Multicomponent reactions in crop protection chemistry

An overview is given of the significance of multicomponent reactions in the synthesis of agrochemicals. The most important applications of multicomponent condensations, such as the Biginelli reaction, Bucherer-Bergs reaction, Hantzsch dihydropyridine synthesis, Kabachnik-Fields reaction, Mannich reaction, Passerini reaction, Petasis reaction, Strecker reaction, Ugi reaction and Willgerodt-Kindler reaction, to the synthesis of herbicidally, fungicidally and insecticidally active compounds are presented. Also the mode of action and biological activity of these multicomponent reaction products are reported.     

Role of modern chemistry in sustainable arable crop protection

Organic chemistry has been, and for the foreseeable future will remain, vitally important for crop protection. Control of fungal pathogens, insect pests and weeds is crucial to enhanced food provision. As world population continues to grow, it is timely to assess the current situation, anticipate future challenges and consider how new chemistry may help meet those challenges. In future, agriculture will increasingly be expected to provide not only food and feed, but also crops for conversion into renewable fuels and chemical feedstocks. This will further increase the demand for higher crop yields per unit area, requiring chemicals used in crop production to be even more sophisticated. In order to contribute to programmes of integrated crop management, there is a requirement for chemicals to display high specificity, demonstrate benign environmental and toxicological profiles, and be biodegradable. It will also be necessary to improve production of those chemicals, because waste generated by the production process mitigates the overall benefit. Three aspects are considered in this review: advances in the discovery process for new molecules for sustainable crop protection, including tests for environmental and toxicological properties as well as biological activity; advances in synthetic chemistry that may offer efficient and environmentally benign manufacturing processes for modern crop protection chemicals; and issues related to energy use and production through agriculture.     

Natural products in crop protection

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.     

RNAi-mediated crop protection against insects

Downregulation of the expression of specific genes through RNA interference (RNAi), has been widely used for genetic research in insects. The method has relied on the injection of double-stranded RNA (dsRNA), which is not possible for practical applications in crop protection. By contrast, specific suppression of gene expression in nematodes is possible through feeding with dsRNA. This approach was thought to be unfeasible in insects, but recent results have shown that dsRNA fed as a diet component can be effective in downregulating targeted genes. More significantly, expression of dsRNA directed against suitable insect target genes in transgenic plants has been shown to give protection against pests, opening the way for a new generation of insect-resistant crops.     

Environmental impact of adjuvants in crop protection

The overall performance of chemical and biological plant protection products is enhanced by the use of adjuvants in the formulation (formulation adjuvants) or in the spray tank (spray adjuvants). Both types of adjuvants aim to stabilize the formulation, to improve the efficiency of the active ingredients and to reduce application and environmental risks. As an important part of the formulation, both quantitatively and qualitatively, the environmental impact and toxicology of adjuvants can not always be considered as inert. However, little is known of their impact as part of plant protection products compared with the active substances. Therefore an experimental framework is needed as a tool for a consistent environmental legislation.     

Simulation and systems management in crop protection

Book Review

Simulation and systems management in crop protectionR. Rabbinge, S.A. Ward and H.H. van Laar (Eds.), (Simulation Monographs 32). Wageningen, The Netherlands: Centre for Agricultural Publishing and Documentation (Pudoc), 1989, xiv + 420 pages. Dfl. 125.00. ISBN 90-220-0899-1     

Aquatic ecotoxicity for common crop protection aids

Crop protection aids, used in the agriculture phase, contribute a great deal to the environmental impact of food products. An adequate inclusion of those substances in life cycle assessment is usually hampered by the lack of relevant equivalency factors. In this paper rough equivalency factors are given for 65 frequently used herbicides and pesticides. Those factors are calculated according to the methodology, originally developed by EPA, which was used by CML in 1992. It is acknowledged that equivalency factors, derived in this way, have a limited value. They only indicate potential impacts, ignoring the fate of such substances. However, as long as better data are lacking, these figures provide a useful approximation.     

Mefluidide protection of severely chilled crop plants

Mefluidide, the common name of N-(2,4-dimethyl-5-[([trifluoromethyl] sulfonyl)amino]phenyl)acetamide, is capable of protecting chilling sensitive plants such as cucumber (Cucumis sativus L.) and corn (Zea mays L.) from chilling injury. The applied concentrations that protect plants from stress are species specific. Applied above a threshold concentration, it has no protective effect. Regardless of its immediate potential for agriculture, it appears at least to be a powerful tool for the biologist in the study of the protection from temperature stress mechanism.     

Use of natural products in the crop protection industry

Nature is a rich source of compounds exhibiting biological activity against weeds, plant diseases, insects and mites. Many of these natural products have complex structures, insufficient biological activity and low persistence under field conditions. Thus the share of natural products being used as active ingredients per se in today’s crop protection market is relatively small. In some cases the natural products have been further modified to provide semi-synthetic derivatives with improved biological properties. More importantly, natural products served as lead structures inspiring chemists to prepare new synthetic analogues with often improved biological activity, simplified structures, increased safety towards humans and the environment and an optimized persistence. This article is not an extensive review of natural products in crop protection, but it discusses some examples illustrating the use of natural products per se, their use as starting materials to prepare semi-synthetic products, and their use as lead structures to prepare new synthetic products which may in the end bear no resemblance to the initial lead.     

Guttation 1: chemistry, crop husbandry and molecular farming

Guttation is one of the most conspicuous visible phenomena in plants occurring in a wide range of plants. The guttation fluids, though look clear and translucent, carry a number of organic and inorganic constituents. The organic component may include sugars, amino acids, general proteins, antimicrobial phylloplane proteins, transport proteins for transporting sucrose, purine and cytokinins, toxic elements etc. and enzymes such as peroxidases, dehydrogenases, ATPases, in addition to mRNA, ATP, reductants and other important ingredients of plant life. Guttation fluids also contain a number of natural plant hormones such as auxins, gibberellins, cytokinins, abscisic acid etc., apart from several vitamins. Recent discoveries have revealed the presence of a number of salts, ions, nutrients and macromolecules in guttation fluid playing significant role in enhancing disease resistance, tolerance to toxic elements, photosynthetic efficiency, biomass production and economic yield of agricultural crops. In the light of aforementioned discoveries in guttation transgenic plants have been created to serve as bio-factories for producing various kinds of phytochemicals of immense agricultural, pharmaceutical, nutriceutical, therapeutic, cosmeceutic and commercial significance impacting food productivity and human health adding happiness to life.     

Cereal production,crop protection and plant breeding*

Trends in British agriculture which have led to the eclipse of rotations, to the concentration of cereal production on wheat and barley, and to a changeover to winter cereals, have increased the vulnerability of cereal crops to disease. Epidemics have been prevented by the deployment of effective resistances and, more recently, of a wide range of crop protection chemicals. Ecological protection by means of variety mixtures and field diversification has now added a new and effective element for the defence of cereals. The problem of durability of resistances and of the continuing effectiveness of chemicals remains, and new problems of susceptibility of crop varieties to herbicides have arisen. It is possible through the combined use of genetical, chemical and ecological defence mechanisms, to maximise the period of effectiveness of resistance genes and of fungicides and insecticides. The experience of the past half-century has shown that dependence on a single protective mechanism provides only a transient solution to controlling disease.