Franco Gozzo

Systemic acquired resistance (50 years after discovery): moving from the lab to the field.

Induction of plant defense(s) against pathogen challenge(s) has been the object of progressively more intense research in the past two decades. Insights on mechanisms of systemic acquired resistance (SAR) and similar, alternative processes, as well as on problems encountered on moving to their practical application in open field, have been carefully pursued and, as far as possible, defined. In reviewing the number of research works published in metabolomic, genetic, biochemical, and crop protection correlated disciplines, the following outline has been adopted: 1, introduction to the processes currently considered as models of the innate immunity; 2, primary signals, such as salicylic acid (SA), jasmonic acid (JA), and abscisic acid (ABA), involved with different roles in the above-mentioned processes; 3, long-distance signals, identified from petiole exudates as mobile signaling metabolites during expressed resistance; 4, exogenous inducers, including the most significant chemicals known to stimulate the plant resistance induction and originated from both synthetic and natural sources; 5, fungicides shown to act as stimulators of SAR in addition to their biocidal action; 6, elusive mechanism of priming, reporting on the most recent working hypotheses on the pretranscriptional ways through which treated plants may express resistance upon pathogen attack and how this resistance can be transmitted to the next generation; 7, fitness costs and benefits of SAR so far reported from field application of induced resistance; 8, factors affecting efficacy of induced resistance in the open field, indicating that forces, unrevealed under controlled conditions, may be operative in the field; 9, concluding remarks address the efforts required to apply the strategy of crop resistance induction according to the rules of integrated pest management.

Effects of a triazolic fungicide on maize plant metabolism: modifications of transcript abundance in resistance-related pathways

Using a molecular approach, the effects of tetraconazole (TC), a triazolic inhibitor of P-450-based enzymes, has been investigated in maize, focusing on the resistance-related biosynthetic pathways involving one or more microsomial P-450 mono-oxigenases, putative secondary targets of the fungicide. Several observations were made. First, TC affected the phenylpropanoid-flavonoid biosynthesis, increasing the anthocyanin content and the mRNA abundance of the genes involved in the later steps of the pathway (A1 and C2), while the expression of another gene, PAL, decreased in the roots. Second, the activity of a hydroxyproline-rich glycoprotein gene involved in root cell wall structures was enhanced. Finally, maize seedlings acquired increased resistance to drought, which corresponded with modified levels of abscissic acid (ABA) and the overexpression of an ABA regulated gene. Taken together, these results suggest that TC act as a potential activator of plant defence-responses to both abiotic and biotic challenges and represents a powerful tool for elucidating the regulatory interconnections between different biosynthetic pathways.

Is modulating virus virulence by induced systemic resistance realistic

Induction of plant resistance, either achieved by chemicals (systemic acquired resistance, SAR) or by rhizobacteria (induced systemic resistance, ISR) is a possible and/or complementary alternative to manage virus infections in crops. SAR mechanisms operating against viruses are diverse, depending on the pathosystem, and may inhibit virus replication as well as cell-to-cell and long-distance movement. Inhibition is often mediated by salicylic acid with the involvement of alternative oxidase and reactive oxygen species. However, salicylate may also stimulate a separate downstream pathway, leading to the induction of an additional mechanism, based on RNA-dependent RNA polymerase 1-mediated RNA silencing. Thus, SAR and RNA silencing would closely cooperate in the defence against virus infection. Despite tremendous recent progress in the knowledge of SAR mechanisms, only a few compounds, including benzothiadiazole and chitosan have been shown to reduce the severity of systemic virus disease in controlled environment and, more modestly, in open field. Finally, ISR induction, has proved to be a promising strategy to control virus disease, particularly by seed bacterization with a mixture of plant growth-promoting rhizobacteria. However, the use of any of these treatments should be integrated with cultivation practices that reduce vector pressure by the use of insecticides, or by Bt crops.

