Natural products in crop protection

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Abstract

The tremendous increase in crop yields associated with the ‘green’ revolution has been possible in part by the discovery and utilization of chemicals for pest control. However, concerns over the potential impact of pesticides on human health and the environment has led to the introduction of new pesticide registration procedures, such as the Food Quality Protection Act in the United States. These new regulations have reduced the number of synthetic pesticides available in agriculture. Therefore, the current paradigm of relying almost exclusively on chemicals for pest control may need to be reconsidered. New pesticides, including natural product-based pesticides are being discovered and developed to replace the compounds lost due to the new registration requirements. This review covers the historical use of natural products in agricultural practices, the impact of natural products on the development of new pesticides, and the future prospects for natural products-based pest management.

Graphical abstract

This review covers the historical and current use of natural products for pest management in agriculture.

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Introduction

The success of modern agricultural practices is due in part to discovery and adoption of chemicals for pest control. Indeed, the tremendous increase in crop yields associated with the ‘green’ revolution would not have been achieved without the contribution of these synthetic compounds. The abundance of high quality food in developed nations has all but eliminated concerns about access to food in these countries. However, concerns over the potential impact of pesticides on the environment has now become more pressing and more stringent pesticide registration procedures, such as the Food Quality Protection Act in the United States,1 have been introduced. These new regulations have reduced the number of synthetic pesticides available in agriculture. Therefore, the current paradigm of relying almost exclusively on chemicals for pest control may need to be reconsidered.2

New pesticides, including natural product-based pesticides are being discovered and developed to replace the compounds lost due to the new registration requirements.3 New pesticides are also needed to combat the evolution of resistance to pesticides.3 This review covers the historical use of natural products in agricultural practices, the impact of natural products on the development of new pesticides, and the future prospects for natural products-based pest management. We separate products or compounds that might be used in organic agriculture from those used in conventional agriculture, but make the disclaimer that not every product that we mention in the organic agriculture sections may be legally used in every country for organic agriculture. The rules regarding what is accepted for organic agriculture vary between countries and even between states and do not always have a scientific rational for inclusion or exclusion.4, 5 In general, organic agriculture does not accept synthetic versions of natural compounds. Organic farmers need to consult with their certification agency or program to be sure that any material they use is ‘certified’ or acceptable as organic. Also, we do not cover biocontrol products (living organisms) for pest management, many of which are used by organic farmers. For the most part, we do not mention natural products that are not currently used in agriculture for pest management. Many natural compounds have been discovered and patented for such use, but are not commercially available for numerous reasons.

The need for producing more food within a particular area arose as nomadic populations of hunter-gatherers settled to form more permanent communities. For thousands of years, agricultural practices relied heavily on crop rotation or mixed crop planting to optimize natural pest control (such as predation, parasitism, and competition). Therefore, the concept of ‘natural pesticides’ arose early in the development of agriculture. Indeed, the Lithica poem (c. 400 B.C.) states ‘All the pests that out of earth arise, the earth itself the antidote supplies’.6 Greek and Roman scholars such as Theophrastus (371–287 B.C.), Cato the Censor (234–149 B.C.), Varro (116–27 B.C.), Vergil (70–19 B.C.), Columella (4–70 A.D.) and Pliny the elder (23–79 A.D.) published treaties on agricultural practices to minimize the negative effects of pests on crops. Methods such as mulching and burning, as well as the use of oils for pest control were mentioned. Chinese literature (ca. 300 A.D.) describes an elaborate system of biological control of caterpillar infestations in citrus orchards. Colonies of the predatory ants (Oecophylla smaragdina) were introduced in citrus groves, and bridges made of bamboo allowed the ants to move between trees. A survey of the Shengnong Ben Tsao Jing era (25–220 A.D.) shows that 267 plant species were known to have pesticidal activity.7 Finally, the use of beneficial insects to control other insect pests was mentioned by Linnaeus as early as 1752, and he won a prize in 1763 for an essay describing the biological control of caterpillars.

