Studies into the interactions between ozone pollution and herbicides in UK crops

Dixon, J., 2000. Studies into the interactions between ozone pollution and herbicides in UK crops. PhD, Nottingham Trent University.

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During the growing period, spring crops are treated with early post-emergence herbicides at times when episodes of ozone pollution are likely to occur. Therefore, there is the possibility of interactive effects between ozone and the herbicide. To investigate this likelihood, laboratory experiments were conducted in which two to three leaf seedlings of sugarbeet (Beta vulgaris), spring barley (Hordeum vulgare) and spring oilseed rape (Brassica napus) were exposed to a simulated two day ozone episode (100 nl 1-1, 7 h d-1) and/or treatment with field rate herbicide (diclofop-methyl, clopyralid, phenmedipham, mecoprop-p and metazachlor).

A preliminary study was carried out to determine the response of the crops to various rates of herbicide application. Clopyralid exerted no significant effects on spring barley or sugarbeet. Diclofop-methyl had no significant effects on the spring barley cvs. Tyne and Nugget, but decreased shoot dry weight in Sherpa and Corgi. Treatment with fenpropimorph, for the control of powdery mildew, produced varied results dependent on the cultivar. Mecoprop-p reduced the shoot dry weight of the barley cultivar Nugget. Phenmedipharm reduced the shoot dry weight of all 3 sugarbeet CVS. Application of diclofop-methyl did not affect shoot dry weight of the sugarbeet cultivars. Amethyst, Celt and Saxon. Shoot dry weight of oilseed rape was not affected by any of the herbicides and only diclofop-methyl induced visible symptoms of injury. Damage caused by diclofop-methyl was in the form of round chlorotic areas, indicative of contact injury.

Exposure to a simulated two day ozone episode (100 nl 1-1, 7 h d-1) did not have consistent effects on shoot dry weight of oilseed rape and barley. Ozone reduced shoot dry weight in sugarbeet only when the plants were older (25 d after sowing) at the time of exposure.

Growth analyses indicated interactive effects in sugarbeet (cv. Saxon) treated with ozone and phenmedipham and spring oilseed rape (cvs. Starlight and Galaxy) treated with ozone and clopyralid. The remaining experiments all revealed no more or less than additive effects of the herbicides and ozone treatment.

Physiological and biochemical studies were then undertaken to determine the nature of the interaction between ozone pollution and phenmedipham in sugarbeet cv. Saxon. Exposure to phenmedipham alone or ozone followed by phenmedipham reduced net photosynthesis by over 56 % and stomatal conductance by 49 % compared to the control. However, reductions in total chlorophyll and carotenoid content were both intermediate between ozone (small reduction) and phenmedipham (large reduction), although the interactive effect was not significant. Membrane leakage studies indicated that the response of leaves treated with ozone plus phenmedipham was between that of the herbicide and ozone. Determinations of the leachate cation content indicated treatment with phenmedipham increased the leakage of sodium, potassium and magnesium from leaf tissue, whilst ozone had no effect on leakage of cations.

Ozone increased the activities of the antioxidant scavengers, monodehydroascorbate reductase and guaiacol peroxidase, 3 d after exposure, in sugarbeet. Phenmedipham initially elevated the activities of monodehydroascorbate reductase, glutathione reductase, guaiacol peroxidase and glutathione S-transferase and decreased the content of glutathione.

When exposed to ozone prior to the application of phenmedipham, the activities of all measured antioxidant enzymes, except SOD, were elevated 2 d after herbicide treatment. Furthermore, some of the enzymes (monodehydroascorbate reductase, glutathione reductase and guaiacol peroxidase) exhibited increases in activity that were greater than the additive effects of the individual treatments after 1 d. This response was reversed 2 d after phenmedipham treatment. Protein contents exhibited a less than additive interaction between days 2 and 4, whilst glutathione reductase, catalase and guaiacol peroxidase also exhibited a less than additive interaction 4 d after herbicide application. Since physiological effects (photosynthetic rate, stomatal conductance, membrane leakage) were not greater in plants treated with ozone and phemnedipham, this might suggest that ozone was increasing the titre of the enzymes sufficiently, to lead to an increased tolerance to phenmedipham damage.

Item Type: Thesis
Creators: Dixon, J.
Date: 2000
ISBN: 9781369312959
Rights: This copy of the thesis has been supplied on condition that anyone who consults it is understood to recognise that its copyright rests with the author and that no quotation from the thesis and no information derived from it may be published without the author's prior written consent.
Divisions: Schools > School of Science and Technology
Record created by: Jeremy Silvester
Date Added: 27 Aug 2020 15:34
Last Modified: 15 Jun 2023 09:42

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