Submitted to: Pesticide Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 1, 1998
Publication Date: N/A
Interpretive Summary: Sorgoleone is a natural product from the roots of some Sorghum species. By blocking the photosynthesis, it controls weeds the same way some synthetic herbicides do. The objective of this paper is to answer the question: can we mix sorgoleone with synthetic herbicides and get a predictable effect? The results indicate that we generally can get a predicted effect, but the mechanism by which the natural product and the synthetic herbicides act is more complicated than we thought. This information may be useful in development of sorgoleone as a natural herbicide.
Technical Abstract: The inhibitory action of four sorgoleone analogues, isolated from Sorghum bicolor (L.) Moench, and two synthetic inhibitors, diuron and bentazon, was tested by measuring oxygen evolution of thylakoid membranes. The inhibition of oxygen evolution for mixtures of inhibitors was compared with the Additive Dose Model (ADM). ADM assumes that, at a defined response level, the effect of a mixture of inhibitors can be unambiguously expressed by the potency of either of the inhibitors applied separately. The slope of the logistic dose response curves differed between the inhibitors; sorgoleone analogues had the steepest and bentazon the shallowest slope. The difference in slopes makes the interpretation of the isoboles less general and may reflect the differences in the interaction between the natural and the synthetic inhibitors with the binding site. The results suggest that there may be some limitation to ADM, namely that compounds with the same site of action might have different response curves if their mechanism of binding is different. The joint action of inhibitors follow ADM at I50. Therefore, the inhibitors can substitute each other in any mixture ratio, based on the relative potency of the pure inhibitors, without changing each others effect on oxygen evolution. The joint action at I20 and I80 sometimes diverted from ADM.