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Herbicide resistance in plants: biology and biochemistry
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rq
c
ELSEVIER
Agriculture Ecosystems & Envmronment Agriculture, Ecosystemsand Environment63 (1997) 73-78
Book reviews
Herticide resistance in plants Herbicide resistance in plants: biology and biochemistry, edited by S.B. Powles and J.A.M. Holtum, Lewis Press, Boca Raton, FL, USA, 1994, 352 pp., ISBN 0-87371-713-9. This is a long overdue book, needed and fulfilling most of the needs of interested parties. The previous book on the subject (Herbicide Resistance in Plants, 1982, Edited by H.M. LeBaron and J. Gressel, Wiley, New York, 401 pp.) is long out of print, and in most ways, out of date. The earlier work was written when there were less than a half a million hectares of triazine-resistant weeds in Europe, and small patches of that and other resistances throughout the world. Now there are an estimated 6M ha of triazine-resistant weeds and millions of hectares of others, some even appearing after this book was written (extensive areas of isoproturon-resistant Phalaris minor in India and sizable areas of butalchor and propanil-resistant Echinochloas in China and Latin America, respectively). The editors chose a new cadre of authors; of the 20 co-authors of the 12 chapters in this book, only one, then a graduate student, was a co-author in the previous work. The book begins with a brief preface and a picture of the editors together in football regalia. Perhaps they spent too much time in the stadium, as one gets the feeling that the book was under-edited, from the non-uniform terminology, and from the poor proofreading of the text and index. To some of their authors resistance " e v o l v e s " , to others it "develops", even though the appearance of resistant populations is hardly a "developmental" process.
The editors did not keep authors in line in that respect or in the use of ISO common names for herbicides (e.g. chlorotoluron, glufosinate and chloridazon appear as chlortluron, phosphinothricin and pyrazon, without cross-references). This will be hard for neophytes. The first chapter deals with the population dynamics of the evolution of resistant populations. The authors chose to use May and Dobson's model developed for insecticide resistance instead of earlier models for weeds. This model better deals with the genetics of resistance, instead of resistance frequency, but ignores seedbank dynamics, which epidemiologically seems very important; resistance evolves more quickly in no-till situations where seeds are not incorporated into the seedbank than in tillage systems. The chapter authors are probably wrong in assuming that implements are not major movers of resistant seed within a field; gene flow through pollen cannot explain the spread of maternally inherited triazine resistance within fields. The senior editor has presented data on how modifying combines reduces the movement of resistant Lolium rigidum within fields. Still, there are lots of basics to be learned from this chapter, even if it is weak in explaining how the basics are applicable. No one yet has a good explanation of why crop and herbicide rotations delay resistance better than all models predict. Most of the rest of the book is divided into resistance by herbicide groups. This precludes any author asking or answering the question about why there are at most rare cases of resistance to certain herbicides, used more often than some where resistance has evolved, e.g. chloroacetamides, protox in-
74
Book reviews
hibitors, carbamate and thiocarbamate herbicides, dalapon and many others, mainly older compounds. The well-written chapter on resistance to photosystem II herbicides has little to update on the previously well-covered target site other than the molecular biology; but why weeds have mostly evolved one amino acid transversion (Ser264 to Gly264) while many other mutational sites are known from laboratory selections, was not addressed. There is a good description of metabolic resistance to three photosystem II herbicides. The chapter on resistance to photosystem I herbicides is a rather valuable compendium of the findings of various groups. Unfortunately, it did not separate the resistant weeds into two groups on the basis of those that die back and regenerate versus those where treated leaves themselves are resistant. This might have helped the uninitiated to better understand the mechanisms that might be involved. It is also too bad that the author perpetrates a previously published mistake, e.g. that morphamquat (sic) is a photosystem I inhibitor, a statement for which there seems to be no evidence. The chapter