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Extracellular metabolites of Gliocladium roseum GRZ7 are able to destroy aflatoxin B1 and zearalenone (by 61.9 and 68%, respectively). The determined optimum pH and temperature confirm the enzymatic nature of these metabolites.

6-Demethylmevinoliin, a secondary metabolite of Penicillum citrinum, is able to efficiently inhibit the biosynthesis of two polypeptide mycotoxins, aflatoxin B1 and zearalenone, by 92 and 78% of the control, respectively.

Chitosan hydrolyzate containing low-molecular-weight chitosan (≤24 kDa) and its oligomers (≤1.2 kDa) has been obtained via chemical depolimerization of high-molecular-weight chitosan by nitric acid. The fractions of the obtained chitosan hydrolyzate have been characterized by high performance gel permeation chromatography and proton magnetic resonance. The test performed on detached leaves of wheat has shown that the hydrolyzate completely inhibits the development of Stagonospora nodorum, a casual agent of the septoria leaf blotch, at a concentration of 200 μg/mL. A similar test with detached tobacco leaves has shown that the hydrolyzate at a concentration of 100 μg/mL also inhibits the development of Alternaria longipes, which causes brown spot of tobacco, by 75%.

The paper reports the first results of vegetation experiments confirming the earlier observed in vitro sensitizing activity of extracellular elicitors of F. sambucinum FS-94 toward P. nodorum. The data of a small-plot field experiment showing a possibility of using FS-94 culture liquid containing these resistance-eliciting metabolites to reduce effective dosages of Folicure BT, EC 25% (a. i. tebuconazole and triadimefon, triazole derivatives) are also presented.

Commercial fungicides provide an efficient control of fungal diseases of crops. At the same time, plant pathogenic fungi can develop resistance to fungicides that results in epiphytoties and significant yield losses. The most common response of potato growers is more extensive use of fungicides associated with environmental pollution and a range of various health risks. Therefore, the search for approach preventing the development of pest resistance to fungicides is of great practical interest. A potentially new strategy to overcome or minimize this problem is an enhancement of pathogen sensitivity to fungicides using various chemical compounds. In this study, we examined several putative sensitizers chosen among structural analogues of some natural amino acids known for their inhibiting effect on the polyketide biosynthetic pathway, since polyketide mycotoxins play an important role in a pathogenicity of fungi. A possible synergism between the action of these compounds and a commercial fungicide Folicur on the growth of Phoma glomerata and Fusarium culmorum colonies was evaluated using the Limpel’s criterion. For all four compounds tested, a significant chemosensitizing effect was revealed for both non-fungicidal and sub-fungicidal concentrations that confirmed the initial hypothesis. The further screening of other amino acid analogues for their chemosensitizing activity is planned, as well as the study of the mechanism of their sensitizing action. Revealing of a compound providing significant chemosensitizing effect and characterized by a relatively low cost of synthesis would provide a low-cost solution for reduction of fungicidal treatments, while still providing sufficient protection even against fungicide-resistant strains of plant pathogens.Commercial fungicides provide an efficient control of fungal diseases of crops. At the same time, plant pathogenic fungi can develop resistance to fungicides that results in epiphytoties and significant yield losses. The most common response of potato growers is more extensive use of fungicides associated with environmental pollution and a range of various health risks. Therefore, the search for approach preventing the development of pest resistance to fungicides is of great practical interest. A potentially new strategy to overcome or minimize this problem is an enhancement of pathogen sensitivity to fungicides using various chemical compounds. In this study, we examined several putative sensitizers chosen among structural analogues of some natural amino acids known for their inhibiting effect on the polyketide biosynthetic pathway, since polyketide mycotoxins play an important role in a pathogenicity of fungi. A possible synergism between the action of these compounds and a commercial fungicide Folicur ...

