An approach to manage seed-transmitted Fusarium crown-foot-root rot (FCR, Fusarium spp.) and common root rot (CRR, Bipolaris sorokiniana) on wheat, avoiding environmental risks of chemicals, is seed treatments with microbial metabolites. F. sambucinum strain FS-94 that induces resistance to tomato wilt was shown by this study to be a source of non-fungitoxic wheat-protecting metabolites, which were contained in a mycelium extract purified by gel-chromatography and ultrafiltration. Plant-protecting effect of the purified mycelial extract (PME) was demonstrated in vegetation experiments using a rolled-towel assay and by small-plot field trials. To elucidate mechanisms putatively underlying PME protective activity, tests with cultured Triticum aestivum and T. kiharae cells, particularly the extracellular alkalinization assay, as well as gene expression analysis in germinated wheat seeds were used. Pre-inoculation treatments of seeds with PME significantly decreased the incidence (from 30 to 40%) and severity (from 37 to 50%) of root rots on seedlings without any inhibition of the seed germination and potentiation of deoxynivalenol (DON), DON monoacetylated derivatives and zearalenon production in FCR agents. In vegetation experiments, reductions in the DON production were observed with doses of 0.5 and 1 mg/mL of PME. Pre-sowing PME application on seeds of two spring wheat cultivars naturally infected with FCR and CRR provided the mitigation of both diseases under field conditions during four growing seasons (2013–2016). PME-induced ion exchange response in cultured wheat cells, their increased survivability, and up-regulated expression of some defensins’ genes in PME-exposed seedlings allow the suggestion of the plant-mediated character of disease-controlling effect observed in field.

The wheat rhizosphere-inhabiting nonpathogenic Fusarium sambucinum isolate FS-94 protected tomato from Fusarium wilt (F. oxysporum f. sp. lycopersici) in laboratory experiments. Seed soaking or immersion of seedling roots in a FS-94 spore suspension prior to inoculation with the pathogen delayed the appearance of wilt symptoms and significantly reduced disease severity in plants of a susceptible tomato cultivar. Quantification of fungal ergosterol in infected tomato showed that protection against wilt agent was related to limitation of the pathogen growth in plants exposed to FS-94. Incubation of tomato seedlings in a FS-94 spore suspension for 48 or 72 h led to plant protection and increased the salicylic acid (SA) concentration in their roots, suggesting that this isolate was involved in a plant-mediated mode of action and induced resistance. Soaking tomato seeds in the spore suspension did not induce SA accumulation in seedling roots, but nevertheless resulted in a significant reduction in wilt severity when the seedlings were challenged with the pathogen. In response to pathogen attack, the SA content in susceptible seedlings grown from FS-94-treated seeds started to increase within 1 day and remained elevated for 72 h. This suggests that F. sambucinum isolate FS-94 primed a SA-dependent signaling system in tomato.

This paper reports the first results on obtaining an enzyme preparation that might be promising for the simultaneous decontamination of plant feeds contaminated with a polyketide fusariotoxin, zearalenone (ZEN), and enhancing the availability of their nutritional components. A novel ZEN-specific lactonohydrolase (ZHD) was expressed in a Penicillium canescens strain PCA-10 that was developed previously as a producer of different hydrolytic enzymes for feed biorefinery. The recombinant ZHD secreted by transformed fungal clones into culture liquid was shown to remove the toxin from model solutions, and was able to decontaminate wheat grain artificially infected with a zearalenone-producing Fusarium culmorum. The dynamics of ZEN degradation depending on the temperature and pH of the incubation media was investigated, and the optimal values of these parameters (pH 8.5, 30 °C) for the ZHD-containing enzyme preparation (PR-ZHD) were determined. Under these conditions, the 3 h co-incubation of ZEN and PR-ZHD resulted in a complete removal of the toxin from the model solutions, while the PR-ZHD addition (8 mg/g of dried grain) to flour samples prepared from the infected ZEN-polluted grain (about 16 µg/g) completely decontaminated the samples after an overnight exposure.

Forage grain contamination with aflatoxin B1 (AFB1) is a global problem, so its detoxification with the aim of providing feed safety and cost-efficiency is still a relevant issue. AFB1 degradation by microbial enzymes is considered to be a promising detoxification approach. In this study, we modified an previously developed Pichia pastoris GS115 expression system using a chimeric signal peptide to obtain a new recombinant producer of extracellular AFB1 oxidase (AFO) from Armillaria tabescens (the yield of 0.3 g/L), purified AFO, and selected optimal conditions for AFO-induced AFB1 removal from model solutions. After a 72 h exposure of the AFB1 solution to AFO at pH 6.0 and 30 °C, 80% of the AFB1 was degraded. Treatments with AFO also significantly reduced the AFB1 content in wheat and corn grain inoculated with Aspergillus flavus. In grain samples contaminated with several dozen micrograms of AFB1 per kg, a 48 h exposure to AFO resulted in at least double the reduction in grain contamination compared to the control, while the same treatment of more significantly (~mg/kg) AFB1-polluted samples reduced their contamination by ~40%. These findings prove the potential of the tested AFO for cereal grain decontamination and suggest that additional studies to stabilize AFO and improve its AFB1-degrading efficacy are required.

Zearalenone (ZEN) and deoxynivalenol (DON) are mycotoxins produced by various species of Fusarium fungi. They contaminate agricultural products and negatively influence human and animal health, thus representing a serious problem of the agricultural industry. Earlier we showed that compactin, a secondary metabolite of Penicillium citrinum, is able to completely suppress the aflatoxin B1 biosynthesis by Aspergillus flavus. Using the F. culmorum strain FC-19 able to produce DON and ZEN, we demonstrated that compactin also significantly suppressed both DON (99.3%) and ZEN (100%) biosynthesis. The possible mechanisms of this suppression were elucidated by qPCR-based analysis of expression levels of 48 biosynthetic and regulatory genes. Expression of eight of 13 TRI genes, including TRI4, TRI5, and TRI101, was completely suppressed. A significant down-regulation was revealed for the TRI10, TRI9, and TRI14 genes. TRI15 was the only up-regulated gene from the TRI cluster. In the case of the ZEN cluster, almost complete suppression was observed for PKS4, PKS13, and ZEB1 genes, and the balance between two ZEB2 isoforms was altered. Among regulatory genes, an increased expression of GPA1 and GPA2 genes encoding α- and β-subunits of a G-protein was shown, whereas eight genes were down-regulated. The obtained results suggest that the main pathway for a compactin-related inhibition of the DON and ZEN biosynthesis affects the transcription of genes involved in the G-protein-cAMP-PKA signaling pathway. The revealed gene expression data may provide a better understanding of genetic mechanisms underlying mycotoxin production and its regulation.