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Idesia (Arica)

versión On-line ISSN 0718-3429

Idesia vol.38 no.1 Arica mar. 2020 


Secondary plant metabolites and their potential use in the management of agricultural pests in desert Agroecosystems

Tommy Christian Rioja Soto1 

1Faculty of Renewable Natural Resources. Arturo Prat University Iquique, Chile.

In their evolution, plants have developed various defense mechanisms to cope with the effects of stress, both biotic and abiotic. Its phenotypic plasticity and selection pressure have caused a constant chemical fight against herbivores, microorganisms, nematodes, and mites; ikewise, plant defenses have been adapted to continuous abiotic stresses such as drought, salinity, ultraviolet radiation, temperature, floods, and CO 2 concentrations. Therefore, the evolution and micro-evolutions of plants within the defensive context are closely related to the environment that surrounds them.

Although many do not accept the concept, plants "speak" and "inform" the environment of their clinical state, specifically indicating if they are being attacked by insects, mites, nematodes, microorganisms, or affected by some abiotic stress. In this regard, said, "chemical language" occurs through the constitutive production of secondary metabolites, and the subsequent emission of Biogenic Volatile Organic Compounds (BVOCs) into the atmosphere. After the herbivory has occurred, and the detection at the plasma membrane level of molecules present in the saliva of insects and mites (elicitors and effectors), various specific defensive mechanisms are activated at the physiological and genetic level in plants, with influx of Ca + , depolarization of the plasma membrane, oxidations and production of reactive oxygen species, changes in the levels of jasmonic acid (JA), salicylic acid (SA) and ethylene (ET), mainly. Thus, the basal levels of secondary metabolites are increased, and consequently, their emissions change qualitatively and quantitatively. These emissions are renamed Herbivore-Induced Plant Volatiles (HIPVs), which attract natural enemies of pests, such as predators and parasitoids, thus causing tri-trophic interactions in agroecosystems. In this regard, in North America and Europe, slow-release dispensers based on al-lomones and synomones, such as methyl salicylate (MeSA), methyl jasmonate (MeJA) and terpenoids, are used to repel pests and attract natural enemies in organic and clean productions. Therefore, the secondary metabolism of plants presents ideal characteristics for the generation of new techniques and alternative products to broad-spectrum and toxic pesticides for workers, consumers, and the environment.

Generally, plants that grow in desert environments develop additional defenses to mitigate the effects of high temperatures, ultraviolet rays, drought, and salinity. In this regard, there is little information related to these phenomena, which have immeasurable potential to be investigated within the context of innovation and generation of new biotechnology products of natural origin, originating from agroecosystems in northern Chile.

The plant and animal genetic resources, soil micro-fauna, chemical ecology, and ecotypespresent in the valleys and the highlands of the Arica and Parinacota Region have been scarcely investigated; the same has happened in the valleys and oases of the Tarapacá Region. These resources represent a great challenge and opportunity for the study of desert agroecosystems in these regions, which can be classified as actual laboratories with great potential for the development of new strategies and sustainable technologies for the management of agricultural pests in semi-desert areas, and desert of Chile and the world.

Furthermore, climate change and the constant increase in CO 2 concentrations worldwide, which currently exceed 415 parts-per million (ppm), will considerably affect agricultural production, essential for human consumption. In this regard, increases in CO 2 , drought and high temperatures will cause the resetting of trophic interactions between species, the silencing of genes associated with plant defenses (e.g., high concentrations of CO 2 repress the signaling of the phytohormone JA defense), decreased tolerance and resistance of plants (e.g., plants with water stress accumulate JA, affecting the expression of defense genes associated with SA, increasing susceptibility to Hemiptera insects and phytophagous mites), extinction of some plant species, increases in fitness, reproduction and popu lation of arthropod pests due to higher availability of plant biomass (i.g., plants with C3 metabolism increase their biomass in environments rich in CO 2 ), and changes in the production and emission of BVOCs and HIPVs towards the environment.

Therefore, the extreme conditions in northern Chile are ideal for studying the potential scenarios that are visualized in the world agricultural phy-tosanitary field, whose main objective should be the design of new strategies, obtaining new varieties, development of biopesticides based on plant extracts, and devices with synthetic compounds that simulate the defenses of plants, to be incorporated in future programs of holistic and sustainable management of agricultural pests, in arid agroecosystems around the world.

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