Infected Tomato Plants Research Articles

A comparison of induced antiviral resistance by the phytoprotein CAP-34 and isolate P1f of the rhizobacterium Pseudomonas putida.

CAP-34 is a previously reported phytoprotein isolated from Clerodendrum aculeatum (syn. Volkameria aculeata), inducing systemic antiviral resistance against plant virus infection in susceptible plants. This paper compares the resistance inducing efficacy of CAP-34 and a rhizobacterial isolate P1f on tomato (systemic) and tobacco Xanthi-nc (hypersensitive), against tobacco mosaic virus (TMV). The PGPR isolate was identified as an isolate of Pseudomonas putida through molecular and biochemical characterization, and it exhibited PGPR traits such as production of auxin and siderophore. GC-MS examination of the volatiles produced by P1f included several that are implicated in antimicrobial activity, growth promotion and induced systemic resistance. Foliar treatment of tobacco plants with P1f and CAP-34 led to an induced antiviral state in hypersensitive tobacco that persisted for 5 and 3days, post-treatment, respectively, with a percent reduction in lesion number greater than 90. A higher accumulation of hydrogen peroxide and production of peroxidase enzyme was recorded in P1f-treated leaves, in comparison to those with CAP-34 treatment. The disease incidence in tomato plants treated with CAP-34 and P1f was 30 and 60 percent, respectively, 28dpi. A significant increase was noted in growth parameters such as number of branches and flowers in CAP-34 treated plants, while a significant enhancement in plant height and dry shoot and root weight was observed in P1f-treated set, compared to the control set. ELISA values for the presence of TMV were significantly lower in the infected tomato plants in the treated sets, as compared to the control set, with CAP-34 treatment exhibiting better results as against the P1f-treated set. In the resistant plants from either set, no viral RNA or viral coat protein was detected through RT-PCR and serology. These results suggest that CAP-34 affords more pronounced protection against virus infection compared to the rhizobacterial isolate P1f.

Green Synthesis of Silver Nanoparticles Using Pomegranate and Orange Peel Extracts and Their Antifungal Activity against Alternaria solani, the Causal Agent of Early Blight Disease of Tomato.

This study aimed to synthesize silver nanoparticles (AgNPs) by pomegranate and orange peel extracts using a low concentration of AgNO3 solution to controlearly blight of tomato caused by Alternaria solani. The pathogen was isolated from infected tomato plants growing in different areas of Saudi Arabia. The isolates of this pathogen were morphologically and molecularly identified. Extracts from peels of pomegranate and orange fruits effectively developed a simple, quick, eco-friendly and economical method through a synthesis of AgNPs as antifungal agents against A. solani. Phenolic content in the pomegranate peel extract was greater than orange peel extract. Phenolic compounds showed a variation of both peel extracts as identified and quantified by High-Performance Liquid Chromatography. The phenolic composition displayed variability as the pomegranate peel extract exhibited an exorbitant amount of Quercitrin (23.62 mg/g DW), while orange peel extract recorded a high amount of Chlorogenic acid (5.92 mg/g DW). Biosynthesized AgNPs were characterized using UV- visible spectroscopy which recorded an average wavelength of 437 nm and 450 nm for pomegranate and orange peels, respectively. Fourier-transform infrared spectroscopy exhibited 32x73.24, 2223.71, 2047.29 and 1972.46 cm−1, and 3260.70, 1634.62, 1376.62 and 1243.76 cm−1 for pomegranate and orange peels, respectively. Transmission electron microscopy showed spherical shape of nanoparticles. Zetasizer analysis presented negative charge values; −16.9 and −19.5 mV with average particle sizes 8 and 14 nm fin case of pomegranate and orange peels, respectively. In vitro, antifungal assay was done to estimate the possibility of biosynthesized AgNPs and crude extracts of fruit peels to reduce the mycelial growth of A. solani. AgNPs displayed more fungal mycelial inhibition than crude extracts of two peels and AgNO3. We recommend the use of AgNPs synthesized from fruit peels for controlling fungal plant pathogens and may be applied broadly and safely in place by using the chemical fungicides, which display high toxicity for humans.

Ethyl acetate extract of Streptomyces spp. isolated from Egyptian soil for management of Fusarium oxysporum: The causing agent of wilt disease of tomato

