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Symptoms of tomato powdery mildew ( O. neolycopersici ) infection on susceptible S. lycopersicum . a The initial symptoms of powdery mildew. b Intensive disease infestation. c Necrosis after intensive disease development. (photo B. Mieslerová) 

Symptoms of tomato powdery mildew ( O. neolycopersici ) infection on susceptible S. lycopersicum . a The initial symptoms of powdery mildew. b Intensive disease infestation. c Necrosis after intensive disease development. (photo B. Mieslerová) 

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Tomato powdery mildew (Oidium neolycopersici) is one of the most devastating diseases of cultivated tomatoes worldwide. Although the first epidemics were recorded more than 25 years ago many aspects of this host-pathogen interaction are still not well understood. Detailed morphological and molecular studies of the anamorphs confirmed that O. neolyc...

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... first symptoms of disease start to appear in early summer, occasionally at the end of spring. The primary symptoms of white circular pustules occur mainly on the upper sides of leaves and often spread onto petioles and stems. The younger leaves are mostly without symptoms. Colonies of powdery mildews are initially small, 3 – 10 mm in average, and then coalesce and finally mycelium can cover the whole leaf (Fig. 2). In severly attacked plants, powdery mildew can be found also on the lower side of leaves, on petioles and stalks; however, it has never been found on fruits. The infected parts of plants grow slower, and often become chlorotic (Mieslerová and Lebeda 1999). The occurrence of the disease is recorded mainly on glasshouse tomato crops although records from the field are also known (Mieslerová and Lebeda ...

