described previously, 20 to two pots (12 plants) per population. Chlorsulfuron (Glean®, Dupont Pty Ltd, Australia) was applied at 15 g a.i.…”

“…Two fragments of the ALS gene containing all nine sites known to contain mutations endowing resistance were amplified via polymerase chain reaction (PCR), using primers and methods described previously. 20 Briefly, PCR reactions of 15 μL contained 1 μL of extracted DNA (containing between 5 and 100 ng DNA), 7.5 μL of 2× MyFi mix (Bioline, Eveleigh, NSW, Australia), and 0.6 μL of a 10 mM stock of each of the forward and reverse primers of either pair of primers for fragment 1 or fragment 2. Thermocycling conditions were: 1 min denaturing at 95 °C, 35 cycles of 15 s denaturation at 95 °C, 15 s of annealing at 58 °C and 15 s of extension at 72 °C (or 20 s extension for fragment 2).…”

“…The genetic structure of the populations was analysed using genotyping-by-sequencing (GBS), as described previously. 20 Briefly, DNA samples, extracted for ALS sequencing in Section 2.3, were normalized to 2 ng μl −1 and six libraries prepared by multiplexing into 6 × 96-well plates using DNA barcodes. The libraries were submitted for Illumina sequencing by Novogene (NovogeneAIT Genomics, Singapore).…”