Potential of biological approaches for soil pest control in greenhouse vegetable crops

The production of vegetables in greenhouses results in continuous and rhythmical supply of the market with fresh produce. It is characterized by innovation and dynamic development. Besides positive sides, greenhouse vegetable production has same negatives. Inability to apply balanced crop rotations and closed space lead to worsening of the nutrient regime and rapid multiplication of pests. Good Agricultural Practices (GAP), including the good plant protection practice (GPPP) is necessary to be kept in order to prevent these negatives. Significant disadvantages of chemical control, including the threat to human health and the environment, transform the biological control in one of the most promising alternatives. Recently a progress in the production of a number of biological agents is observed and some of these products are already on the market. Biological control agents have a great influence on the regulation of the population of root-knot nematodes and pathogens and they are applied in combination with other strategies for management. The most common are: Bacillus spp. Species from Bacillus genus are most commonly used as bio-pesticides to control disease and plant nematodes. They could control the fungal pathogens through competition, direct antibiosis and induced resistance. The most popular biological control agents are B. subtilis, B. thuringiensi, B. amyloliquefasciens, B. firmus and B. pumilus. Pseudomonas spp. Pseudomonads possess many qualities that make them for biocontrol and growth-promoting agents. They produce a wide range of bioactive metabolites - antibiotics siderophores, volatile and growth-promoting substances. They enter into completion aggressively with other microorganisms and they could adapt quickly to the environment. Pasteuria spp. The distribution of Pasteuria spp. in the body of the nematode induces degeneration of the reproductive tissues, and significantly reduces the fertility. Because of the high efficiency and specificity to the host, P. penetrans is a potentially perfect agent for biological control against economically important nematodes of the genus Meloidogyne. Paecilomyces lilacinus. This species parasitizes and subsequently kills eggs, larvae and adults of various plant-parasitic nematodes - Meloidogyne spp., Radopholus similis, Heterodera spp., Pratylenchus spp., Globodera spp. Trichoderma spp. Strains belonging to the Trichoderma genus have been identified as biological control agents against plant diseases and nematodes. Some of these strains are developed and registered as biofungicides. The species T. harzianum, T. viride, T. atroviride, T. asperellum, T. gamsii, T. polysporum are very effective as biological control agents. Some strains demonstrate direct hyper-parasitic activity against the pathogen, while in other strains the induction of resistance or competition with pathogens for space and nutrients predominate. The Trichoderma strains produce a great variety of lytic enzymes, which play an important role in biocontrol. They showed antifungal activity towards a broad spectrum of fungal pathogens (Rhizoctonia, Fusarium, Alternaria, Ustilago, Venturia, Colletotrichum, Pythium and Phytophthora). One of the main restrictive factors for the widespread use of microbial biological control agents is their price compared to the chemical fumigants. The practical application of bio-agents also requires special knowledge and a set of specific conditions guaranteeing high efficiency in their application. Microbial plant protection products are a subject of researches in the „Maritsa” Vegetable Crops Research Institute - Plovdiv. Microorganisms for bio-control of phytopathogens and nematodes - Trichoderma viride strain T6; Bacillus amyloliquefaciens strain A1; Bacillus thuringiensis strain Bt1; Bacillus amyloliquefaciens strain 2/7 A are studied. The results show that the use of micro-bioagents could lead to an effective control of the soil pathogens and root-knot nematodes as well as to production free of pesticide. This is an alternative to chemical nematocides, which in recent years have given way to the ecological methods. Recently the interest both in recycling organic waste composting technology, including a vermicomposting and more widespread use of such products in practice continuously increases. The application of compost in vegetable cultivation has a positive effect on growth, yield and plant health status. This is due to the high microbiological activity, which depletes the available nutrients for the survival and reproduction of the pathogen. Development of varieties with complex resistance to economically important diseases and pests is of great importance for limiting of the pesticide use and for obtaining of healthier vegetable production as part of the diet of people. This is an ecological alternative method to control soil pests. Grafting is an appropriate method that could also be integrated in the system for soil pest control. However the grafted culture could be tolerant to a range of pathogens and nematodes, but sensitive to other. The same effect could be observed in any kind of organic products improving the soil, including compost, green manure and organic mulch. The organic enhancers may both increase the tolerance of the host-plant and reduce the population of nematodes. It was established that some field crops and cover crops (cereals and legumes) are non-host crops for nematodes. Many Brassica species manifest nematocidic activity against various plant-parasitic nematodes, including Meloidogyne incognita, M. javanica, Heterodera schachtii and Pratylenchus neglectus. Searching and establishment of alternative methods to control soil pests by optimally combined use of bioresources will give a possibility for production of quality and healthy greenhouse vegetable produce.BG; bg; EFSAfocalpoint@mzh.government.b