on resistance to acetolactate synthase inhibitors is the epitome of how a chapter should be written. It contains an excellent and critical summary of the data, presents unexplained anomalies, has a better explanation of the field population dynamics than the first chapter. It also contains some important, original epidemiological data on 300 biotype cross-resistances, put in easy to follow figures. This is by far, the best chapter in the book, veering back and forth from basics to field. The chapter on resistance to acetyl CoA carboxylase-inhibiting herbicides is a generally excellent compendium of much of the published data. It did miss the seminal research by Heap showing that the actual level of resistance within Lolium populations was a direct function of the number of repeated treatments. In describing the lack of data for metabolic resistance, it would have been useful had the authors re-evaluated t h e editors own research showing 5 - 1 0 % greater rate of metabolism in resistant Lolium. Would that allow resistance to such slow killing herbicides? The. chapter on resistance to auxin analog herbicides is split into two parts; the larger part deals with auxins actions and their selectivity in crops, and a
much shorter, more perfunctory section of the weeds that have evolved resistance. The author cites the finding of 2,4-D-resistant wild carrots decades ago and repeats the claim that 1% of the population was resistant. He does not question why it was never again found, despite the high frequency. No seed was ever made available of this material. A longer section appears on transgenic crops bearing auxin resistance via degradation. The well-balanced chapter on glyphosate resistance gives a good description of how glyphosate-resistant crops were engineered. It also describes the many oft-ignored cases of intraspecific genetic variability in responses to glyphosate and provides a prophetic warning that overuse could lead to resistance, as it recently has with Lolium rigidum in Australia. The chapter on cross and multiple resistances departs from the commonly used definitions based on epidemiology (single compound use leads to resistance to disparate compounds versus sequential selection and sequential evolution, respectively). Instead they use a mechanistic definition based on the modes of resistance. They then give a good summary of selected findings, but by ignoring epidemiological studies such as Heap's, may have missed a better understanding of underlying principles. The chapter on the genetics of resistance is an excellent, balanced, and critical status summary, as well as a description of anomalies, and where more research is needed. The chapter on fitness well discusses the interacting factors governing this process. It fails to go on to say that most papers claiming to measure fitness have not measured some of the critical factors involved, nor do they discuss how this can lead to erroneous conclusions. The chapter on management of resistant weed populations seems to bear a fatalistic approach, i.e. that one can deal with resistance only after it covers large areas; the author presumes that farmers will not use pre-emptive strategies. This chapter does have many insights into how to deal with resistance after the fact. The book has a pretty good index, although there are far too many misspelled entries and a few inscrutable ones (e.g. both with alachlor and flurmeturon (sic) we are told to "see also dinitroaniline
Book reviews
herbicides". Neither alachlor nor fluometuron are dinitroanilines, nor is their a clue under the dinitroaniline entry why we are to see it. This reviewer has pointed out the many and often annoying shortcomings of this important book. The book contains the best update available, and the reviewer's comments are meant only to tell the reader to be highly critical upon reading, use this as any text as a lead to the original literature, which must be read critically. This book should be on the desk of every researcher and student, in academia, extension, regulation, and industry dealing with herbicides. Wisely used and well interpreted, it can assist both in dealing pre-emptively with resistance as well as after the fact. It is an excellent summary up to 1993... but much has happened since, so a revised edition would already be useful. Jonathan Gressel
Plant Genetics Weizmann Institute of Science Rehovot 766100 Israel
