# Nematoidal Properties of Wild Strains of _Pleurotus ostreatus_
## 1 Introduction  
Nematodes play an important role in the environment, and they are also significant for agriculture. Among them, many species are severe plant pathogens, which reduce crop yield. One of them is _Heterodera schachtii_, a cyst nematode pathogenic to sugar beets. This nematode significantly reduces root and sugar yields and the sugar content in roots. _H. _schachtii_ has a very wide host range (over 200 plant species) and a very long lifespan in the soil (up to twenty years) [1]. Despite the threat this pathogen presents in sugar beet crops, it is still difficult to control. This pest attacks beet plants throughout the entire growing season, producing two and sometimes three generations per year in a moderate climate. The dynamics of its development are significantly influenced by soil temperature and humidity. If conditions are favorable for early hatching of larvae, the roots of young beet plants are damaged. This reduces field stands, increasing the sensitivity of plants to other soil pathogens and drought, and also promotes subsequent root damage, which results in crop losses. The population of the beetroot cyst nematode _H. schachtii_ increases very quickly in fields where beets and cruciferous plants are cultivated in crop rotation. The basic rule in the fight against this pest is to prevent the introduction of the cyst nematode into the field, to grow plants tolerant to the cyst nematode (particularly in the case of sugar beets), and to introduce a minimum three-year break in the cultivation of sugar beets and other host plants. Another supportive method is the cultivation of pre-crops, called \"anti-nematode catch crops\", such as white mustard and oil radish. Nematode populations can also be reduced by growing other plant species (e.g., rye or corn) that activate cyst nematodes and prevent them from developing a full life cycle. Taking into account the limited ways of controlling the sugar beet cyst nematode _H. schachtii_ and other nematodes that are harmful to plants, which are limited only to biological methods, it is worth testing other antagonistic factors for pathogenic nematodes. The scientific literature provides numerous methods of combating various nematodes using fungi and bacteria [2; 3]. One such example is the nematocidal activity of the oyster mushroom (_Pleurotus ostreatus_), which, in the presence of nematodes, produces small structures, hyphal knobs, containing toxins directed against nematodes. This ability protects hyphae against mycophagy and provides an additional source of nitrogen for the developing vegetative mycelium [3; 4; 5]. Other species of fungi produce traps in the form of loops of hyphae and sticky projections [6]. Toxins produced by _P. ostreatus_ vegetative mycelium in tiny protrusions containing droplets of toxin (hyphal knobs, toxocysts) immobilize nematodes in as little as 30 s [3; 4; 7]. The toxin was reported as a compound with a strong effect because within 1 h, at a concentration of 300 ppm, it can immobilize 95% of nematodes. This toxin, called ovastatin, was identified as trans-2-decenediotic acid [8]. Ostreatin is secreted by vegetative hyphae and does not occur in the fruiting bodies of _Pleurotus_ sp. Its main function is to protect the mycelium against mites, tardigrades, and springtails [9]. The toxin's mode of action is based on affecting the permeability of the cell membrane, which disrupts the function of nerve and muscle cells. Trans-2-decenedioic acid is a simple natural compound, which is important for its subsequent biodegradation [8]. Also, other substances were considered as active molecules produced by mycelium, including the ribotoxin-like protein that is also named ovastatin [9; 10]. Despite the discovery of this phenomenon quite a long time ago, so far not many studies have been carried out on the variability of the toxic properties within _P. ostreatus_ populations and its offspring. However, data from the research of [PERSON] and coworkers [10], published last time, showed another compound responsible for the toxic activity of _P.