An investigation into the mode of action and selectivity of three 3,6-dichloropicolinic acid

Thompson, L.M.L., 1989. An investigation into the mode of action and selectivity of three 3,6-dichloropicolinic acid. PhD, Nottingham Trent University.

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The mode of action and selectivity of the herbicide 3,6-dichloropicolinic acid (clopyralid) was examined in three plant species under glasshouse and controlled environment conditions. At the growth stages used Matricaria inodora was susceptible, Galixim aparine mildly susceptible and Beta vulgaris tolerant to the herbicide when applied at concentrations ranging from 6.25 to 400 g ai. ha-1. Visual symptom development was characteristic of auxin-type compounds with rapid and sustained epinasty in susceptible species. This auxin-type activity was partially confirmed in a study of levels of key metabolites in treated plants. Herbicide was retained in significant amounts on the leaves of each species and differential sensitivity was not accounted for by differences in the extent of uptake or translocation, since the herbicide was absorbed into leaves of each species and rapidly translocated in the phloem to the primary growing points as shown by autoradiography. Differences were measured in uptake and translocation of radiolabelled clopyralid droplets between sprayed and unsprayed plants and according to the application method used. Differences in the extent and pattern of metabolism of clopyralid were recorded in the test species. Field rate clopyralid (100 g ai. ha-1) increased the rate of photosynthesis in the third leaf of intact M. inodora plants up to twenty four hours after treatment. B. vulgaris showed no response. Preliminary experiments also recorded clopyralid effects on both abaxial and adaxial stomatal apertures in third leaf M. inodora and B. vulgaris tissue. Stomatal effects were greatest in the susceptible species where the range of stomatal apertures was restricted by clopyralid. Ethylene evolution was rapidly increased by a range of clopyralid concentrations in M. inodora third leaf explants. A clear dose response pattern emerged and it was shown by the use of the precursor ACC and ethylene biosynthesis inhibitors cobalt and AVG that the effect, which was absent in tolerant B. vulgaris, was a symptom of herbicide action and not the cause of the visually observed herbicide damage which appeared concurrently in the explants. These findings were discussed in relation to the literature and hypotheses presented to account for the observed selectivity of clopyralid in these species.

Item Type: Thesis
Creators: Thompson, L.M.L.
Date: 1989
ISBN: 9781369313994
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 its 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: 17 Sep 2020 15:54
Last Modified: 19 Jul 2023 10:18

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