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ARS Home » Midwest Area » Urbana, Illinois » Global Change and Photosynthesis Research » Research » Publications at this Location » Publication #308293
Title: Non-target-site resistance to ALS inhibitors in waterhemp (Amaranthus tuberculatus)

Author
item GUO, J - University Of Illinois
item RIGGINS, C - University Of Illinois
item HAUSMAN, N - University Of Illinois
item HAGER, A - University Of Illinois
item RIECHERS, D - University Of Illinois
item Davis, Adam
item TRANEL, P - University Of Illinois

Submitted to: Weed Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/12/2014
Publication Date: 4/1/2015
Citation: Guo, J., Riggins, C.W., Hausman, N.E., Hager, A.G., Riechers, D.E., Davis, A.S., Tranel, P.J. 2015. Non-target-site resistance to ALS inhibitors in waterhemp (Amaranthus tuberculatus). Weed Science. 63:399-407.

Interpretive Summary: Crop production and food security are increasingly threatened by multiple herbicide resistant weeds, in which a given weed species no longer responds to two or more herbicide modes of action. Common waterhemp, an economically important weed of midwest U.S. field crops, is genetically diverse and is capable of very high seed production, traits which have helped it become resistant to several herbicide modes of action. A waterhemp population (MCR) previously characterized as resistant to HPPD and PSII inhibitors was found to have two different resistance responses to ALS inhibitors. Plants from the MCR population exhibiting high resistance to ALS inhibitors contained the commonly found Trp574Leu ALS amino acid substitution (target site resistance), whereas plants with only moderate resistance did not have this substitution. A population (JG11) was derived from the MCR population in which the moderate-resistance trait was isolated from the Trp574Leu mutation. Results from DNA sequencing and ALS enzyme assays demonstrated that resistance to ALS inhibitors in the JG11 population was not due to an altered site of action. The original MCR waterhemp population contains multiple resistance to inhibitors of HPPD, PSII, and ALS through a combination of target and non-target-site mechanisms. Non-target-site resistance to ALS has been rarely documented in broadleaf weeds , and adds to the growing list of resistance traits evolved in waterhemp.

Technical Abstract: A waterhemp population (MCR) previously characterized as resistant to 4-hyroxyphenylpyruvate dioxygenase (HPPD) and photosystem II (PSII) inhibitors was found to have two different resistance responses to acetolactate synthase (ALS) inhibitors. Plants from the MCR population exhibiting high resistance to ALS inhibitors contained the commonly found Trp574Leu ALS amino acid substitution, whereas plants with only moderate resistance did not have this substitution. A population (JG11) was derived from the MCR population in which the moderate-resistance trait was isolated from the Trp574Leu mutation. Results from DNA sequencing and ALS enzyme assays demonstrated that resistance to ALS inhibitors in the JG11 population was not do to an altered site of action. This non-target-site ALS-inhibitor resistance was characterized with whole-plant dose-response experiments using herbicides from each of the five commercialized families of ALS-inhibiting herbicides. Resistance ratios of 3 to 90 were obtained from the seven herbicides evaluated. When plants were treated with the cytochrome P450 inhibitor malathion in combination with herbicide, plants were injured to levels observed when a non-resistant population was treated with herbicide alone. The original MCR waterhemp population contains multiple resistance to inhibitors of HPPD, PSII, and ALS through a combination of target and non-target-site mechanisms. Non-target-site resistance to ALS has been rarely documented in eudicot weeds , and adds to the growing list of resistance traits evolved in waterhemp.