Lycopersici Infection Research Articles

Impairment of the photorespiratory pathway on tomato leaves during the infection process of Septoria lycopersici

Septoria leaf spot, caused by Septoria lycopersici, is a destructive disease on tomato that reduces fruit quality and yield. Plants infected by pathogens display profound changes in photosynthesis, photorespiration, and respiration that affect defense responses. This study investigated the impacts caused by S. lycopersici infection on the photorespiration of tomato plants. Infected leaves showed a remarkable reduction in photosynthesis and in the pool of photosynthetic pigments. The respiration and photorespiration-to-gross photosynthesis ratio increased in the infected leaves. Reduction in photosynthesis on infected leaves was mainly associated with biochemical limitations. Infection by S. lycopersici resulted in increased concentrations of malonaldehyde, superoxide anion, and hydrogen peroxide indicating great oxidative damage. Genes involved in the photorespiratory pathway (GOX1, GOX2, SHMT2, SMHT3, and GLYK), nitrogen metabolism (Fd-GOGAT), and stress acclimatization (mMDH1, mMDH2, and CAT) were up-regulated during the infection process of S. lycopersici. A better comprehension of the physiological changes in tomato leaves infected by S. lycopersici at the photorespiration level may contribute to breeding cultivars with increased resistance to cope with Septoria leaf spot.

Physiological and biochemical insights into induced resistance on tomato against septoria leaf spot by a phosphite combined with free amino acids

Septoria leaf spot (SLS), caused by Septoria lycopersici, is a destructive disease in tomato. This study investigated the use of phosphite and potassium combined with l-α-free amino acids (named induced resistance (IR) stimulus), to boost tomato defense responses against S. lycopersici infection. Plants were sprayed with water or with the IR stimulus and challenged or not with S. lycopersici. Mycelial growth of S. lycopersici and conidia germination were not affected by the IR stimulus in vitro. Reduction in SLS severity and less leaf tissue colonization by S. lycopersici (lower TEF-1α expression) occurred for IR stimulus-sprayed plants. The IR stimulus-sprayed plants showed lower concentrations of malondialdehyde, hydrogen peroxide, and superoxide anion radical while the concentrations of sucrose, fructose, and starch and activities of ascorbate peroxidase, catalase, glutathione reductase, and superoxide dismutase were great compared to water-sprayed plants in response to S. lycopersici infection. Less impairment on the photosynthetic apparatus not related to biochemical limitations, abrupt increase in transpiration rate, and higher concentrations of chlorophyll a+b and carotenoids occurred for IR stimulus-sprayed plants facing reduced SLS symptoms. Genes involved in host defense reactions (CHI3, CHI9, GLU, PAL3, POX3, PPOB, and PPOF) and those related to systemic acquired resistance (PAL3 and ICS) or induced systemic resistance ((ethylene production - ACO2, ACO3, ACO5, and ACO4) and jasmonic acid signaling pathway (LOX1.1, LOXB, LOXC, and PDF1.2)) were up-regulated for IR stimulus-sprayed and infected plants. These findings highlight the potential of using this IR stimulus for SLS management.

Stemphylium lycopersici Nep1-like Protein (NLP) Is a Key Virulence Factor in Tomato Gray Leaf Spot Disease.

The fungus Stemphylium lycopersici (S. lycopersici) is an economically important plant pathogen that causes grey leaf spot disease in tomato. However, functional genomic studies in S. lycopersici are lacking, and the factors influencing its pathogenicity remain largely unknown. Here, we present the first example of genetic transformation and targeted gene replacement in S. lycopersici. We functionally analyzed the NLP gene, which encodes a necrosis- and ethylene-inducing peptide 1 (Nep1)-like protein (NLP). We found that targeted disruption of the NLP gene in S. lycopersici significantly compromised its virulence on tomato. Moreover, our data suggest that NLP affects S. lycopersici conidiospore production and weakly affects its adaptation to osmotic and oxidative stress. Interestingly, we found that NLP suppressed the production of reactive oxygen species (ROS) in tomato leaves during S. lycopersici infection. Further, expressing the fungal NLP in tomato resulted in constitutive transcription of immune-responsive genes and inhibited plant growth. Through gene manipulation, we demonstrated the function of NLP in S. lycopersici virulence and development. Our work provides a paradigm for functional genomics studies in a non-model fungal pathogen system.