Comparative antifungal effect and mode of action of tetraconazole on Ustilago maydis

Abstract Tetraconazole, a new, recently introduced antifungal triazole, has been assayed in parallel with a number of standard analogues on various sensitive strains of Ustilago maydis. The values of EC50 and EC90 tetraconazole concentrations, determined on strain ATCC 14826 in agar, were 0.5 × 10−6 and 3.5 × 10−5 m , respectively, in reasonable agreement with those needed to inhibit by 50% and 90%, respectively, the ergosterol biosynthesis in broth cultures. Squalene and 12 sterols have been extracted from the latter, characterized and quantified. Accumulation of 14α-methylsterols and reduction of ergosterol and other late precursors are consistent with the inhibition of 14α-demethylase caused by the title compound.

Characterization of field-isolates and derived DMI-resistant strains of Cercospora beticola

Cercospora beticola strains with laboratory induced resistance to tetraconazole were compared with their parental WT sensitive strains to evaluate the effects of resistance on fitness and assess whether any change in the sterol biosynthetic pathway was associated to the reduced fungicide sensitivity. In vitro growth rate on agar media and pathogenicity were found to be negatively affected by resistance. The main functional sterols in C. beticola WT strains under investigation were ergosterol, brassicasterol and ergosta-7,22-dienol. Resistant strains showed the same qualitative sterol composition, ruling it out as, per se, a cause for resistance. On the basis of the sterols detected both in sensitive and resistant strains, a possible biosynthetic pathway to the three functional sterols is proposed. Tetraconazole treatment caused, in all sensitive strains, the immediate accumulation of 14alpha-methylated sterols, which, for inhibitor concentrations up to EC50 values, were, in order of abundance, 14alpha-methylergosta-8,24(28)-dien-3beta,6alpha-diol, eburicol and obtusifoliol. However the data do not support a critical role of the 14-methyl-3,6-diol derivative in the growth arrest of C. beticola. As main difference between sensitive and resistant strains, the formers were found to accumulate higher amounts of 14alpha-methylated sterols. Although the data do not allow to establish a specific mechanism for resistance, some molecular mechanisms such as target site alterations and sterol biosynthetic pathway can be ruled out as a possible cause for reduced sensitivity.

Chemical evidence of the effects of mancozeb on benalaxyl in grape plants as possible rationale for their synergistic interaction

Abstract The fate of [ 14 C]benalaxyl as affected by mancozeb has been determined on the surface and in tissues of grape leaves 7 days after a single foliar application of the mixture. A first effect of mancozeb was a substantial reduction of the uptake of benalaxyl by the leaves. In spite of that, the amount of benalaxyl inside the leaves was a little higher than when it was separately applied. This was the consequence of the second effect of mancozeb resulting in a delayed metabolism of the systemic partner. Although the nature of the metabolites was totally unaffected, their amount was in fact markedly reduced by the mixture. This finding is discussed as a possible rationale for the mechanism of the synergistic interaction.

The logic of cereal disease control with antifungal azoles

Abstract Quantitative structure-activity relationships have been performed by applying the Hansch approach to a series of known and new antifungal azoles, mainly 1,2,4-triazole derivatives, in their control of two diseases, caused by Erysiphe graminis and Puccinia graminis , on wheat plants. The residual protective control of E. graminis may be expressed as a linear function of a single parameter, represented by log P air/water , calculated by available data of solubility and vapor pressure at 20°C. The curative action against P. graminis follows a more complex logic and requires multiparametric equations. The related EC 80 values could be expressed as a linear function of the difference (log P air/water − log P octanol/water ) = log P air/octanol , provided two dummy parameters were added to formally account for the presence of H-donor and H-acceptor groups present in the side chain of the azoles. The uncertainty associated with the latter of these parameters is discussed and tentatively ascribed to a possible masking of electrostatic potential associated with electronegative groups. The different complexity in the control of the two pathogens is thought to mainly depend on the different location of the related mycelia.