In the present study, the spread of Rhizoctonia solani-induced disease was limited when cucumber plants were pretreated with Trichoderma atroviride TRS25. The systemic disease suppression was related to TRS25-induced resistance (TISR) induction with simultaneous plant growth promotion. Protection of cucumber was related to enhanced activity of defense enzymes, e.g., guaiacol peroxidase (GPX), syringaldazine peroxidase (SPX), phenylalanine ammonia lyase (PAL), and polyphenol oxidase (PPO) as well as phenolic (PC) concentration increases in the conditions of hydrogen peroxide (H₂O₂) accumulation, resulting in thiobarbituric acid reactive substance (TBARS) decrease. Moreover, the obtained results indicated that TISR might depend on accumulation of salicylic acid derivatives, that is methyl salicylate (MeSA), ethylhexyl salicylate (EHS), salicylic acid glucosylated conjugates (SAGC), and β-cyclocitral as well as volatile organic compounds (VOC) such as Z-3-hexanal, Z-3-hexenol, and E-2-hexenal. The results point to important, not previously documented, roles of these VOC in TISR signaling with up-regulation of PR1 and PR5 gene characteristic of systemic acquired resistance (SAR) and of PR4 gene, marker of induced systemic resistance (ISR). The study established that TRS25 enhanced deposition of callose and lignin in specialized plant cells, which protected vascular system in cucumber shoots and roots as well as assimilation cells and dermal tissues in shoots and leaves. These compounds protected cucumber organs against R. solani influence and made them more flexible and resilient, which contributed to better nutrition and hydration of plants. The growth promotion coupled with systemic mobilization of biochemical and mechanical strengthening might be involved in multilayer protection of cucumber against R. solani activated by TRS25.

This article reports events connected to cell survival and Botrytis cinerea infection development in cell suspension cultures of two tomato cultivars which show different levels of susceptibility to the pathogen: cv. Corindo (more susceptible) and cv. Perkoz (less susceptible). In parallel changes in reactive oxygen (ROS) and nitrogen (RNS) species generation and in S-nitrosoglutathione reductase (GSNOR) activity were studied. In vivo staining methods with acridine orange (AO) and ethidium bromide (EB) as well as fluorescent microscopy were used to assess tomato and B. cinerea cells death. The biochemical studies of ROS and RNS concentrations in plant cell extract were complemented by in vivo ROS and nitric oxide (NO) imaging using nitro blue tetrazolium (NBT), diaminobenzidine (DAB) and diaminofluorescein diacetate (DAF-DA) staining methods, and confocal microscope technique. B. cinerea infection proceeded slower in Perkoz cell cultures. It was evidenced by measuring the pathogen conidia germination and germination tube development in which nuclei revealing cell death dominated. Two different types of tomato cell death were observed: cells with necrotic nuclei dominated in Corindo whereas in Perkoz cells with characteristic of vacuolar death type prevailed. In Perkoz cells, constitutive levels of NO and S-nitrosothiols (SNO) were significantly higher and hydrogen peroxide (H₂O₂) and superoxide anion (O₂ ⁻) concentrations were slightly higher as compared with Corindo cells. Moreover, increases in these molecule concentrations as a result of B. cinerea inoculation were observed in both, Perkoz and Corindo cell cultures. The enzymatic GSNOR activity seems to be an important player in controlling the SNO level in tomato cells. Involvements of the studied compounds in molecular mechanisms of tomato resistance to B. cinerea are discussed in the paper.

In the present study, T. atroviride TRS25 is presented as a biological control agent which significantly limits the development of infection and reduces the disease caused by the pathogenic fungus R. solani in cucumber plants (C. sativus L.). The systemic disease suppression is related to oxidative, signaling and biochemical changes which may trigger cucumber defensive reactions to the pathogen. Induction of systemic defence in cucumber by TRS25 greatly depends on the accumulation of signaling molecules including hydrogen peroxide (H2O2) and nitric oxide (NO) as well as salicylic acid (SA) and its derivatives including methyl salicylate (MeSA) and octyl salicylate (OSA). The study established that NO was accumulated in leaves and shoots of the cucumber plants, especially those pretreated witch Trichoderma and inoculated with R. solani, where the compound was accumulated mainly in the cells localized in the vascular bundles and in dermal tissues. We suggest, for the first time, that in the plants pretreated with TRS25 the accumulation of H2O2 and NO may be related to catalase (CAT) and S-nitrosoglutathione reductase (GSNOR) activity decrease. On the other hand, excessive accumulation of NO and SA may be controlled by forming their inactive forms, S-nitrosothiols (SNO) and salicylic acid glucosylated conjugates (SAGC), respectively. The obtained results suggest that the mentioned molecules may be an important components of the complex signaling network activated by TRS25, which is positively involved in systemic defence responses of cucumber plants against R. solani.

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Interaction of tomato roots with Trichoderma virens TRS106 provided protection against Rhizoctonia solani-induced disease. In tomato, plants inoculated with R. solani disease symptoms were observed on the roots as brown, necrotic lesions. These symptoms were limited on plants treated with TRS106 and inoculated with R. solani. It was shown that TRS106 did not directly inhibit Rhizoctonia growth in in vitro test. The tested Trichoderma isolate stimulated systemic defence responses in tomato plants, by activating defence enzymes including guaiacol peroxidase (GPX), syringaldazine peroxidase (SPX) and phenylalanine ammonia lyase (PAL). Simultaneously, it enhanced accumulation of phenolics and hydrogen peroxide (H₂O₂) accompanied by decrease in lipid peroxidation in the leaves. HPLC analysis indicated remarkable increases in the concentrations of 22 phenolics in the leaves of Trichoderma-treated tomato, both uninoculated and inoculated with R. solani. Some of the phenolics were present in a free form, the others were accumulated in a bound form as glycosylated conjugates belonging to phenylpropanoids, hydroxybenzoic and cinnamic acid derivatives and flavonoids. Several of the detected phenolics: ferulic and salicylic acids, pyrocatechol and hesperetin were strongly toxic to R. solani in plate tests. The systemic mobilisation of phenolic metabolism might be an element of tomato defence response positively involved in biocontrol of R. solani by TRS106. Based on the results, T. virens TRS106 may have potential to develop a new biofungicide for integrated management of R. solani-induced disease.