1. Introduction
White button mushroom
Agaricus bisporus (J.E. Lange) Imbach has been artificially cultivated for over 450 years, and has become one of the major crop [
1,
2,
3]. The main problem of its farming is the yield instability. Even when keeping every approved technological rule, the grower often cannot predict with complete certainty the optimal yield. One this phenomenon reasons is the crop diseases which harmfulness in intensive cultivating technologies is yet high [
4,
5]. In this regard, the study of organisms responsible for white button mushroom yield losses isn’t losing relevance for the scientifically motivated measures development to their control [
6]. The science and practice of mushroom farming has developed certain preventive measures to reduce the harm caused to the mushroom culture. The main of them, used both in our country and abroad: compliance with the compost and casing soil preparative technologies, hygienic requirements keeping when performing work in mushroom houses; disease-resistant
A. bisporus strains use; regular pre-sawing and inter-cycling preventive measures use in cultivation facilities, nutrients and hormones introducing; compliance with microclimate technological parameters at all stages of culture development; chemicals limited set using to protect mushrooms [
7,
8]. Nevertheless, the full measures complex implementing often does not lead to the desired results, in the mushroom production process the optimal and stable yield cannot be ensured precisely because of the crop diseases caused mainly by micromycetes. The main representative of the white button mushroom mycopathogenic complex is the wet bubble causative agent
Mycogone perniciosa Magn. [
9,
10]. The disease manifests in the basidiomata deformation with the subsequent bacteria development on them as a secondary infection, causing intense fruit body rotting [
4,
9,
10]. The disease occurs in the industrial mushroom-growing farms almost everywhere when conditions are favorable for its emergence and development: temperature 16–20° C, humidity over 90 % [
5,
7].
M. perniciosa has a high viability. In culture, the micromycete retained its vital functions for 18 months; in nature, its spores retain viability for up to 3 years; when thermally treated, they withstand a temperature of 60° C for more than 2 h; the mycelium dies within 30 min at this temperature.
M. perniciosa and
A. bisporus develop in almost the same temperature and pH ranges, but they are somewhat wider for the mycoparasite (20–28° C, pH=5–7) than for the host (22–24° C, pH=5.5–5.6) [
11].
Most often, the disease occurs at the end of the growing cycle, when the main crop is weakened and depleted, when mushroom beds are no longer adequately maintained, ventilation deteriorates, and the number of pathogens insect vectors increases [
4]. Wet bubble is the most harmful disease of cultivated mushrooms. Its appearance often leads to the entire crop loss in the cultivation chamber [
4]. In its metabolism,
M. perniciosa acidifies the habitat, which helps it develop insensibility to chemicals, particularly benomyl [
12,
13].
M. perniciosa is an optional biotroph [
14]. Its spores germinate on the
A. bisporus mycelium in the casing, and from there the mycopathogen’s hyphae penetrate into the fruit body anlage and thus into basidioma base. Mycopathogen spores can also germinate on already formed fruit bodies, but in this case, they do not cause serious damage to the host cells. On dead
A. bisporus mycelium
M. perniciosa spores germinate well and the micromycete actively develops; thus, the primary infection occurs through mycelial strands, especially through dead ones left after basidiomata harvesting. From there, the parasite mycelium passes to the living mycelial pulls and then to the generative formations–that is sclerodermoid infestation form. The common one (infestating formed basidiomata) does not cause fruit bodies deformation, they stayed covered with a white
M. perniciosa mycelium. Such infestation form is very rare. It is important to note the lack of correlation between the basidiomata resistance and their mycelium antagonistic activity to
M. perniciosa. The infection persists in the casing as the chlamydospores [
15,
16]. Mycopathogen conidia and chlamydospores usually do not persist in compost because temperatures reach 70–80° C during its processing, but the source of infection can also be compost if phytosanitary rules are violated during its preparation and transportation [
17].
The microbiological control of white button mushroom diseases has not yet found wide application in its industrial cultivation, despite the natural protective mechanisms use manifesting in regulating pest populations number by their antagonists has recently become a priority in the agricultural crops’ protection. Agroecosystems phytosanitary optimizing involves the use of microorganisms with high ecological plasticity and various biologically active substances (BAS) complexes as polyfunctional biologics producer strains with complex biological activity.
Bacillus bacteria, unpretentious with respect to growth conditions, high-tech, capable of producing many BAS and regulating the pathogen populations density when introduced into the agrobiocenosis for a long time, meet such requirements [
18,
19,
20].
Bacillus subtilis strains B-10, M-22 highly effective against a wide range of various cultivated plants phytopathogens have been deposited and passported at the FSBSI VIZR Microbiocontrol laboratory [
20]. The research-industrial technologies for polyfunctional biologics preparing on their basis were developed and biologics included in the State catalog of pesticides and agrochemicals permitted for use in Russian Federation territory (2023) [
21]. These biologics have high biological efficacy (60–90 %) against pathogens of the most harmful diseases, their formulation include live cells and metabolome that determine the antagonistic activity, as well as polypeptide antibiotics of original structure [
22]. From the above, the research goal was to characterize the effect of
B. subtilis B-10 and M-22 producer strains on
M. perniciosa and evaluate the possibility of wet bubble control using antagonist microbes, the basis of polyfunctional biologics. To achieve this goal, the following tasks were solved: to compare the effect of
B. subtilis B-10 and M-22 producer strains on 1-day- and 7-day-old
M. perniciosa colonies when applied by spraying and into the agar wells (methods simulating basidioma and casing soil treatments); to identify the most active antagonist to
M. perniciosa; to evaluate the ability of the studied producer strains to suppress the wet bubble disease development.
Author Contributions
Conceptualization, J.T. and I.N.; methodology, J.T. and I.N.; software, J.T.; validation, J.T. and I.N.; formal analysis, I.N.; investigation, J.T.; resources, I.N.; data curation, J.T.; writing—original draft preparation, J.T.; writing—review and editing, J.T. and I.N.; visualization, J.T.; supervision, I.N.; project administration, J.T. and I.N.; funding acquisition, I.N. All authors have read and agreed to the published version of the manuscript.