Synthetic pesticides have played a major role in crop protection against the increasing number of pests (insects, nematodes, weeds) and pathogens (fungi, bacteria) related to the intensification of agricultural systems throughout the past decades. In the recent years, environmental side effects and health concerns raised by indiscriminate use have led the EU to the ban of many synthetic carbamate, organophosphate, and organophthalide pesticides (Council Directive 91/414/EEC) and severe evaluation of many others (Regulation 2009/1107/EC and Directive 2009/128/EC). As a result of this drastic revision, currently there is a dramatic lack of commercial products available for crop protection and, therefore, a strong need for new and alternative pest control methods. An interesting source of biorational pesticides may be represented by the biocidal compounds naturally occurring in plants as constituents of the secondary metabolism playing an important role in plant defence mechanisms. The huge applicative potential of plant-derived biocidal compounds is still largely unexploited, if considering that less than 4% of plant secundary metabolites estimated as present in nature has been chemically characterized. Development of botanical pesticides can be based on ethnobotanical studies on traditional uses of plants and extracts for cattle and crop protection, followed by identification of the active molecules or can be derived from systematic screening of botanical families followed by biological tests aimed to discover the active molecules. Groups of plant secundary metabolites most promising for the development of pesticidal formulations are glucosinolates, triterpenoids saponins and more generally triterpenoids, and essential oil and their constituents. Glucosinolates are thioglucosidic secondary metabolites occurring mainly in the Brassicaceae and, at a less extent, in Capparidaceae families. Myrosinase enzyme-catalyzed hydrolysis of glucosinolates following to the incorporation of glucosinolate-containing plant material into the soil results in degradation products (isothiocyanates, thiocyanates, indoles etc.) highly toxic to soilborne pest, pathogens and weeds. This practice, known as biofumigation, may be considered an ecological alternative to soil toxic fumigants such as MeBr, used in the past to suppress soil fungus, bacteria, nematodes and weeds. Plant-derived saponins are triterpene glycosides present in top and root tissues of plant species of the families Leguminosae, Alliaceae, Asteraceae, Polygalaceae and Agavaceae, as well as in the bark of the tree species Quillaja saponaria (Quillajaceae). Chemical, physical and physiological characteristics of naturally occurring saponins provide them with a broad spectrum of biological effects, among which also significant antifeedant, fungicidal and nematicidal properties. Essential oils are volatile, natural, heterogeneous mixtures of single substances, mainly terpenes, terpenoids and other aromatic and aliphatic constituents, formed as secundary metabolites by aromatic plants belonging to a number of botanical families, like Lamiaceae, Myrtaceae, Lauraceae, Asteraceae. Due to their great number of constituents, essential oils are able to affect several targets at the same time, thus decreasing the target organisms' resistance or adaptation. Biological activities of EOs and their components are extended to a broad spectrum of insects, nematodes, fungal pathogens and weeds, through different mechanisms of action, such as behaviour and feeding detterance effects, fumigant toxicity, knockdown activity and contact lethal toxicity. Among terpenes, limonoid triterpenes have been demonstrated to possess interesting insecticidal, nematicidal and antifungal properties. Occurrence of these compounds is mainly limited to plant families of the families Meliaceae and Rutaceae. Most work on limonoids has been focused on azadirachtin, a tetranortriterpenoid present in the species Azadirachta indica and used for the production of a wide range of commercial formulations exhibiting good efficacy against a huge number of insect species, mites and nematodes. Alkaloids, phenolics, cyanogenic glucosides, polyacetylenes and polythienyls are further groups of secundary metabolites also known for a biocidal activity and susceptible for the production of natural pesticides. Alkaloids are derived from various botanical families, amongst which the Solacaneae, and include a number of molecules, such as nicotine, veratrine, cevatrine and ryanodine, used as insecticides since many years. Phenolics were found also toxic to insects, fungi, bacteria, nematodes and weeds. Feeding attractant and deterrent properties on insects have been reported also for flavonoids, a major class of phenolic compounds including rotenone, with the alkaloid nicotine one of the first insecticides used all over the world. Cyanogenic glucosides are amino acid-derived secundary metabolites releasing, upon tissue disruption, hydrogen cyanide that suppress insects, fungus, nematodes and weeds. Finally, polyacetylenes and polythienyls are substances present in Tagetes species well known for their insecticidal and nematicidal properties.