Corynespora cassiicola and Stemphylium lycopersici infection and disease development on tomatoes in Argentina

Two pathogens were isolated from tomatoes with severe chlorosis and necrosis in northwestern Argentina. Monosporic cultures were morphologically characterised and molecularly identified as Stemphylium lycopersici and Corynespora cassiicola. This is the first report of C. cassiicola infecting tomato in Argentina.

Transcriptome Analysis of the Sm-Mediated Hypersensitive Response to Stemphylium lycopersici in Tomato.

Gray leaf spot disease caused by Stemphylium lycopersici is a major disease in cultivated tomato plants and threatens tomato-growing areas worldwide. Sm is a single dominant gene that confers resistance to tomato gray leaf spot disease agent. However, the underlying molecular mechanism remains unclear. Here, resistant (cv. Motelle, containing the Sm gene) and susceptible (cv. Moneymaker) plants were inoculated with virulent Stemphylium lycopersici isolate at a time point at which both cultivars showed a strong response to S. lycopersici infection. Transcriptome analyses were performed in both cultivars using RNA-seq. The number of differentially expressed genes (DEGs) was higher in Motelle than Moneymaker. Functional classification revealed that most DEGs were involved in plant–pathogen interactions, plant hormone signal transduction, regulation of autophagy, glycerophospholipid metabolism, and α-linolenic acid metabolism. Moreover, the genes that were significantly up-regulated in Sm tomatoes were involved in plant–pathogen interaction pathways. A total of 26 genes were selected for confirmation of differentially expressed levels by quantitative real-time PCR. This knowledge will yield new insights into the molecular mechanism of Sm responses to S. lycopersici infection.

Fungal cell wall polymer based nanoparticles in protection of tomato plants from wilt disease caused by Fusarium oxysporum f.sp. lycopersici

Cell wall polymer (chitosan) was isolated from Fusarium oxysporum f.sp. lycopersici. They were cross linked with sodium tripolyphosphate (TPP) to synthesize nanoparticles (CWP-NP). The nanoparticles were characterized by FTIR, DLS, SEM, XRD and NMR analyses. The isolated CWP-NP exhibit antifungal activity under in vitro condition. The foliar application of the CWP-NP to tomato plants challenged with F. oxysporum f. sp. lycopersici showed delay in wilt disease symptom expression and reduce the wilt disease severity. Treated plants also showed enhanced yield. These results suggested the role of the CWP-NP in protecting tomato plants from F. oxysporum f.sp. lycopersici infection.

Phenyl derivative of pyranocoumarin precludes Fusarium oxysporum f.sp. Lycopersici infection in Lycopersicon esculentum via induction of enzymes of the phenylpropanoid pathway.

Binding of phenyl derivative of pyranocoumarin (PDP) modulated activity of fungal endopolygalacturonase in silico. Induced fit docking study of PDP with endopolygalacturonase (1HG8) showed a bifurcated hydrogen bond interaction with the protein at Lys 244 with a docking score of -3.6 and glide energy of -37.30 kcal/mol. Docking with endopolygalacturonase II (1CZF) resulted hydrogen bond formation with Lys 258 with a docking score of -2.3 and glide energy of -30.42 kcal/mol. It was hypothesized that this modulation favors accumulation of cell wall fragments (oligogalacturonides) which act as elicitors of plant defense responses. In order to prove the same, in vivo studies were carried out using a formulation developed from PDP (PDP 5EC) on greenhouse grown Lycopersicon esculentum L. The formulation was effective at different concentrations in reduction of seed infection, improvement of vigor and control of Fusarium oxysporum f.sp. lycopersici infection in L. esculentum. At a concentration of 2 %, PDP 5EC significant reduction in seed infection (95.83 %), improvement in seed vigor (64.31 %) and control of F. oxysporum f.sp. lycopersici infection (96.15 %) were observed. Further application of PDP 5EC to L. esculentum challenged with F. oxysporum f.sp. lycopersici significantly increased the activity of enzymes of the phenylpropanoid pathway, namely, peroxidase (PO), polyphenol oxidase (PPO), phenylalanine ammonia lyase (PAL), and enhanced the total phenolic content when compared to the control.