Environmental heritage of Soviet agriculture The environmental heritage of Soviet agriculture, by Bo Libert, CAB International, Oxon, UK, 228 pp., price £40.00 (US$72.50 Americas only), ISBN 0851989616. The idea for writing this book came to the author while he was serving as an agricultural counselor at the Swedish Embassy in Moscow at the end of the 1980s. During the height of perestroika and glasnost, evidence of environmental degradation was appearing almost daily. The author's objective is to give an overall view of the interrelationship between agriculture and the environment in the states of the former USSR. The primary topics covered are land, soil humus, nutrients, water and irrigation, pesticides, and industrial and radiation pollution. As in most countries, water and wind erosion are serious problems in Soviet and post-Soviet agriculture. Annual losses of grains caused by erosion are estimated to be approximately 10%. In annual row
75
crops the average loss of soil is 30 t / h a / y e a r in rainfed agriculture and higher than this on some irrigated lands. This loss greatly exceeds the soil formation rate which is 0.5 to 1 t / h a / y e a r . Although this is a significant soil loss and clearly one of concern, worldwide soil losses of 30 t / h a / y e a r on cropland by erosion are common (Pimentel et al., 1995). Most wind erosion in Soviet agriculture occurs on pasture lands where overgrazing by livestock is common. In 1986, 1.5 million sheep grazed the 3.6 million ha of pastures. This sheep density was twice the sustainable level and serious pasture damage was estimated to be 75%. This damage level is high but, again, overgrazing and pasture damage is common throughout the world (Pimentel, D., Harvey, C., Resosudarmo, P., Sinclair, K., Kurz, D., McNair, M., Crist, S., Sphpritz, L., Fitton, L., Saffouri, R. and Blair, R., 1995. Environmental and economic costs of soil erosion and conservation benefits. Science, 267: 1117-1123). In addition to loss of soil depth, erosion reduces soil humus, water-holding capacity, nutrients, soil biota and increases the rate of water runoff. Soil humus is selectively removed by both water and wind erosion because it is light in weight. The loss of soil humus in turn reduces the soil water-holding capacity, soil nutrients, and soil biota which are all essential for a productive soil. Studies in Uzbekistan have demonstrated that reducing the soil humus level from 1.43% to 0.92% reduced grain yields by about 50%. Also, in parts of Rosto oblast it was reported that reducing soil humus from 500 to 250 t / h a reduced grain yields by about 70% during dry years. Although reduced soil water and biota are related to these reduced grain yields, loss of nutrients is also of major importance. The estimate is that soil erosion accounts for an annual loss of 5.4 million tonnes of nitrogen and 1.8 million tonnes of phosphorus. Erosion and soil loss are common due to water and wind on irrigated land but water losses and shortages for irrigation are equally serious problems. In the former USSR, the percentage of water resources used for irrigation from rivers ranged from 5% to 88%. Rivers that were drawn down by 80% or more were left with only a trickle of water and the natural fauna and flora mostly disappeared. The
rq
c
ELSEVIER
Agriculture Ecosystems & Envmronment Agriculture, Ecosystemsand Environment63 (1997) 73-78
Book reviews
Herticide resistance in plants Herbicide resistance in plants: biology and biochemistry, edited by S.B. Powles and J.A.M. Holtum, Lewis Press, Boca Raton, FL, USA, 1994, 352 pp., ISBN 0-87371-713-9. This is a long overdue book, needed and fulfilling most of the needs of interested parties. The previous book on the subject (Herbicide Resistance in Plants, 1982, Edited by H.M. LeBaron and J. Gressel, Wiley, New York, 401 pp.) is long out of print, and in most ways, out of date. The earlier work was written when there were less than a half a million hectares of triazine-resistant weeds in Europe, and small patches of that and other resistances throughout the world. Now there are an estimated 6M ha of triazine-resistant weeds and millions of hectares of others, some even appearing after this book was written (extensive areas of isoproturon-resistant Phalaris minor in India and sizable areas of butalchor and propanil-resistant Echinochloas in China and Latin America, respectively). The editors chose a new cadre of authors; of the 20 co-authors of the 12 chapters in this book, only one, then a graduate student, was a co-author in the previous work. The book begins with a brief preface and a picture of the editors together in football regalia. Perhaps they spent too much time in the stadium, as one gets the feeling that the book was under-edited, from the non-uniform terminology, and from the poor proofreading of the text and index. To some of their authors resistance " e v o l v e s " , to others it "develops", even though the appearance of resistant populations is hardly a "developmental" process.
