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

Abstract

To evaluate the hormetic effect of glyphosate on Echinochloa colona, two pot studies were done in the screenhouse at the Gatton Campus, the University of Queensland, Australia. Glyphosate was sprayed at the 3-4 leaf stage using different doses [(0, 5, 10, 20, 40, 80 and 800 g a.e. ha-1) and (0, 2.5, 5, 10, 20 and 800 g a.e. ha-1)] in the first and second study, respectively. In the second study, two soil moistures (adequately-watered and waterstressed), and two E. colona biotypes, glyphosate-resistant and glyphosate-susceptible, were included. In both studies, plants that were treated with glyphosate at 2.5-40 g ha-1 grew taller and produced more leaves, tillers, inflorescences and seeds than the control treatment. In the first study, 5 g ha-1 glyphosate resulted in the maximum aboveground biomass (increase of 34% to 118%) compared with the control treatment. In the second study, the adequately-watered and glyphosate low dose treatments caused an increase in all the measured growth parameters for both biotypes. For example, total dry biomass was increased by 64% and 54% at 5 g ha-1 in the adequately-watered treatments for the resistant and susceptible biotypes, respectively, compared with the control treatment. All measured traits tended to decrease with increasing water stress and the stimulative growth of low doses of glyphosate could not compensate for the water stress effect. The results of both studies showed a hormetic effect of low doses of glyphosate on E. colona biotypes and such growth stimulation was significant in the range of 5 to 10 g ha-1 glyphosate. Water availability was found to be effective in modulating the stimulatory outcomes of glyphosate-induced hormesis. No significant difference was observed between the resistant and susceptible biotypes for hormesis phenomenon. The study showed the importance of precise herbicide application for suppressing weed growth and herbicide resistance evolution.

Glyphosate hormesis mitigates the effect of water deficit in safflower (Carthamus tinctorius L.)

“…The absorption of low doses of glyphosate may vary according to the water conditions of the plant. Plants may require higher doses of glyphosate when under water deficit, this effect being due to the translocation capacity of the herbicide in the plant 28,32 . The hormeticdose for stimulation in plants under water deficit was on average lower than under no water stress (60.27 ± 11.30 g a.e.…”

“…Studies on the interaction between water deficit and glyphosate hormesis in plants are rare; however, previous studies with Phaseolus vulgaris have shown a greater tolerance to water stress in the presence of low doses of glyphosate 31 . Research has shown that the effectiveness of glyphosate is dependent on climatic conditions, the susceptibility of the crop to glyphosate and the stage of plant development, however this work was conducted mostly with weeds 28,32 …”

“…26 It is increasingly evident that there is a need for practical approaches to improve crop production involving mechanisms that vary by species and growth stage, in addition to environmental factors related to crops and agro-ecosystems. 11,27,28 Several environmental factors such as water availability, mineral nutrition, temperature, light intensity and CO 2 concentration can influence hormetic stimuli. 27,29 Knowledge of these interactions is needed if glyphosate hormesis is to improve crop production.…”

“…31 Research has shown that the effectiveness of glyphosate is dependent on climatic conditions, the susceptibility of the crop to glyphosate and the stage of plant development, however this work was conducted mostly with weeds. 28,32 For example, negative effects of low doses of glyphosate under conditions of water deficit were found in two biotypes of Echinochloa colona (resistant and susceptible to glyphosate). All the growth parameters tended to decrease under water deficit, and even low doses of glyphosate were not able to compensate for the significant reduction in biomass in sensitive plants.…”

“…All the growth parameters tended to decrease under water deficit, and even low doses of glyphosate were not able to compensate for the significant reduction in biomass in sensitive plants. 28 In another study using the same biotypes, plants resistant to glyphosate treated with 1140 g a.e. ha −1 glyphosate had an increased survival rate of 62% under water stress, whereas the sensitive biotype showed reductions in biomass of 62% and 92% at glyphosate doses of 720 and 1440 a.e.…”