The European agricultural revolution that followed in the 19th century was accompanied by more extensive and international trade that resulted in the discovery of botanical insecticidal powders from Chrysanthemum flower heads and Derris root which contain pyrethrum and rotenone, respectively. The advent of extensive monoculture and intensive agricultural practices of the 20th century was accompanied by increases in yields. New cultivars were selected based on their higher yields, but many of these lines seem to have lower resistance to pests. This has resulted in greater pest pressure, which has mostly been addressed by the use of synthetic pesticides.

A recent report probing the structural diversity of organic chemistry by performing a scaffold analysis of all the compounds available in the CAS registry confirmed that most of the 24 million organic compounds in the database can be classified in as few as 143 basic structural groups.8 This is due primarily to the fact that molecular scaffoldings used in organic chemistry are limited. On the other hand, a study on the complementarity between synthetic and natural pharmacophores highlighted that natural products generally have a high structural diversity, possessing more chiral centers, sp3-hybridized carbons, and rings than synthetic compounds.9 Few natural products contain halogens (Cl, F, and Br), but they tend to be rich in oxygen and nitrogen, and may contain sulfate or phosphate groups. This diversity may serve as useful novel scaffoldings in developing new classes of natural product-based pesticides.10, 11, 12 Therefore, new cheminformatic and synthetic techniques have been developed to identify and design compounds with natural product-like properties.13, 14, 15

The complexity of the carbon skeleton of natural products is the result of a natural ‘high-throughput’ screen to select compounds with appropriate biologically activities. The term ‘high-throughput’ does not refer to the speed of the selection, but rather to the innumerable permutations of relatively complex structures that have been synthesized by a very large number of biochemical machines (organisms) over an extremely long time. Furthermore, since these products are almost exclusively derived from pathways associated with secondary metabolism, these compounds have a high likelihood to possess some biological activity against other organisms, often via novel mechanisms of action,2, 16, 17 which is particularly important since new modes of action are so deeply needed as pests continue to evolve resistance to the compounds currently available.

An important benefit of natural product-based pesticides is their relatively short environmental half-lives, which is due to the fact that they do not possess ‘unnatural’ ring structures and contain relatively few halogen substituents. While these compounds are perceived to be environmentally benign, very little is known about the fate of natural products in the environment.18

Section snippets

Natural products for weed management

The management of weeds has been a major problem since the inception of agriculture. In fact, unmanaged weeds cause greater reduction in crop yields than the presence of any other agricultural pest. Manual labor in ancestral farming practice is expended mostly on hand weeding of fields. Not surprisingly, modern agriculture relies heavily on the use of synthetic herbicides for managing weeds. This has been possible because synthetic herbicides are highly effective (active ingredient application

Natural products for insect management

One of the more noticeable trends in pesticide sales over the past 25 years is the increasing market share of herbicides relative to other pesticides. In 2004, herbicides accounted for 45.4% of the agrochemical market, followed by insecticides 27.5%, fungicides 21.7% and other products 5.4%.95

Recent reports indicate that the use of natural product and natural product-derived insecticides continue to increase, whereas sales of organophosphates are declining. Indeed, three out of the five most

Natural products for plant pathogen management

Natural products for plant pathogen management have been the topic of or included in several previous reviews.135, 136, 137 Many natural compounds and preparations have been described with activity against bacterial or fungal plant pathogens. Indeed, plants protect themselves from microbial attacks with both constitutive antimicrobials and compounds induced by the attacking pathogen (phytoalexins). Phytoalexins have not been directly exploited as fungicides, but natural products have been used

Conclusions

Conventional pest management has been significantly influenced by bioactive natural products that are used directly, or in a derived form, as pesticides. Biobased pesticides are commonly used as alternatives to synthetic compounds in organic agriculture. While some of these insecticidal and fungicidal compounds have transferred successfully in the more conventional crop production systems, good natural herbicides have been lacking. The only natural herbicide available for large-scale cropping

References and notes (164)

  • A.L. Harvey

    Curr. Opin. Chem. Biol.

    (2007)
  • D.L. Liu et al.

