Studies into the differential activity of the hydroxybenzonitrile herbicides on various weed species

Sanders, G.E., 1984. Studies into the differential activity of the hydroxybenzonitrile herbicides on various weed species. PhD, Nottingham Trent University.

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The mechanism of action and selectivity of ioxynil and bromoxynil salts was investigated in Matricaria inodora. Stellaria media and Viola arvensis. The differential activity was characterized by monitoring symptoms such as chlorosis and necrosis, and by studying metabolic changes in sprayed plants, M. inodora, S. media and V. arvensis were susceptible, moderately susceptible and moderately resistant to ioxynil, and acutely susceptible, moderately resistant and resistant to bromoxynil respectively. Herbicide retention and leaf surface characteristics did not contribute to the differential response.

Greater than 80% of penetrated 14C-herbicide remained in the treated leaves and contributed to chlorosis and necrosis. CO2-fixation was rapidly inhibited and ultrastructural changes developed within 48 hours. In susceptible interactions .ioxynil-induced thylakoid swelling and chloroplast disruption, typical of photo oxidative damage. Such changes were less apparent with bromoxynil. Gellular disruption in M. inodora suggested an uncoupling and/or permeability action of bromoxynil. In V. arvensis, where a partial recovery of CO2 fixation occurred, adaptive changes in chloroplast ultrastructure such as broader and higher granal stacks, were evident.
14C-bromoxynil was more mobile than 14C-ioxynil and significant inter-specific differences were found in the speed and direction of herbicide movement. A far greater proportion of translocated 14C-ioxynil was recovered from the apex of susceptible M. inodora than that of moderately resistant V. arvensis. Bromoxynil appeared to be metabolized in V. arvensis and to a lesser extent S. media which may contribute towards reduced phytotoxicity in these species. A significant proportion of 14C-hydroxybenzonitrile was undetected due to volatilization from the leaf surface.

Interspecific differences in herbicide activity were not apparent at the thylakoid level. Ioxynil was 3-4 times more effective as an inhibitory uncoupler in chloroplasts isolated from the three species. In radiolabelled displacement studies ioxynil partially replaced bound -bromoxynil, whereas bromoxynil did not replace bound 14C-ioxynil, indicating stronger ioxynil binding.

Item Type: Thesis
Creators: Sanders, G.E.
Date: 1984
ISBN: 9781369325706
Divisions: Schools > School of Science and Technology
Record created by: Laura Ward
Date Added: 08 Jul 2021 08:37
Last Modified: 10 Apr 2024 15:55

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