Pleurotus ostreatus is one of the most widespread mushrooms in the world. It is a valuable and widely cultivated edible mushroom with nematicidal properties. The mycelium of this mushroom produces a toxin that paralyzes nematodes, after which the nematode becomes infected with the filament, resulting in its death. This feature can be put to practical use as a natural nematicidal agent. In this paper, we have described studies on two wild strains of P. ostreatus (PO1, PO2) and the monokaryotic progeny obtained from their fruiting bodies. Monokaryons were crossed with each other within the progeny of one strain (PO1xPO1; PO2xPO2) and of two different strains (PO2xPO1). The growth conditions, morphological and molecular characteristics, toxicity and ability to form hyphal knobs of the maternal strains, monokaryons and those obtained by crossing were studied. The toxicity of mycelium was tested against the model organism Caenorhabditis elegans. The results of the study allowed the selection of five progeny heterokaryotic mycelia with the best parameters useful for in-vitro control of nematodes.

Plant pathogenic nematodes play an important role in crop production and are difficult to control. One of them is Heterodera schachtii—a cyst nematode, pathogenic to sugar beet. Nature suggests a natural way to resolve this problem by using nematode-trapping fungi, one of which is Pleurotus ostreatus. It is one of the most widespread mushrooms in the world. It is a valuable and widely cultivated edible mushroom with nematocidal properties. The mycelium of this mushroom produces toxin droplets that paralyze nematodes, after which the nematodes become infected with the hyphae filament, resulting in their death. This feature can be put to practical use as a natural nematocidal agent. In this paper, we have described studies on the variability of the nematocidal properties in the progeny of three wild strains of P. ostreatus (Po1, Po2, Po4), obtained by crossing dikaryons with monokaryons (Buller phenomenon). The toxicity of mycelium was tested against the model organism Caenorhabditis elegans and against sugar beet pest—H. schachtii. The results of the study allowed the selection of the progeny heterokaryotic mycelia with the best parameters useful for in vitro control of both nematodes. They differed in the activity against C. elegans and H. schachtii, and in the toxic knobs production. The results indicated that the progeny of the Po1 strain presented a good ability to produce hyphal knobs in the presence of C. elegans, and progenies of the Po4 strain presented good quality of growth in preferred temperatures (10–25 °C). Three strains Po1 5dix27, Po2 20dix21, and Po4 2dix1, as well as a maternal strain Po4 controlled H. schachtii by entwining cysts better than other strains. These strains were moderately effective against C. elegans. Strains Po2 15dix17, Po4 1dix18, and Po4 1dix30 may be considered good controlling isolates against both tested organisms. The results of the research also clearly suggest that the killing properties of P. ostreatus mycelia should not be assessed only by their ability to produce toxic hyphal knobs. Their nematocidal properties also depend on other mechanisms developed by mycelia, which is observed as the lethality of nematodes. The results of this research will lead to a natural way to protect plants against nematodes. The research also proved the nematocidal properties of the wild strains to reduce the H. schachtii population in the soil.

Fungi show the excellent way to protect themselves against mycpphagous nematodes. For this purpose, they developed various means of protection, starting form creating traps, toxins production, adhesive spores and mycelia, and finishing on enzymatic predation leading to digestion of nematode body. They are also able to counteract the increase in the number of nematodes by ovi-parasitism and enzymatic digestion of eggs. Nature abounds in numerous examples of fungi with nematicidal activity. They belong to almost all the main fungal taxa and also may be found among fungi-like organisms. The nematicidal activity of fungi opens the gate with many interesting opportunities to use them in biological control of plant-parasitic nematodes as well as animal parasites. So far, only a few of that type fungi were used as the main active ingredient of nematicidal bio- preparations. This includes Paecilomyces lilacinus, Myrothecium verrucaria, Aspergillus niger, Pochonia chlamydosporia, Purpureocillium lilacinus, Trichoderma harzianum and T. viride.

The objective of these studies was to identify differences and similarities within the progeny of Rhizoctonia solani AG5, which arose from basidiospores produced by the maternal strain ID23. The following characteristics were analyzed: appearance of the mycelium (color, structure, zonation, and presence of sclerotia), growth rate (at 10°C, 20°C, and 30°C), fungicide sensitivity, and hyphal structure. The mycelial color of R. solani AG5 ranged from white/cream to light and dark brown. The structure of the mycelium may be compacted or flattened with visible zoning or fluffy with dark brown sclerotia on the colony surface. Homokaryons and heterokaryons derived from homokaryons were analyzed by constructing a phylogenetic tree using morphological data. Single basidiospore-grown isolates formed a separate subclade, the majority of which were grouped with a maternal isolate; however, heterokaryons derived from them created a separate subclade. In addition, isolates grown in basidiospores germinated at low temperatures created their own group, but with some exceptions. This shows a divergence in the morphological parameters of the subsequent generations and within generations. The optimal temperature for growth was found to be between 20°C and 30°C. The exceptions were strains obtained from basidiospores that germinated at refrigerated temperatures. For these samples, 10°C was found to be the optimal growth temperature. The hyphae of homokaryons were characterized by the presence of branching at an almost right angle and the presence of a septum at the site of constriction of the branch itself. The mean diameter of hyphae ranged 2.93–15.60 μm, depending on the age of hyphae. The fungicidal compounds at a concentration of 10 ppm had no significant effect on the activity of the tested strains, whereas a tenfold increase in the dose reduced the growth ability of the tested isolates. The activity of fungicides containing azoxystrobin, thiuram, or thiophanate-methyl on R. solani resulted in a reduction in the mycelial growth rate only in the case of azoxystrobin and thiuram, and in some cases, it was completely inhibited (thiophanate-methyl).

Food resources are essential for the survival and growth of the population. Soil phytopathogenic nematodes cause great damage to agricultural crops, endangering food supplies and resources in general. Different methods have been used to control them. However, this issue still requires a more effective solution. Caenorhabditis elegans (CGC strain wild-type N2) was applied as a model with an Escherichia coli OP50 feeding substrate for nematodes. Our approach was based on the thermodynamically substantiated creation of growth conditions that are unfavorable for nematodes to suppress them irreversibly. The thermodynamic calculations showed that obligate anaerobic conditions, namely the absence of oxygen and a low redox potential (−100 mV and below), were potentially unacceptable for nematodes. Anaerobic conditions were created using both abiogenic (physicochemical) and biological methods. Abiogenic anaerobic conditions were achieved by preventing oxygen access and adding low-potential sodium sulfide (Eh = −250...−200 mV) to the cultivation medium. By applying biological methods, Pleurotus ostreatus Po4 and E. coli O₂ was completely removed and the redox potential was decreased from +100…+200 mV to −100...−200 mV (in particular, due to the synthesis of H₂S). Even the short-term exposure (1–2 days) of nematodes under anaerobic conditions led to their suppression and death. Thus, the short-term creation of anaerobic conditions in the soil may be an effective method to control, e.g., phytopathogenic aerobic nematodes. This research contributes to the development of foundations to preserve agricultural plants and increase crop yield as well as the development of an approach for the environmentally friendly control of phytopathogens.