Biocide plants as a sustainable tool for the control of crop pests and pathogens
Trifone D'Addabbo;
2014
Abstract
Synthetic pesticides have played a major role in crop protection against the increasing number of pests (insects, nematodes, weeds) and pathogens (fungi, bacteria) related to the intensification of agricultural systems throughout the past decades. In the recent years, environmental side effects and health concerns raised by indiscriminate use have led the EU to the ban of many synthetic carbamate, organophosphate, and organophthalide pesticides (Council Directive 91/414/EEC) and severe evaluation of many others (Regulation 2009/1107/EC and Directive 2009/128/EC). As a result of this drastic revision, currently there is a dramatic lack of commercial products available for crop protection and, therefore, a strong need for new and alternative pest control methods. An interesting source of biorational pesticides may be represented by the biocidal compounds naturally occurring in plants as constituents of the secondary metabolism playing an important role in plant defence mechanisms. The huge applicative potential of plant-derived biocidal compounds is still largely unexploited, if considering that less than 4% of plant secundary metabolites estimated as present in nature has been chemically characterized. Development of botanical pesticides can be based on ethnobotanical studies on traditional uses of plants and extracts for cattle and crop protection, followed by identification of the active molecules or can be derived from systematic screening of botanical families followed by biological tests aimed to discover the active molecules. Groups of plant secundary metabolites most promising for the development of pesticidal formulations are glucosinolates, triterpenoids saponins and more generally triterpenoids, and essential oil and their constituents. Glucosinolates are thioglucosidic secondary metabolites occurring mainly in the Brassicaceae and, at a less extent, in Capparidaceae families. Myrosinase enzyme-catalyzed hydrolysis of glucosinolates following to the incorporation of glucosinolate-containing plant material into the soil results in degradation products (isothiocyanates, thiocyanates, indoles etc.) highly toxic to soilborne pest, pathogens and weeds. This practice, known as biofumigation, may be considered an ecological alternative to soil toxic fumigants such as MeBr, used in the past to suppress soil fungus, bacteria, nematodes and weeds. Plant-derived saponins are triterpene glycosides present in top and root tissues of plant species of the families Leguminosae, Alliaceae, Asteraceae, Polygalaceae and Agavaceae, as well as in the bark of the tree species Quillaja saponaria (Quillajaceae). Chemical, physical and physiological characteristics of naturally occurring saponins provide them with a broad spectrum of biological effects, among which also significant antifeedant, fungicidal and nematicidal properties. Essential oils are volatile, natural, heterogeneous mixtures of single substances, mainly terpenes, terpenoids and other aromatic and aliphatic constituents, formed as secundary metabolites by aromatic plants belonging to a number of botanical families, like Lamiaceae, Myrtaceae, Lauraceae, Asteraceae. Due to their great number of constituents, essential oils are able to affect several targets at the same time, thus decreasing the target organisms' resistance or adaptation. Biological activities of EOs and their components are extended to a broad spectrum of insects, nematodes, fungal pathogens and weeds, through different mechanisms of action, such as behaviour and feeding detterance effects, fumigant toxicity, knockdown activity and contact lethal toxicity. Among terpenes, limonoid triterpenes have been demonstrated to possess interesting insecticidal, nematicidal and antifungal properties. Occurrence of these compounds is mainly limited to plant families of the families Meliaceae and Rutaceae. Most work on limonoids has been focused on azadirachtin, a tetranortriterpenoid present in the species Azadirachta indica and used for the production of a wide range of commercial formulations exhibiting good efficacy against a huge number of insect species, mites and nematodes. Alkaloids, phenolics, cyanogenic glucosides, polyacetylenes and polythienyls are further groups of secundary metabolites also known for a biocidal activity and susceptible for the production of natural pesticides. Alkaloids are derived from various botanical families, amongst which the Solacaneae, and include a number of molecules, such as nicotine, veratrine, cevatrine and ryanodine, used as insecticides since many years. Phenolics were found also toxic to insects, fungi, bacteria, nematodes and weeds. Feeding attractant and deterrent properties on insects have been reported also for flavonoids, a major class of phenolic compounds including rotenone, with the alkaloid nicotine one of the first insecticides used all over the world. Cyanogenic glucosides are amino acid-derived secundary metabolites releasing, upon tissue disruption, hydrogen cyanide that suppress insects, fungus, nematodes and weeds. Finally, polyacetylenes and polythienyls are substances present in Tagetes species well known for their insecticidal and nematicidal properties.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
