Differential Hormetic Response of Fenoxaprop-p-Ethyl Resistant and Susceptible Phalaris minor Populations: a Potential Factor in Resistance Evolution

Abstract

Resistance evolution in weeds against all major herbicide groups demand investigations to identify various factors responsible for resistance development. Herbicide hormesis has not yet been included in the list of factors promoting the evolution of resistance. Studies were conducted to evaluate the degree of hormesis in fenoxaprop-p-ethyl susceptible and resistant Phalaris minor to provide a first indication of whether hormesis is a potential factor in the development of resistance. In the first experiment, a wide range of doses up to 160% of the recommended field rate was used to identify potential hormetic doses for resistant and susceptible P. minor populations. Doses below 40% have been designated as potential hormetic doses. In the second experiment, ten different doses of fenoxaprop below 40% (0, 2, 4, 8, 12, 16, 20, 24, 28 and 32% of the recommended rate) were sprayed at the 4-5 leaf stage of both resistant and susceptible P. minor populations. At fifteen days after spraying, dose range of 2-12% and 2-20% caused a significant increase (up to 22% and 24%) in growth traits of susceptible and resistant populations, respectively. At maturity, dose range of 2-12% for susceptible and 2-24% for resistant populations caused a significant increase (up to 20% and 57%) in growth and seed production potential (13% and 17%), respectively. The upper limit of the hormetic dose range (16 to 24%) for the resistant population was inhibitory for the susceptible populations. These results indicate that fenoxaprop hormesis could play a vital role in the evolution of fenoxaprop resistance in P. minor.

Response of glyphosate-resistant and susceptible biotypes of Echinochloa colona to low doses of glyphosate in different soil moisture conditions

“…Hormesis could theoretically cause better growth and increased competitiveness in both biotypes of E. colona without considering mechanical and precision application technologies for glyphosate spraying. There is a probability that growth stimulation via hormesis, makes weeds more competitive, more reproductive and more resistant to other control treatments and it can alter dynamics of weed-crop competition [10,14,42,43]. If stimulated weeds are resistant to herbicides in the field, hormesis can directly facilitate the evolution of resistance by improving their growth and reproductive output [6,17,42,44].…”

Glyphosate-induced hormesis: impact on seedling growth and reproductive potential of common sowthistle (Sonchus oleraceus)

“…Under such scenarios, changes in weed species composition, and hence herbicide susceptibility, are expected (Belz and Duke 2017;Cedergreen 2008aCedergreen , 2008b. Growth stimulation caused by ultralow herbicide doses has recently been demonstrated as an important factor conducive to herbicide-resistance development, and hormetically boosted resistant biotypes are expected to be more competitive (Farooq et al 2019). Differential hormetic responses were exhibited by fenoxaprop p-ethyl resistant and susceptible populations of canary grass (Phalaris minor Retz.).…”

“…Differential hormetic responses were exhibited by fenoxaprop p-ethyl resistant and susceptible populations of canary grass (Phalaris minor Retz.). The upper limit of stimulatory hormetic dose (16% to 24% of the recommended application rate) for the resistant population was inhibitory for the susceptible population (Farooq et al 2019). Likewise, another study found a 54% increase in biomass of an acetyl-CoA carboxylase target-site resistant (TSR) biotype of blackgrass (Alopecurus myosuroides Huds.)…”

The effect of pre-sowing seed treatment on seedlings growth rate and their excretory activity

“…It was shown that the irradiation of seeds before sowing provides an increase in productivity of about 5-20% (Farooq et al, 2019). Such an increase in yield after irradiation or after the action of other physical factors is explained by the presence of a metabolic acceleration zone on the dose curve and the yield as well.…”