Use of natural compounds against phytopathogenic microorganisms instead of chemicals is regarded as the safer approach to protect environment, consumers and the staff. Previously in the laboratory tests, the Pravastatin, an inhibitor of sterol biosynthesis, was shown to prevent development of helminthosporium root rot, caused by Bipolaris sorokiniana, in spring barley seedlings. Further to this, we studied the protective effect of Pravastatin against B. sorokiniana in test field (Moscow Province). Before sowing, the spring barley (variety Zazerskii 85) seeds, naturally infected with B. sorokiniana, were treated with Pravastatin (0.05, 0.075 e 0.1 % for 24 hours). The pre-sowing examination of untreated naturally infected seeds showed the plant damage by helminthospor ium root rot at 8.9 % and the disease severity at 36.8 %. Small-plot field trials showed that treatments of spring barley seeds with soaking in 0.075 or 0.1 % Pravastatin solutions for 24 hours before their sowing decreased the number of plans damaged by B. sorokiniana, as well as reduced the disease severity. The maximal protective effect was produced by Pravastatin at the concentration of 0.1 %. It Ðen. 3. Aeeia iaacaiiie e iiacaiiie ÷anoe (A) e eonoenoinou (A) o ðanoaiee y÷iaiy (Hordeum vulgare L.) niðoa Cacaðneee 85 â eiioa oacu eouaiey (oaca 29) iinea iðaaiinaâiie iaðaaioee naiyi ðanoâiðii iðaâanoaoeia â ðaciuo eiioaioðaoeyo: a — noaaee; a — eiðie (Iineiâneay iae., 2009 aia).

Phytopathogenic fungi exhibit high resistance to extremal environmental conditions, which is largely determined by protective properties of high-molecularweight pigments of different composition contained in them. Melanin of cell walls of the pathogen Magnaporthe grisea that causes blast disease of rise is classified in the widespread type of pigments; it represents a colored polymer of 1,8-dihydroxynaphthalene, the biosynthesis of which depends on acetyl-CoA (the pentaketide pathway) [1]. Analysis of the strains of this fungus defective in pigmentation, which were obtained by induced mutagenesis, showed that blockade of the biosynthesis of melanin attenuates the ability of the fungus to penetrate into leaf tissues and prevents excrescence of the mycelium in the plant, thereby suppressing its pathogenicity [2]. One of the most effective preparations that are used for fighting against blast disease of rice, tricyclazole 1 (Scheme 1), is classified with a small group of fungicides of similar structure, the effect of which is related to selective blockade of the synthesis of the pigment [1]. Another type of inhibitors, which has been represented so far only by the organophosphorous analogue of alanine 2.1 , suppresses the biosynthesis of not only melanin but also other metabolites of the polyketide pathway (including phytotoxins) and exhibits fungitoxicity [3]. In contrast to tricyclazole, which is effective per se , analogue 2.1 is the precursor of the active compound, pyruvate analogue 3.1 , which suppresses the synthesis of acetyl-CoA and melanin (Scheme 2) [4]. A similar mechanism was suggested for the blockade with analogue 2.1 of formation of plant polyketide pigment [5].

Mycotoxins—metabolites of microscopic mold fungi widely spread in nature—are the most hazard� ous pollutants of agricultural raw materials and food� stuff. They are highly toxic and cause severe intoxica� tions in humans and animals; some of them are car� cinogens. The stability of mycotoxins determines the necessity of stringent control of their content in agri� cultural and food products (maximum allowable con� centrations of different mycotoxins are on the order of 0.1–20 mg/kg). The economic damage caused by mycotoxins reaches several billions of dollars every year. It is known that various natural and synthetic com� pounds (ginseng saponins, citrus essential oil, sulfa� mides, organic acids, mercaptoethanol, etc.) can decrease or increase mycotoxin production; however, the causes underlying their activity remain obscure [1]. It was shown that fungicidal activity of some nat� ural phenolic compounds may combine with the abil� ity to suppress toxigenesis [2]. The known method of detoxication of fodders and foodstuff by treatment with ammonia at elevated pressure and temperature has obvious limitations [3]. Thus, the possibility to selectively affect mycotoxin production remains a topical problem. One of its pos� →→ → → →→

Ulocladols A and B — new exometabolites having a mixed sesquiterpenoid-polyketide nature that are structurally close to the host-specific toxins ofAlternaria citri — have been isolated from the deuteromyceteUlocladium chartarum. Both substances inhibit the growth of cotton seeds.

Publisher Summary The chapter discusses the molecular basis of plant immunization. There are several major areas of practical use of plant vaccinations such as the method of protection against viral diseases, prevention of tree infection by root rot causal agents, treatment of the chestnuts infected by the fungus Criphonrectria parasitica and treatment of seeds with rhizospheric bacteria. The principal ideas of studying immunization are based on the experimental data showing that the treatment of plants with attenuated strains of phytopathogenic microorganisms can induce resistance to more pathogenic strains. The section on immunization in plants explains how the chemical protection of plants has been traditionally based on the use of pesticides toxic for pathogenic organisms and how the use of fungicides has undergone three stages in its history. The first- and second-generation fungicides are nonspecific; they possess a broad range of effects on various fungi and do not damage plants. The third-generation fungicides are systemic organic products specific for particular groups of fungi and not toxic for plants. The chapter also describes the agents affecting parasite pathogenicity and the agents influencing plant resistance. Some of the ways of enhanced plant resistance against disease induced by chemical treatment are the building of a protecting film on the leaf surface; enhancement of cell wall resistance against pectolytic enzyme attack; and activation of phenol metabolism, oxidative enzymes, and phytoalexins.