The editors did not keep authors in line in that respect or in the use of ISO common names for herbicides (e.g. chlorotoluron, glufosinate and chloridazon appear as chlortluron, phosphinothricin and pyrazon, without cross-references). This will be hard for neophytes. The first chapter deals with the population dynamics of the evolution of resistant populations. The authors chose to use May and Dobson's model developed for insecticide resistance instead of earlier models for weeds. This model better deals with the genetics of resistance, instead of resistance frequency, but ignores seedbank dynamics, which epidemiologically seems very important; resistance evolves more quickly in no-till situations where seeds are not incorporated into the seedbank than in tillage systems. The chapter authors are probably wrong in assuming that implements are not major movers of resistant seed within a field; gene flow through pollen cannot explain the spread of maternally inherited triazine resistance within fields. The senior editor has presented data on how modifying combines reduces the movement of resistant Lolium rigidum within fields. Still, there are lots of basics to be learned from this chapter, even if it is weak in explaining how the basics are applicable. No one yet has a good explanation of why crop and herbicide rotations delay resistance better than all models predict. Most of the rest of the book is divided into resistance by herbicide groups. This precludes any author asking or answering the question about why there are at most rare cases of resistance to certain herbicides, used more often than some where resistance has evolved, e.g. chloroacetamides, protox in-
74
Book reviews
hibitors, carbamate and thiocarbamate herbicides, dalapon and many others, mainly older compounds. The well-written chapter on resistance to photosystem II herbicides has little to update on the previously well-covered target site other than the molecular biology; but why weeds have mostly evolved one amino acid transversion (Ser264 to Gly264) while many other mutational sites are known from laboratory selections, was not addressed. There is a good description of metabolic resistance to three photosystem II herbicides. The chapter on resistance to photosystem I herbicides is a rather valuable compendium of the findings of various groups. Unfortunately, it did not separate the resistant weeds into two groups on the basis of those that die back and regenerate versus those where treated leaves themselves are resistant. This might have helped the uninitiated to better understand the mechanisms that might be involved. It is also too bad that the author perpetrates a previously published mistake, e.g. that morphamquat (sic) is a photosystem I inhibitor, a statement for which there seems to be no evidence. The chapter on resistance to acetolactate synthase inhibitors is the epitome of how a chapter should be written. It contains an excellent and critical summary of the data, presents unexplained anomalies, has a better explanation of the field population dynamics than the first chapter. It also contains some important, original epidemiological data on 300 biotype cross-resistances, put in easy to follow figures. This is by far, the best chapter in the book, veering back and forth from basics to field. The chapter on resistance to acetyl CoA carboxylase-inhibiting herbicides is a generally excellent compendium of much of the published data. It did miss the seminal research by Heap showing that the actual level of resistance within Lolium populations was a direct function of the number of repeated treatments. In describing the lack of data for metabolic resistance, it would have been useful had the authors re-evaluated t h e editors own research showing 5 - 1 0 % greater rate of metabolism in resistant Lolium. Would that allow resistance to such slow killing herbicides? The. chapter on resistance to auxin analog herbicides is split into two parts; the larger part deals with auxins actions and their selectivity in crops, and a
much shorter, more perfunctory section of the weeds that have evolved resistance. The author cites the finding of 2,4-D-resistant wild carrots decades ago and repeats the claim that 1% of the population was resistant. He does not question why it was never again found, despite the high frequency. No seed was ever made available of this material. A longer section appears on transgenic crops bearing auxin resistance via degradation. The well-balanced chapter on glyphosate resistance gives a good description of how glyphosate-resistant crops were engineered. It also describes the many oft-ignored cases of intraspecific genetic variability in responses to glyphosate and provides a prophetic warning that overuse could lead to resistance, as it recently has with Lolium rigidum in Australia. The chapter on cross and multiple resistances departs from the commonly used definitions based on epidemiology (single compound use leads to resistance to disparate compounds versus sequential selection and sequential evolution, respectively). Instead they use a mechanistic definition based on the modes of resistance. They then give a good summary of selected findings, but by ignoring epidemiological studies such as