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The biochemical mode of action of pesticides
Physiological
Plant
Pathologv
(1975) 6, 105-106
Book Review The
Biochemical
Press, London
mode
of Action
of Pesticides.
J. R.
CORBETT.
Academic
(1974). 330 pp. Price: g7.20.
The pesticides dealt with in this book are fungicides (f), insecticides (i), acaricides (a), nematicides (n), herbicides (h) and a few veterinary products. These biocides have been classified irrespective of their use, according to their mechanism of action. Chapters deal successively with chemicals which act primarily on respiration (f, i, a), photosynthesis (h), the nervous system (i, a), plant growth (h, f) and various biosynthetic reactions, including nucleic acid and protein synthesis (f, n, h), carotenoid synthesis (h), lipid synthesis (h, f), chitin synthesis (f’) and other processes; one chapter deals with compounds, mainly fungicides, which act in a non-specific way by reaction with many cell constituents. Finally a number of pesticides are listed with a still unknown mode of action. This approach of the subject by the author seems logical and appropriate, since during recent years much information has become available on the biochemical background of the mode of action of the different types of pesticides. Although many compounds still have to be placed in the chapter on pesticides with unknown mode of action, and the primary site of attack of several other chemicals is not yet precisely known, the value of this classification will increase since rapid progress in this field may be expected. It may be noticed that even during the short period since the author wrote this book, significant information has become available on the mode of action of several compounds listed here as pesticides with an unknown mode of action, e.g. triforine (p. 268) and pyrazophos (p. 270); it also became clear that benomyl does not interfere with DNA synthesis (p. 229), but with the functioning of the spindle, thus inhibiting mitosis. This book provides an excellent survey of the pesticides used in agriculture, and gives their chemical structure. It deals primarily with the mode of action on a molecular basis and considers uptake and metabolism of pesticides only when they are relevant to this topic. The question is raised whether the increasing knowledge of the mechanism of action of biocides will allow us to elucidate the relation between chemical structure and biological activity. The author concludes that, on this basis, design de novo of pesticides with a specific action is not yet possible. For development of new compounds with activity against plant diseases we still have to rely upon random synthesis and screening and upon analogue synthesis, i.e. synthesis of compounds related to a structure that is known to be active. The ready development of resistance to some of the new systemic fungicides is attributed by the author in the first place to a high selection pressure exerted by these compounds. Of more importance, it seems to this reviewer, is the fact that sensitivity to a fungicide which acts specifically at one site may be governed by a
106
Book
review
single gene, which makes development of resistance possible by one mutation; for conventional fungicides, which are as a rule multi-site inhibitors, the situation is quite different. Criticisms such as this one, however, do not detract much from the great merits of this book. The text is written in a clear style and in such a way that it is easy to understand by readers not specialized in chemistry or biochemistry; the relevant background information is outlined in simple terms. Although this might easily lead to a somewhat superficial treatment, the author as a rule has been able to avoid this danger. This book can be highly recommended to all scientists interested in pesticides. J. DEKKER
Plant
Pathologv
(1975) 6, 105-106
Book Review The
Biochemical
Press, London
mode
of Action
of Pesticides.
J. R.
CORBETT.
Academic
(1974). 330 pp. Price: g7.20.
The pesticides dealt with in this book are fungicides (f), insecticides (i), acaricides (a), nematicides (n), herbicides (h) and a few veterinary products. These biocides have been classified irrespective of their use, according to their mechanism of action. Chapters deal successively with chemicals which act primarily on respiration (f, i, a), photosynthesis (h), the nervous system (i, a), plant growth (h, f) and various biosynthetic reactions, including nucleic acid and protein synthesis (f, n, h), carotenoid synthesis (h), lipid synthesis (h, f), chitin synthesis (f’) and other processes; one chapter deals with compounds, mainly fungicides, which act in a non-specific way by reaction with many cell constituents. Finally a number of pesticides are listed with a still unknown mode of action. This approach of the subject by the author seems logical and appropriate, since during recent years much information has become available on the biochemical background of the mode of action of the different types of pesticides. Although many compounds still have to be placed in the chapter on pesticides with unknown mode of action, and the primary site of attack of several other chemicals is not yet precisely known, the value of this classification will increase since rapid progress in this field may be expected. It may be noticed that even during the short period since the author wrote this book, significant information has become available on the mode of action of several compounds listed here as pesticides with an unknown mode of action, e.g. triforine (p. 268) and pyrazophos (p. 270); it also became clear that benomyl does not interfere with DNA synthesis (p. 229), but with the functioning of the spindle, thus inhibiting mitosis. This book provides an excellent survey of the pesticides used in agriculture, and gives their chemical structure. It deals primarily with the mode of action on a molecular basis and considers uptake and metabolism of pesticides only when they are relevant to this topic. The question is raised whether the increasing knowledge of the mechanism of action of biocides will allow us to elucidate the relation between chemical structure and biological activity. The author concludes that, on this basis, design de novo of pesticides with a specific action is not yet possible. For development of new compounds with activity against plant diseases we still have to rely upon random synthesis and screening and upon analogue synthesis, i.e. synthesis of compounds related to a structure that is known to be active. The ready development of resistance to some of the new systemic fungicides is attributed by the author in the first place to a high selection pressure exerted by these compounds. Of more importance, it seems to this reviewer, is the fact that sensitivity to a fungicide which acts specifically at one site may be governed by a
106
Book
review
single gene, which makes development of resistance possible by one mutation; for conventional fungicides, which are as a rule multi-site inhibitors, the situation is quite different. Criticisms such as this one, however, do not detract much from the great merits of this book. The text is written in a clear style and in such a way that it is easy to understand by readers not specialized in chemistry or biochemistry; the relevant background information is outlined in simple terms. Although this might easily lead to a somewhat superficial treatment, the author as a rule has been able to avoid this danger. This book can be highly recommended to all scientists interested in pesticides. J. DEKKER