Identification of the first glyphosate-resistant capeweed (Arctotheca calendula) population.

Abstract

BACKGROUND\nGlyphosate is routinely used in Australia to control the Arctotheca species Arctotheca calendula (L.) Levyns (referred hereinafter as capeweed). This study identifies the first global case of field-evolved glyphosate-resistant capeweed, collected from the grainbelt of Western Australia.\n\n\nRESULTS\nIn 2020, a capeweed biotype that was collected from Borden in the southern Western Australian grainbelt was confirmed to be glyphosate-resistant (referred hereinafter as Spence population). When compared to the pooled mortality of six field-collected, glyphosate susceptible capeweed populations (S1, S2, S3, S4, S5, and S6), the Spence population was found >11-fold more resistant to glyphosate than the pooled results of the susceptible populations (S1-S6) at the LD50 level. The growth of the Spence population was also less affected, requiring >13-fold more glyphosate to reduce growth than the pooled susceptible populations at the GR50 level. Sequencing of the plastidic EPSPS gene indicated no known single gene mutation imparting glyphosate resistance. This study, however, did not investigate any other known mechanisms that impart glyphosate resistance. When screened at the field-applied rate, this Spence population was also found to survive an inhibitor of acetolactate synthase (ALS) (metosulam) and an inhibitor of phytoene desaturase (diflufenican).\n\n\nCONCLUSIONS\nThis is the first confirmation of glyphosate resistance evolution in a capeweed population globally. With capeweed resistance already confirmed to photosystem-I inhibiting herbicides (paraquat and diquat)1 , this study emphasises the importance of using integrated measures that do not depend only on the use of non-selective herbicides for controlling herbicide resistance-prone capeweed populations. This article is protected by copyright. All rights reserved.