Differential gene expression, induced by salicylic acid and Fusarium oxysporum f. sp. lycopersici infection, in tomato

The objective of this work was to determine the transcript profile of tomato plants (Lycopersicon esculentum Mill.), during Fusarium oxysporum f. sp. lycopersici infection and after foliar application of salicylic acid. The suppression subtractive hybridization (SSH) technique was used to generate a cDNA library enriched for transcripts differentially expressed. A total of 307 clones was identified in two subtractive libraries, which allowed the isolation of several defense-related genes that play roles in different mechanisms of plant resistance to phytopathogens. Genes with unknown roles were also isolated from the two libraries, which indicates the possibility of identifying new genes not yet reported in studies of stress/defense response. The SSH technique is effective for identification of resistance genes activated by salicylic acid and F. oxysporum f. sp. lycopersici infection. Not only the application of this technique enables a cost effective isolation of differentially expressed sequences, but also it allows the identification of novel sequences in tomato from a relative small number of sequences.

Most AAL toxin-sensitive Nicotiana species are resistant to the tomato fungal pathogen Alternaria alternata f. sp. lycopersici.

The phytopathogenic fungus Alternaria alternata f. sp. lycopersici produces AAL toxins required to colonize susceptible tomato (Lycopersicon esculentum) plants. AAL toxins and fumonisins of the unrelated fungus Fusarium moniliforme are sphinganine-analog mycotoxins (SAMs), which are toxic for some plant species and mammalian cell lines. Insensitivity of tomato to SAMs is determined by the Alternaria stem canker gene 1 (Asc-1), and sensitivity is associated with a mutated Asc-1. We show that SAM-sensitive species occur at a low frequency in the Nicotiana genus and that candidate Asc-1 homologs are still present in those species. In Nicotiana spp., SAM-sensitivity and insensitivity also is mediated by a single codominant locus, suggesting that SAM-sensitive genotypes are host for A. alternata f. sp. lycopersici. Nicotiana umbratica plants homozygous for SAM-sensitivity are indeed susceptible to A. alternata f. sp. lycopersici. In contrast, SAM-sensitive genotypes of Nicotiana spegazzinii, Nicotiana acuminata var. acuminata, Nicotiana bonariensis, and Nicotiana langsdorffii are resistant to A. alternata f. sp. lycopersici infection concomitant with localized cell death. Additional (nonhost) resistance mechanisms to A. alternata f. sp. lycopersici that are not based on an insensitivity to SAMs are proposed to be present in Nicotiana species.

Effects of Pyrenochaeta lycopersici infection on nutrient uptake by tomato plants

SUMMARYThe growth of young tomato plants in nutrient solution or in soil and infected with Pyrenochaeta lycopersici Schneider & Gerlach, the cause of tomato brown root rot, was decreased relative to that of uninfected plants. The roots of plants grown in nutrient solution and infected with a mycelial mat of the pathogen contained lower concentrations of potassium and higher concentrations of calcium than roots of uninfected plants. These changes occurred largely in the visibly affected tissue, as opposed to the root system as a whole. The concentrations of magnesium, total nitrogen and phosphorus in the roots of infected plants were not significantly different from those of control plants.Magnesium, nitrogen and phosphorus concentrations in the tops of infected plants were also not significantly different from those of healthy plants, but no consistent changes were found in the concentrations of calcium and potassium.Young tomato plants grown in soil infested with P. lycopersici contained lower concentrations of phosphorus and potassium in the tops than plants grown in sterilized soil. It was not possible to separate intact damaged root systems of infected plants from soil.The changes in composition found in infected plants are discussed in relation to possible methods of manipulating the nutrition of the plant to offset the effects of the disease on crop yield.