Heap's, may have missed a better understanding of underlying principles. The chapter on the genetics of resistance is an excellent, balanced, and critical status summary, as well as a description of anomalies, and where more research is needed. The chapter on fitness well discusses the interacting factors governing this process. It fails to go on to say that most papers claiming to measure fitness have not measured some of the critical factors involved, nor do they discuss how this can lead to erroneous conclusions. The chapter on management of resistant weed populations seems to bear a fatalistic approach, i.e. that one can deal with resistance only after it covers large areas; the author presumes that farmers will not use pre-emptive strategies. This chapter does have many insights into how to deal with resistance after the fact. The book has a pretty good index, although there are far too many misspelled entries and a few inscrutable ones (e.g. both with alachlor and flurmeturon (sic) we are told to "see also dinitroaniline
Book reviews
herbicides". Neither alachlor nor fluometuron are dinitroanilines, nor is their a clue under the dinitroaniline entry why we are to see it. This reviewer has pointed out the many and often annoying shortcomings of this important book. The book contains the best update available, and the reviewer's comments are meant only to tell the reader to be highly critical upon reading, use this as any text as a lead to the original literature, which must be read critically. This book should be on the desk of every researcher and student, in academia, extension, regulation, and industry dealing with herbicides. Wisely used and well interpreted, it can assist both in dealing pre-emptively with resistance as well as after the fact. It is an excellent summary up to 1993... but much has happened since, so a revised edition would already be useful. Jonathan Gressel
Plant Genetics Weizmann Institute of Science Rehovot 766100 Israel
Environmental heritage of Soviet agriculture The environmental heritage of Soviet agriculture, by Bo Libert, CAB International, Oxon, UK, 228 pp., price £40.00 (US$72.50 Americas only), ISBN 0851989616. The idea for writing this book came to the author while he was serving as an agricultural counselor at the Swedish Embassy in Moscow at the end of the 1980s. During the height of perestroika and glasnost, evidence of environmental degradation was appearing almost daily. The author's objective is to give an overall view of the interrelationship between agriculture and the environment in the states of the former USSR. The primary topics covered are land, soil humus, nutrients, water and irrigation, pesticides, and industrial and radiation pollution. As in most countries, water and wind erosion are serious problems in Soviet and post-Soviet agriculture. Annual losses of grains caused by erosion are estimated to be approximately 10%. In annual row
75
crops the average loss of soil is 30 t / h a / y e a r in rainfed agriculture and higher than this on some irrigated lands. This loss greatly exceeds the soil formation rate which is 0.5 to 1 t / h a / y e a r . Although this is a significant soil loss and clearly one of concern, worldwide soil losses of 30 t / h a / y e a r on cropland by erosion are common (Pimentel et al., 1995). Most wind erosion in Soviet agriculture occurs on pasture lands where overgrazing by livestock is common. In 1986, 1.5 million sheep grazed the 3.6 million ha of pastures. This sheep density was twice the sustainable level and serious pasture damage was estimated to be 75%. This damage level is high but, again, overgrazing and pasture damage is common throughout the world (Pimentel, D., Harvey, C., Resosudarmo, P., Sinclair, K., Kurz, D., McNair, M., Crist, S., Sphpritz, L., Fitton, L., Saffouri, R. and Blair, R., 1995. Environmental and economic costs of soil erosion and conservation benefits. Science, 267: 1117-1123). In addition to loss of soil depth, erosion reduces soil humus, water-holding capacity, nutrients, soil biota and increases the rate of water runoff. Soil humus is selectively removed by both water and wind erosion because it is light in weight. The loss of soil humus in turn reduces the soil water-holding capacity, soil nutrients, and soil biota which are all essential for a productive soil. Studies in Uzbekistan have demonstrated that reducing the soil humus level from 1.43% to 0.92% reduced grain yields by about 50%. Also, in parts of Rosto oblast it was reported that reducing soil humus from 500 to 250 t / h a reduced grain yields by about 70% during dry years. Although reduced soil water and biota are related to these reduced grain yields, loss of nutrients is also of major importance. The estimate is that soil erosion accounts for an annual loss of 5.4 million tonnes of nitrogen and 1.8 million tonnes of phosphorus. Erosion and soil loss are common due to water and wind on irrigated land but water losses and shortages for irrigation are equally serious problems. In the former USSR, the percentage of water resources used for irrigation from rivers ranged from 5% to 88%. Rivers that were drawn down by 80% or more were left with only a trickle of water and the natural fauna and flora mostly disappeared. The