Field-evolved cross-resistance to ALS inhibiting herbicides in redroot pigweed ( Amaranthus retroflexus L.) populations and alternative chemical options for effective control

• Published in: Weed technology 2024-10, p.1-25
• Main Authors: Papapanagiotou, Aristeidis P., Alvanou, Maria V., Giantsis, Ioannis A., Kati, Vaya A., Eleftherohorinos, Ilias G.
• Format: Article
• Language: English
• ISSN: 0890-037X; 1550-2740
• DOI: 10.1017/wet.2024.57

Twelve putative-resistant (R) redroot pigweed populations were collected in sunflower and soybean fields located in northeastern Greece, after repeated exposure to the acetolactate synthase (ALS)-inhibiting herbicides imazamox and tribenuron-methyl. Studies were conducted to determine the resistance status to these two ALS-inhibiting herbicides and evaluate alternative post- and preemergence herbicides for effective control. Two susceptible (S) populations were also included for comparison. Eleven out of the 12 putative-R populations studied in the whole plant dose response pot experiments were characterized as cross-resistant (R) to the imidazolinone imazamox and the sulfonylurea tribenuron-methyl. In contrast, the putative R5 and the two reference populations (S1, S2) populations were found susceptible. Sequencing of the ALS gene revealed that a point mutation (TGG to TTG at position 574) was selected in domain B, where in combination with domain A the majority of point mutations conferring resistance have been detected, resulting in an amino acid substitution from tryptophan (Trp) to leucine (Leu) in the 11 R populations. By contrast, all sequenced plants of the three susceptible populations were found with the wild-type allele encoding Trp574. The labeled rate of the postemergence herbicides tembotrione and dicamba provided fair to excellent control of the populations with ALS cross-resistance. In contrast, at this rate the preemergence herbicides S -metolachlor+terbuthylazine, isoxaflutole, aclonifen, metribuzin, and pendimethalin provided excellent control. These findings strongly suggest that 11 redroot pigweed populations have evolved cross-resistance to ALS-inhibiting herbicides, but viable options for chemical control of this weed still exist.