HerbBi - Herbizid-vermittelte biphasische Reaktionen in Pflanzen
Zusammenfassung der Projektergebnisse
Small amounts of herbicides or other phytotoxins such as allelochemicals or environmental pollutants can promote plant growth, a phenomenon that is known as hormesis. Agricultural scientist Dr. Regina Belz's team at the University of Hohenheim in Stuttgart has been investigating the importance and consequences of herbicide hormesis for agriculture, environment and evolution in cooperation with (inter-)national partners. The project particularly targeted the effects this phenomenon can have on plant production, chemical weed control and other plants that are not the target of herbicide control measures. Results showed that hormesis is far more than the simple promotion of plant growth. The effect is complex and depends on many factors, starting from the genetically determined characteristics and the growth stage of the exposed plants, through the growth conditions to the dosage and exposure scenario of the herbicide and its interaction with other environmental influences. The lowdose herbicide stress is suspected to trigger reactions in cells, which ultimately lead to a kind of resilience and can make the plant and its offspring fitter against renewed stress effects. Herbicide hormesis has potential effects on agriculture, environment and evolution. On the one hand, herbicide hormesis could be used to increase crop yields and make crops more stressresilient. Practically, the unpredictability of hormesis makes the phenomenon too risky for general crop production. The hormesis effect and influencing factors have been investigated in several experiments showing that the unpredictability mainly stems from environmental growth conditions, from species- and cultivar-dependent differences in hormetic responsiveness, from selective effects on individuals within plant populations, from the plant trait measured, and/or from other factors influencing plant growth (e.g., fertilization, joint effects with other toxins). On the other hand, hormesis also occurs after regular herbicide applications for weed control when crops, weeds or wild plants are mistakably exposed to low doses on the treated area or beyond, e.g. because wind and weather conditions are unfavorable. When herbicides are applied to combat weeds, there is a risk for hormetic effects that go beyond the goal of weed control on the applied area at every application. This could have far-reaching economic, environmental and/or evolutionary consequences, but knowledge on herbicide hormesis does not yet allow these consequences to be profoundly assessed. This is why hormetic side effects of herbicide applications were the main topic of the current research project. Of particularly interest were weed plants such as ryegrass, chamomile or goosefoot, which are known to be resistant to herbicides very often. Moreover, basic experiments with large model populations have been carried out with crop plants such as barley or lettuce. The fact that hormesis occurs highly reproducible and pronounced with glyphosate, currently the most widely used herbicide active ingredient, made this substance a main test stimulant besides other active herbicide ingredients, such as PSII-, ACCase- or ALS-herbicides or natural plant phytotoxins that block various metabolic pathways of plants. Herbicide hormesis promotes the development of weed resistance and has a lasting effect on plant populations. Laboratory and greenhouse trials showed that chemical control measures not only favor herbicide-resistant weeds, but also make selected weeds fitter and more reproductive via hormesis. The seeds of hormetically stimulated plants can be more numerous, larger and heavier, which gives their seedlings a further survival advantage. The offspring of hormetically-stimulated parents further proved more resilient towards renewed herbicide stress and hormesis was more pronounced in them. It is thus suggested that herbicide hormesis can prime plants across generations and greatly facilitate the evolution and dynamics of herbicide resistance evolution. In addition, such hormesis-induced selection for and against certain subpopulations can also occur in exposed natural plant populations and lead to a shift in the distribution of plant traits within the overall population. The extremes are particularly affected, i.e. the number of particularly slow-growing, sensitive individuals or of particularly fast-growing, resilient plants is changed and thus the adaptability of the population to other stress. In the longer term, such phenotype shifts could lead to genotypic adaptations in plant populations along with changes in herbicide susceptibility or resistance status followed by cascading effects on herbicide efficacy, biodiversity and ecosystem processes. Outlook. The project considerably advanced our knowledge on herbicide hormesis and its significance for resistance evolution, the sustainability of chemical weed control, and herbicide risk assessment. Despite this, still a lot of work is needed before we know whether and how hormesis is to consider for practical and (agro-)ecological impacts of herbicide use. However, in view of the quantities of herbicides applied annually, we should understand the full impact of this phenomenon.
Projektbezogene Publikationen (Auswahl)
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(2017): Herbicide-mediated hormesis. In Duke SO, Kudsk P., Solomon K (eds.): Pesticide dose: effects on the environment and target and non-target organisms. Amer Chem Soc Symp Ser 1249:135-148
Belz RG, Duke SO
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(2017): Predicting biphasic responses in binary mixtures: Pelargonic acid versus glyphosate. Chemosphere 178:88-98
Belz RG, Piepho HP
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(2018): Does selective hormesis impact herbicide resistance evolution in weeds? ACCase-resistant populations of Alopecurus myosuroides Huds. as a case study. Pest Management Science 74(8):1880-1891
Belz RG, Farooq MB, Wagner J
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(2018): Herbicide hormesis can act as a driver of resistance evolution in weeds – PSII-target-site resistance in Chenopodium album L. as a case study. Pest Management Science 74(12):2874-2883
Belz RG
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(2019): Low toxin doses change plant size distribution in dense populations – Glyphosate exposed Hordeum vulgare as a greenhouse case study. Environment International 132
Belz RG, Sinkkonen A
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(2019): Realistic low-doses of two emerging contaminants change size distribution of an annual flowering plant population. Ecotoxicology 28:732-743
Patama M, Belz RG, Sinkkonen A
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(2020). Generationsübergreifende Auswirkungen von Herbizid-Hormesis bei PSII-Target Site resistentem Chenopodium album L. Julius-Kühn-Archiv 464:498-504
Belz RG
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Low herbicide doses can change the responses of weeds to subsequent treatments in the next generation – metamitron exposed PSII-target-site resistant Chenopodium album as a case study. Pest Management Science
Belz RG
