Target-Site Point Mutation Conferring Resistance to ALS Herbicides in Italian Ryegrass (Lolium multiflorum L.)

Abstract

Italian ryegrass (Lolium multiflorum L.) is a major weed problem in wheat fields in Turkey. Continued use of herbicides has resulted in the selection of many herbicide-resistant weeds. This study aims to determine the resistance pattern of acetolactate synthase (ALS) inhibiting herbicides related to L. multiflorum in wheat cultivation areas from Turkey and the solution proposals to be brought to the problems. After seed collection, whole-plant bioassays were conducted to confirm herbicide resistance in L. multiflorum and determine the resistance level to available herbicides in greenhouse experiments. The treatments included three post-emergence herbicides: Perun 75 WG (7.5% pyroxsulam + 7.5% cloquintocet-mexyl), Atlantis WG (30 g/kg mesosulfuron-methyl and 6 g/kg iodosulfuron-methyl-sodium), Attribut Super (6.75% propoxycarbazone-sodium + 4.5% mesosulfuron-methyl). In preliminary bioassay, 43 of 79 accessions were suspicious for resistance to the commercial dose of ALS inhibiting herbicides showing less than 80% efficacy. Dose-response experiment data was fitted to an asymmetric sigmoid curve to obtain ED50 values. Some biotypes (BAL-43, BAL-8, BUR-11, COR-21, ESK-2 and ESK-23) showed cross-resistance to ALS-inhibiting herbicides. In addition, COR-21 and BAL-43 biotypes were strongly resistant to herbicides and had 100% survival even at 16 times the recommended rates. Some biotypes were selected for sequence analysis at Ala-122, Pro-197, Ala-205, Asp -376, Trp -574, Ser-653 positions. Amino acid substitution was detected in L. multiflorum of Pro-to-Leu at position 197 (GenBank accession MK922479). Through research and findings, some basic resistance-management strategies have been exhibited. One of the most important is the diversification of herbicide mode of action. To mitigate weed resistance, it is important that farmers have to use a variety of weed control strategies when possible. As a global approach, strong policies should be produced for the problem of resistance in weeds.