Significance of volatile compounds released by roots of cultivated plants for indirect defence against soil pests

Plants in nature have developed various defence mechanisms against attacks by harmful organisms, these mechanisms are either indirect or direct. When attacked by harmful organisms, many plant species release volatile compounds (VOCs) which attract natural enemies of herbivores. VOCs have an important role in a multitrophic system, which consists of a plant, a herbivore and its natural enemy. Their function is a chemical signal which directly influence both herbivore and its natural enemy. Certain compounds are produced both by damaged and undamaged plants. VOCs released by plants affect organisms in rhizosphere at different trophic levels either as attractants or as repellents. Studies of VOCs released by roots necessitate the use of modern gas chromatography with mass spectrometric detection (GC-MS), since this technique enables detection and identification of compounds which are present in small quantities and concentrations. A quantitative and qualitative changes occur in certain metabolites of aboveground parts of the plants when roots are damaged by soil dwelling herbivore. Most of the plant induced responses to the biotic stress are systemic. Induced systemic resistance in plants against many pests has been correlated also with the synthesis and accumulation of antioxidants and antioxidant enzymes. Biological control is a way of controlling harmful organisms in agriculture and forestry by using living natural enemies (beneficial organisms) or pesticides of biological origins. It is directed toward protection, stimulation and targeted introduction of beneficial organisms outdoors or indoors. Biological preparations are ecologically more suitable, their effects are more specific, their formulation and application should be paid particular attention, and optimal times of application should be strictly observed. We are proposing the research that will focus on studying the chemical communication of indigenous and commercial strains of entomopathogenic nematodes (EPNs) (Steinernema feltiae; S. carpocapsae; S. kraussei; Heterorhabditis bacteriophora) with damaged and undamaged roots of the red pepper (Capsicum annum), lettuce (Lactuca sativa) and horseradish (Armoracia rusticana). The roots will be exposed for damage to soil pests, namely wireworms (Agriotes spp., Elateridae). Goals of the study are (1) to enrich the existing knowledge about multitrophic communications in rhizosphere; (2) to detect the principal communicators with EPNs– a constitutive or herbivore induced plant metabolites; (3) to evaluate the potential of biologically active VOCs as agents in plant protection against soil pests; (4) to develop optimised procedures for sampling and analysis of semiochemicals on the selected organisms. The hypothesis is that a plant produces semiochemicals which trigger activity of EPNs as attractants. If confirmed, the results and gained knowledge can be exploited to develop pheromone capsules based on the main active compounds which would attract EPNs to the roots of plants in larger numbers and would thus ensure their better protecion. Knowledge about the communication between plants, herbivores, and their natural enemies is crucial for more efficient implementation and optimisation of biological control in food production systems.