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... Previous studies observed specific steps in the infection processes of P. neolycopersici including appressoria [20,48], haustoria [49][50][51][52], and conidiophores [50,[53][54][55] in tomato leaf epidermal cells via histological staining. Such studies typically require chemical treatments (e.g., chlorophyll removal, fixation and staining) to clearly observe morphology (haustoria) and cytological responses (hypersensitive cell death or papillae) in epidermal cells. ...
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... Powdery mildew (PM) in tomato, caused by the obligate biotrophic fungus Oidium neolycopersici (On), is a world-wide disease that threatens the production of greenhouse-and field-grown tomatoes [1,2]. Over the last few decades, research focused on breeding for resistance against PM in tomato has resulted in the identification of five dominant resistance (R) genes (Ol-genes) from wild tomato species [3]. ...
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Background: The development of CRISPR/Cas9 technology has facilitated targeted mutagenesis in an efficient and precise way. Previously, RNAi silencing of the susceptibility (S) gene PowderyMildewResistance 4 (PMR4) in tomato has been shown to enhance resistance against the powdery mildew pathogen Oidium neolycopersici (On). Results: To study whether full knock-out of the tomato PMR4 gene would result in a higher level of resistance than in the RNAi-silenced transgenic plants we generated tomato PMR4 CRISPR mutants. We used a CRISPR/Cas9 construct containing four single-guide RNAs (sgRNAs) targeting the tomato PMR4 gene to increase the possibility of large deletions in the mutants. After PCR-based selection and sequencing of transformants, we identified five different mutation events, including deletions from 4 to 900-bp, a 1-bp insertion and a 892-bp inversion. These mutants all showed reduced susceptibility to On based on visual scoring of disease symptoms and quantification of relative fungal biomass. Histological observations revealed a significantly higher occurrence of hypersensitive response-like cell death at sites of fungal infection in the pmr4 mutants compared to wild-type plants. Both haustorial formation and hyphal growth were diminished but not completely inhibited in the mutants. Conclusion: CRISPR/Cas-9 targeted mutagenesis of the tomato PMR4 gene resulted in mutants with reduced but not complete loss of susceptibility to the PM pathogen On. Our study demonstrates the efficiency and versatility of the CRISPR/Cas9 system as a powerful tool to study and characterize S-genes by generating different types of mutations.
... The relative age of the various organs of host plants can also influence susceptibility to pathogens, especially given the long cropping cycles for fruits and vegetables grown in the greenhouse. For example, leaves of strawberries acquire ontogenic resistance to powdery mildew rapidly after they unfold and thus become more resistant as they age (Asalf et al. 2014;Carisse and Bouchard 2010), while in tomato and pepper, older leaves are more susceptible to powdery mildew (De Souza and Café-Filho 2003;Lebeda et al. 2014). There is also evidence that senescing leaves of tomato are more susceptible to infection by B. cinerea than their younger counterparts, and that infection by this pathogen may accelerate the senescence of infected leaves (Swartzberg et al. 2008). ...
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... In resistant tomato plant genotypes, the pathogen cannot overcome the plants' defence system. In these cases, there is no formation of functional haustoria due to the occurrence of hypersensitivity reactions in the epidermal cells invaded by the pathogen, resulting in the failure of the pathogen infection [18]. Hence, it seems reasonable that the higher accuracy in detecting the infection happened in the initial phase of pathogen recognition. ...
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This work aimed to verify the existence of patterns on the electrophysiological systemic responses of tomato plants inoculated with a pathogenic fungus in an environment with controlled light and temperature. Electrical signalling was measured before and after inoculation in the same plants, and data were analysed with time series techniques and approximate multi-scale entropy (ApEn). Machine learning algorithms were utilised in order to classify data before and after infection throughout the five days of experiments. The obtained results have shown that it is possible to distinguish differences in the plant’s electrome activity before and after the fungus inoculation. In some cases, we have found scale invariance quantified by the power law decay in the distribution histogram. We also found a higher degree of internal organisation quantified by ApEn. The results of the classification algorithms achieved higher accuracy of infection detection at the initial stage of pathogen recognition by the plant. Besides, this study showed evidence that long-distance electrical signalling is likely involved in the plant-pathogen interaction, since signals were obtained in the stem and the inoculum applied on the plant leaves. This might be useful for the early detection of plant infections.
... La cenicilla del jitomate es causada por el hongo patogénico Leveillula taurica. Esta enfermedad es de distribución cosmopolita y se ha reportado que en condiciones de invernadero tiene alta ocurrencia devastando los cultivos de jitomate (Guigón, 2018;Lebeda et al., 2014). Los principales métodos de control de la cenicilla se basan en la resistencia genética y el uso de fungicidas químicos (Kiss, 2003); sin embargo, los cultivares resistentes no siempre son desarrollados con éxito y, además, existen reportes en donde el patógeno ha perdido sensibilidad a los fungicidas químicos (Kiss, 2003). ...
... Upon infection of a susceptible host, O. neolycopersici causes powdery white lesions on the adaxial tomato leaf surface, abaxial surfaces, petioles, and the calyx; only the fruit remains uninfected. Pathogen infection typically affects leaves of the host plant, causing up to 50% yield losses (fruit) as a result of loss of vigour (Roberts, Momol, & Pernezny, 2002), and has caused devastating epidemics from Europe to North and South America, as well as in Asia (Lebeda et al., 2014). At present, chemical control remains the primary method to manage tomato powdery mildew in greenhouse production; however, chemical fungicide application introduces numerous inherent risks, including the development of pathogen resistance and the accumulation of toxic residues in fruit, both of which pose potential risks to the environment (Nakajima & Akutsu, 2014). ...
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Main conclusion The level of resistance induced in different tomato genotypes after β-CRY treatment correlated with the upregulation of defence genes, but not sterol binding and involved ethylene and jasmonic acid signalling. Elicitins, a family of small proteins secreted by Phytophthora and Pythium spp., are the most well-known microbe-associated molecular patterns of oomycetes, a lineage of fungus-like organisms that include many economically significant crop pathogens. The responses of tomato plants to elicitin INF1 produced by Phytophthora infestans have been studied extensively. Here, we present studies on the responses of three tomato genotypes to β-cryptogein (β-CRY), a potent elicitin secreted by Phytophthora cryptogea that induces hypersensitive response (HR) cell death in tobacco plants and confers greater resistance to oomycete infection than acidic elicitins like INF1. We also studied β-CRY mutants impaired in sterol binding (Val84Phe) and interaction with the binding site on tobacco plasma membrane (Leu41Phe), because sterol binding was suggested to be important in INF1-induced resistance. Treatment with β-CRY or the Val84Phe mutant induced resistance to powdery mildew caused by the pathogen Pseudoidium neolycopersici, but not the HR cell death observed in tobacco and potato plants. The level of resistance induced in different tomato genotypes correlated with the upregulation of defence genes including defensins, β-1,3-glucanases, heveins, chitinases, osmotins, and PR1 proteins. Treatment with the Leu41Phe mutant did not induce this upregulation, suggesting similar elicitin recognition in tomato and tobacco. However, here β-CRY activated ethylene and jasmonic acid signalling, but not salicylic acid signalling, demonstrating that elicitins activate different downstream signalling processes in different plant species. This could potentially be exploited to enhance the resistance of Phytophthora-susceptible crops.
... neolycopersici) (L. Kiss) L. Kiss is a disease predominantly devastating glasshouse tomato crops worldwide (Lebeda et al. 2014). A proper understanding of the processes taking part in Solanum spp. ...
... In many host-pathogen interactions, plant resistance and/or susceptibility is influenced by high temperature (Schweizer et al. 1995;Kubienová et al. 2013;Lebeda et al. 2014). Heat stress may modify the level of endogenous concentrations of the chemical compounds that subsequently influence plant resistance/ susceptibility to the pathogen. ...
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The effect of plant heat-shock (HS) pre-treatment (40.5°C, 2 h) on Pseudoidium neolycopersici development in the susceptible and moderately resistant Solanum spp. genotypes was studied together with biochemical responses (endogenous concentrations of salicylic (SA), jasmonic (JA), abscisic acid (ABA), and peroxidase (POX) activity). In HS pre-treated S. lycopersicum, an acceleration of pathogen, chlorosis and necrosis development, strong SA, JA accumulation, and increased POX activity were detected. In S. chmielewskii, HS pre-treatment caused a slight suppression of pathogen development, increase in JA, ABA concentrations, and POX activity. HS accelerated and strengthened the development of symptoms and biochemical responses to the infection in the susceptible genotype in contrast to moderately resistant genotype with a robust defence response to an infection per se.