Desenvolvimento e Avaliação de Compostos Naturais Eficazes no Controlo Nematodes Parasitas Economicamente Importantes, pela utilização de Fitoquímicos Produzidos a partir de Brássicas e Espécies Produtoras de Óleos Essenciais
Phytophagous nematodes including Globodera (potato cyst nematodes), Heterodera (cereal, soya and beet cyst nematodes), Meloidogyne (root-knot nematodes), and Bursaphelenchus xylophilus (pine nematode, causing pine wilt disease) cause considerable damage and yield losses to common food and fiber plants and other economically-important species in Portugal, Europe, and globally. Currently various synthetic nematicides are used for controlling these pests. Unfortunately many of the most effective chemicals are also highly toxic to humans and animals. Persistent use of these chemicals can lead to accumulation of residues in the soil and in the food plants; causing significant negative health and environmental impacts. In other cases, certain nematicides are being phased out and will soon be unavailable. Due to these greater health risks researchers have begun to look for alternative and more effective natural chemical controls. The phytochemicals (plant secondary metabolites) includes a wide range of chemical structures with diverse biological activities. Common phytochemicals include alkaloids, phenolics, flavonoids, terpenoids, glucosinolates, cyanogenic glycosides, non-protein amino acids (e.g. Allium S-alk(en)yl-L-cysteine sulfoxides) and polythienyls (sulfur-heterocyclic compounds from the plant family Asteraceae). A recent review on the control of nematodes using phytochemicals has listed the most promising candidates. Of the plants identified as sources of potent natural nematicides, those found in the Capparales (glucosinolate-containing) plant order, and species from the family Brassicaceae consistently give good control of nematodes. There is good data from in vitro and in vivo studies on the control of Globodera and Meloidogyne species using crude Brassica and related plant extracts, and more recently for pure compounds such as allylisothiocyanate (derived from singin), 4-methylthiobutyl-isothiocyanate (derived from glucoerucin), benzylisothiocyanate (derived from glucotropaeolin), and 2-phenylethylisothiocyanate (derived from gluconasturtiin). In addition there are recent, important, publications evaluating essential oils derived from different plant species as natural nematicides. Some of these oils have been shown to have significant nematicidal activities against the economically important nematodes. There is also the potential for multipest and pathogen control with these extracts since isothiocyanates and essential oils have been shown to also have potent anti-microbial and anti-fungal activities as well as insecticidal activities. Although there is initial data on phytochemical control of nematodes, there are still considerable gaps in the knowledge regarding the effectiveness against the major species, and there have been no studies to evaluate possible improved control through synergism i.e. with mixtures of phytochemicals from different nematicidal species. There have also been no studies on the physico-chemical effects of soil on the effectiveness of the phytochemicals e.g. effects of soil pH and organic matter content. The aims of this project are to combine the considerable expertise within the three universities and apply this knowledge to the evaluation of phytochemicals as effective, and safer, control agents for economically important nematodes: UTAD (phytochemical analyses, phytochemistry of glucosinolate-containing species and biological activities of phytochemicals [including control of Globodera with Brassica species]), UE (nematology and data modeling) and FCUL (production, extraction, and analyses of essential oil-producing species). The project is divided into the following major tasks: 1) the production and analyses of plant material, plant extracts for screening for nematicidal activities (plant material selected on the basis of previous research and ease of production of material [plant growth and cost of production]), 2) the development of robust in vitro bioassays for soil-borne and aerial nematodes and evaluation of soil properties on phytochemical effectiveness, 3) dose-response studies for the four nematode species (Globodera, Heterodera, Meloidogyne, and Bursaphelenchus xylophilus) with crude plant material and various fractions from the selected plant species (single extracts and synergism studies), 4) modeling the data for correlating dose-response curves and extrapolation to field conditions, 5) combining all the results for evaluating the effectiveness of the different phytochemicals and development of an effective nematicide. It is expected that at the end of the research species-specific natural nematicides, and possibly a multi-species nematicide, based on phytochemicals from either single plant species or a combination of the species for maximal nematicidal activity, will have been identified.