Publisher Summary The chapter describes approaches to obtain plants resistant against disease by means of genetic engineering by plant-pathogen interaction models. Genetic engineering is based on the technology enabling construction of genetic structures in the form of the so-called recombinant (hybrid) molecules (DNA or RNA) in laboratory conditions. The advantages of gene engineering technologies compared with traditional hybridization are (1) hybridization impoverishes the whole genomes of the two parents, and (2) hybridization enables transgenosis only from closely related plants that have no reproduction barriers. Methods of transgenic plant creation include the use of pTi plasmids, use of intermediate vectors, use of binary vectors, pRi plasmids, method of biological ballistics, electroporation, transformation of plant protoplasts, microinjections, and marker genes for transformant selection. The chapter explains transformant regeneration and the development of transgenic plants resistant to viral disease. Some of them are the resistance provided by the expression of the viral coat protein in a plant gene, such as cross-protection of plants against viral infection and transgenosis of viral protein; resistance of transgenic plants induced by expression of transport proteins; and resistance of transgenic plants induced by expression of antiviral antibodies. The chapter also discusses the development of transgenic plants resistant to fungal and bacterial diseases by way of genetic engineering. It also discusses the development of nonplant antibacterial proteins. Mechanisms responsible for susceptibility or resistance in plant–bacterium relationships include general resistance and specific resistance. Some of the topics that are discussed under the sectionon enhancement of natural plant defenses are enhanced production of elicitors, expression of cloned resistance genes, enhanced production of reactive oxygen species, and so on. This chapter also explains the possible limitations of the commercial use of bioengineering methods in the creation of plants resistant to bacterial diseases.

Publisher Summary The nonspecific resistance factors in the horizontal pathosystem are divided into axeny and true resistance. Axeny is the resistance that occurs before a pathogen–plant cell contact, and true resistance is manifested after the pathogen contact with the cellular protoplast. The chapter explains how anatomical–morphological resistance factors are affected by plant habitus, downy leaves, structure and arrangement of stomata, and anatomic features of internal plant tissues. It also explains the regulation of ontogenesis and damage reparation in pathogens. Many plant parasites can penetrate into tissues only through wounds, and the rate of suberization of wound surfaces correlates with plant resistance. It also explains the nutrient value of infected organs and tissues. The chemical factors available to the plants for their own defense against diseases are diverse in chemical composition, conditions of production, and mechanisms of toxicity. This chapter discusses the chemical classification of phytoanticipins, which includes phenols, terpenoids, proteins, and amino acids. Plants possess not only chemically diverse defense compounds but also various strategies of their application. Protein inhibitors of viruses are a special group of vegetal antibiotic substances. The antiviral activity of a particular inhibitor is usually tested by mixing it with the viral suspension, the mix is used for inoculation of the leaves of a supersusceptible host plant, and then the number of infection spots that occurs is counted. Plant treatment with ribosome inhibitory proteins (RIPs) some time after the inoculation will not prevent development of the viral infection.

A new convenient method for the synthesis of the phosphonic and phosphinic analogues of L-Ala-L-Ala has been developed and their fungicidal activity has been demonstrated.

Aminomethylphosphinic acid, which was found to exhibit fungicidal activity, was synthesised in one step by the interaction of formaldoxime and sodium hypophosphite with HCl.

A polyketide exometabolite — 3,4,8-trihydroxy-3,4-dihydronaphthalen-1(2H)-one (3,4,8-TDH) — has been isolated from the culture liquids of four isolates of the phytopathogenic fungusPiricularia oryzae Cavara. It has been shown that all the natural isolates investigated, and also nonpathogenic rose mutants and a series of dwarf mutants synthesize 3,4,8-TDH. This substance was not detected in filtrates of cultures of albino mutants. One of the natural isolates produces, together with 3,4,8-TDH, another polyketide — piriculol. The role in pathogenesis of the exometabolites isolated is discussed.