Abstract
The effect of the herbicide dinoseb (2-sec-butyl-4,6-dinitrophenol) on the symbiotic nitrogen fixation of red clover ( Trifolium pratense cv. Venla) was studied in field, greenhouse and laboratory experiments. In the field, the herbicide reduced the levels of nitrogenase (C 2H 2) activity of the plants up to 18 days after treatment, but increased the yields compared to hand-weeded and unweeded controls. Rhizobium strains isolated from root nodules of plants treated with dinoseb showed resistance to the herbicide when grown on laboratory media containing dinoseb. However, in a pot experiment, inoculation with a strain which grew in the presence of 200 μg dinoseb ml −1 did not improve the performance of red clover treated with dinoseb. In the pot experiment dinoseb inhibited nitrogenase activity when sprayed on the leaves, but not when added to the growth medium. Application of starter nitrogen did not influence the effect of dinoseb. The results suggest that dinoseb did not act directly on the nodules, but affected nitrogen fixation by damaging the photosynthetic parts of the plant.
Published Version
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