Abstract
AbstractWaterhemp [Amaranthus tuberculatus (Moq.) Sauer] is one of the most troublesome agronomic weeds in the midwestern United States. The rapid evolution and selection of herbicide-resistance traits in A. tuberculatus is a major challenge in managing this species. An A. tuberculatus population, designated CHR, was identified in 2012 in Champaign County, IL, and previously characterized as resistant to herbicides from six site-of-action groups: 2,4-D (Group 4), acetolactate synthase inhibitors (Group 2), protoporphyrinogen oxidase inhibitors (Group 14), 4-hydroxyphenylpyruvate dioxygenase inhibitors (Group 27), photosystem II inhibitors (Group 5), and very-long-chain fatty-acid synthesis inhibitors (Group 15). Recently, ineffective control of CHR was observed in the field after dicamba application. Therefore, this research was initiated to confirm dicamba resistance, quantify the resistance level, and investigate its inheritance in CHR. Multiple field trials were conducted at the CHR location to confirm poor control with dicamba and compare dicamba treatments with other herbicides. Greenhouse trials were conducted to quantify the resistance level in CHR and confirm genetic inheritance of the resistance. In field trials, dicamba did not provide more than 65% control, while glyphosate and glufosinate provided at least 90% control. Multiple accessions were generated from controlled crosses and evaluated in greenhouse trials. Greenhouse dicamba dose–response experiments indicated a resistance level of 5- to 10-fold relative to a sensitive parental line. Dose–response experiments using F1 lines indicated that dicamba resistance was an incompletely dominant trait. Segregation analysis with F2 and backcross populations indicated that dicamba resistance had moderate heritability and was potentially a multigenic trait. Although dicamba resistance was predominantly inherited as a nuclear trait, minor maternal inheritance was not completely ruled out. To our knowledge, CHR is one of the first cases of dicamba resistance in A. tuberculatus. Further studies will focus on elucidating the genes involved in dicamba resistance.
Highlights
Modern agriculture is in constant development to surpass management challenges and achieve the high yields required to feed the exponentially growing world population
Where W1, W2, and W3 are the log (ED50) of the sensitive parent, resistant parent, and F1 population, respectively, calculated from the log-logistic models. Because both biomass and plant area are representing the effects of dicamba on the tested populations, the degree of dominance was calculated for each variable, and the average from each was used as the final value for degree of dominance
When glyphosate was included with 2,4-D, A. tuberculatus control increased to 90%, indicating CHR remains susceptible to glyphosate
Summary
Modern agriculture is in constant development to surpass management challenges and achieve the high yields required to feed the exponentially growing world population. The objectives of this experiments were to: (1) quantify dicamba efficiency and compare it with efficiency of other synthetic auxin and alternative herbicides in the field; (2) characterize the current dicamba effectiveness on CHR via dose– response experiments; and (3) conduct a segregation analysis to identify whether dicamba resistance is a heritable trait in CHR. CHR seeds were collected in 2018 from plants in the field Trial C that survived postemergence-applied dicamba (560 g ae ha–1) and brought to the lab to generate populations.
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