    J. Plant Growth Regul.

    (1994)
  • B. Lederer et al.

    Pestic. Biochem. Physiol.

    (2004)
  • M.Y. Fukuda et al.

    Pestic. Biochem. Physiol.

    (2004)
  • M.H. Douglas et al.

    Phytochemistry

    (2004)
  • F.E. Dayan et al.

    Phytochemistry

    (2007)
  • H. Kato-Noguchi

    J. Plant Physiol.

    (2004)
  • H. Kato-Noguchi et al.

    Phytochemistry

    (2003)
  • G. Meazza et al.

    Phytochemistry

    (2002)
  • I.S. Fomsgaard et al.

    Chemosphere

    (2004)
  • House Resolution-1627 Food Quality Protection Act (FQPA) of 1996....
  • F.E. Dayan et al.

    Pestic. Outlook

    (1999)
  • L.G. Copping et al.

    Pest Manage. Sci.

    (2007)
  • USEPA. http://www.epa.gov/oecaagct/torg.html#Guidance%20for%20Labeling, accessed August,...
  • International Federation of Organic Agriculture Movements. http://www.ifoam.org/organic_facts/harmonization/index.html,...
  • Ibn, H.; Tyrwhitt, T.; Orpheus, Peri lithôn De lapidibus, poema Orpheo a quibusdam adscriptum. J. Nichols; apud...
  • R.Z. Yang et al.

    Econ. Bot.

    (1988)
  • A.H. Lipkus et al.

    J. Org. Chem.

    (2008)
  • T. Henkel et al.

    Angew. Chem., Int. Ed.

    (1999)
  • L. Costantino et al.

    Curr. Med. Chem.

    (2006)
  • M.A. Koch et al.

    Proc. Natl. Acad. Sci. U.S.A.

    (2005)
  • P. Ertl et al.

    J. Chem. Inf. Model.

    (2008)
  • S.N. Lopez et al.

    Proc. Natl. Acad. Sci. U.S.A.

    (2007)
  • R.J. Quinn et al.

    J. Nat. Prod.

    (2008)
  • F.E. Dayan et al.

    J. Chem. Ecol.

    (2000)
  • S.O. Duke et al.
  • A.L. Gimsing et al.

    Environ. Toxicol. Chem.

    (2006)
  • S.A. Senseman

    Herbicide Handbook

    (2007)
  • Anonymous Organic farming....
  • D.W. Lotter

    J. Sustain. Agric.

    (2003)
  • W. Quarles

    Common Sense Pest Control Quart.

    (1999)
  • M.C. McDade et al.

    Am. J. Altern. Agric.

    (2000)
  • Christians, N. E. U.S. Patent No. 5,030,268,...
  • R.E. Gough et al.

    Hortscience

    (1999)
  • D.L. Liu et al.

    Hortscience

    (1997)
  • J.B. Unruh et al.

    Crop Sci.

    (1997)
  • D.L. Liu et al.

    J. Plant Growth Regul.

    (1996)
  • S.L. Young

    Weed Technol.

    (2004)
  • H.-P. Malkomes

    J. Plant Dis. Prot.

    (2005)
  • D.F. Spencer et al.

    J. Aquat. Plant Manage.

    (1999)
  • L.W.J. Anderson

    J. Aquat. Plant Manage.

    (2007)
  • H.-P. Malkomes

    Umweltwiss. Schadst. Forsch.

    (2006)
  • P. Poignant

    C.R. Acad. Sci.

    (1954)
  • Anonymous Stockman Grass Farmer 2002, July,...
  • R. Coleman et al.

    Weed Technol.

    (2006)
  • J.C. Fausey

    Horttechnology

    (2003)
  • R. Coleman et al.

    Weed Technol.

    (2008)
  • P. Scarfato et al.

    J. Appl. Polym. Sci.

    (2007)
  • T. Tworkoski

    Weed Sci.

    (2002)
  • J.P. Bouverat-Bernier

    Herb. Gallic

    (1992)
  • Cited by (0)

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