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United States Department of Agriculture

Agricultural Research Service

Research Project: BIOLOGICALLY AND ECOLOGICALLY BASED KNOWLEDGE FOR INTEGRATED WEED MANAGEMENT SYSTEMS Title: Wide distribution of the waterhemp (Amaranthus tuberculatus) delta-G210 PPX2 mutation, which confers resistance to PPO-inhibiting herbicides

Authors
item Thinglum, K -
item Riggins, C -
item Davis, Adam
item Bradley, K -
item Al-Khatib, K -
item Tranel, P -

Submitted to: Weed Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 14, 2010
Publication Date: January 1, 2011
Citation: Thinglum, K., Riggins, C.W., Davis, A.S., Bradley, K., Al-Khatib, K., Tranel, P. 2011. Wide distribution of the waterhemp (Amaranthus tuberculatus) delta-G210 PPX2 mutation, which confers resistance to PPO-inhibiting herbicides. Weed Science. 59(1):22-27.

Interpretive Summary: Herbicide resistance in agricultural weeds is a problem that is increasing in incidence and severity in the northern corn belt of the U.S. Common waterhemp (Amaranthus tuberculatus), indigenous to the midwest U.S., has been particularly troublesome with respect to herbicide resistance. Characteristics of this species that make it prone to developing herbicide resistance include a) dioecious populations (male and female plants), ensuring outcrossing, b) enormously high seed production (up to 1,000,000 seeds per plant), and c) copious pollen production, enabling long-distance transport of herbicide resistance traits. Resistance in waterhemp to herbicides that inhibit protoporphyrinogen oxidase (PPO) previously was shown to result from the deletion of a glycine codon at position 210 in the PPO-encoding gene, PPX2. Our objective was to determine if this same mechanism accounted for resistance in geographically separated populations – from Illinois, Kansas, and Missouri – and, if so, to determine if the resistance mutation was independently selected. Dose-response data were consistent with the hypothesis that the populations contained the same resistance mechanism. Direct evidence in support of this hypothesis was provided by DNA sequencing, which showed that nearly all resistant plants evaluated contained the glycine-210 mutation. A variable region of the PPX2 gene was sequenced and resulting sequences were aligned and organized into a phylogenetic tree. The phylogenetic tree did not reveal clear clustering by either geography or phenotype (resistant vs. sensitive). Possibly recombination within the PPX2 gene has masked its evolutionary history.

Technical Abstract: Resistance in waterhemp to herbicides that inhibit protoporphyrinogen oxidase (PPO) previously was shown to result from the deletion of a glycine codon at position 210 (delta G210) in the PPO-encoding gene, PPX2. Research was conducted to determine if this same mechanism accounted for resistance in geographically separated populations – from Illinois, Kansas, and Missouri – and, if so, to determine if the resistance mutation was independently selected. A dose-response study with lactofen indicated that the resistant populations had different levels of resistance. These differences, however, could be accounted for by different frequencies of resistant individuals within populations and, therefore, the dose-response data were consistent with the hypothesis that the populations contained the same resistance mechanism. Direct evidence in support of this hypothesis was provided by DNA sequencing, which showed that nearly all resistant plants evaluated contained the 'G210 mutation. A variable region of the PPX2 gene was sequenced and resulting sequences were aligned and organized into a phylogenetic tree. The phylogenetic tree did not reveal clear clustering by either geography or phenotype (resistant vs. sensitive). Possibly recombination within the PPX2 gene has masked its evolutionary history.

Last Modified: 10/25/2014
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