Tomato crops faced dangerous problems due to their attack by Fusarium oxysporum f. sp. lycopersici , the causing agent of wilt disease. Chemical treatments of such diseases caused many hazardous impacts to soil and human. For this reason, the biological control is considered as an alternative and sustainable tool for curing several plant diseases. The present work is undertaken with the aim of treating Fusarium -contaminated tomato seeds with ethyl acetate extracts from isolated Steptomyces spp., in greenhouse studies. Fifteen Steptomyces spp., isolated from native tomato rhizospheric soils, were evaluated for their antagonistic potential against Fusarium wilt pathogen . Three isolates that exhibited higher antagonistic effect were molecularly identified. Their ethyl acetate extracts (EAE) exhibited antifungal activity against the target pathogen, with higher potential with S. carpaticus EGY-S7 strain. Greenhouse assay indicated that seed treatment by the selected EAE of Steptomyces spp., isolates significantly reduced disease severity and possessed seedlings growth promoting potential of tomato ranging from 72.6 to 83.0% compared to infected control (63.4%) and chemical fungicide (76.2%). Accordingly, strain S. carpaticus EGY-S7 showed higher control efficacy (83.0%) as well as significantly increased the biomass of tomato seedlings (plant height, leaves number, fresh and dry weight) compared to a positive control (with infested soil). Additionally, it was superior to other strains, in which total polyphenols, polyphenoloxidase and peroxidase enzymes were significantly enhanced in tomato seedlings compared with untreated-infected control. Gas chromatography-mass spectrometry (GC-MS) analysis of EAE derived from S. carpaticus EGY-S7 strain was also identified. • Isolation of the fungal pathogens ( Fusarium spp.) from infected tomato plants. • Isolation of Streptomyces spp. from the surroundings soil of infected plants. • Measuring the antagonistic effect between isolates. • Production of bioactive compounds from Streptomyces spp. • Studying the effect of Streptomyces spp. extracts on the growth of tomato seedlings.

An anomalous detection of Tomato yellow leaf curl virus in tomato in New York State.

In August 2020, a New York State vegetable grower sought assistance to identify a malady of tomato (Solanum lycopersicum). The plants were grown from saved seed that had been planted annually in NY and/or FL for over 15 years without significant disease problems, but the identity of the cultivar was not known. Submitted photos showed severely stunted plants with distorted leaves (crinkling, cupping, twisting); leaves were reduced in size and showed interveinal yellowing. Although the most likely explanation given the growing region was herbicide damage, the symptoms bore a striking resemblance to those presented by tomato yellow leaf curl (TYLCV)-infected tomato plants. TYLCV has not been reported from NY, as the whitefly vector (Bemisia tabaci) does not overwinter in the region. Stem tissue from a symptomatic plant was grafted onto a greenhouse grown rootstock of tomato breeding line 201231 (Cornell University); shoots emerging from grafted rootstocks showed symptoms consistent with those on the scion within 21 days of grafting. Total nucleic acid was extracted (Gambino et al. 2008), and a polymerase chain reaction (PCR) assay to detect TYLCV was performed using primers AV632 and AC1048 (Martínez-Culebras et al. 2001). Sanger sequencing of the expected size ~460 bp product from a representative sample showed 98% nucleotide identity with the sequence of over 52 isolates of TYLCV (blastn analysis using default parameters; Altschul et al. 1990). The total nucleic acid preparation was subjected to rolling circle ampification followed by restriction enzyme SphI digestion (Haible et al. 2006). An approximately 2.8 kb DNA fragment was resolved by agarose gel electrophoresis, gel purified, inserted into the cloning vector pUC19 and sequenced. Two clones yielded sequence of 2781 nt with only one nt mismatch (accession # MW373746, MW373747). BLAST analysis showed the sequence to be most closely related to TYLCV-IL from papaya in Texas (accession KX024647.1) with 99% identity (2752 of 2781 nt). Further inquiry revealed that the vegetable grower's plants had been seeded and grown in Florida prior to transplanting in NY; Florida is a production region where the virus and vectors are endemic. Although the virus has been shown to be associated with seed (Pérez-Padilla et al. 2020) and seed transmission has been reported (Kil et al. 2016), this subject is controversial and the epidemiology of the disease is not consistent with a seed-transmitted virus (Rojas, et al. 2018). In this reported occurrence, the most plausible explanation is that the virus was introduced into NY with transplants. All of the field grown transplants of this cultivar were infected, but no local disease spread in NY was reported, nor were there reports of the vector. The significance of this report is to highlight the importance of phytosanitation in the movement of plants and plant materials. The long-distance movement of TYLCV via infected transplants in the US and globally is well-established. The presence of a pathogen may be transient and their establishment will depend on the epidemiology of the pathogen, in this case, the presence of the vector.

Occurrence of Pseudomonas fluorescens and P. putida associated to tomato pith necrosis in Brazil

ABSTRACT In 2016, several reports emerged of fresh-market staked tomato plants with severe symptoms of pith necrosis and premature death in commercial cultivation areas in the states of Paraná and Minas Gerais, Brazil, which are similar to those caused by Pseudomonas corrugata. Four bacterial strains were isolated from infected tissue samples and characterized as Gram-negative, aerobic, and fluorescent on King’s B Medium. LOPAT tests were performed and the isolate UFU H120 was classified into group Vb (+ + − + −) and the isolates UFU H3, UFU H6, and UFU H21 into group Va (− + − + −). The pathogenicity of the isolates was confirmed by artificial inoculation on tomato plants of Santa Cruz type, cv. Kada Gigante, and Koch’s postulates were accomplished successfully. The isolates sequences of their 16S rRNA gene region were compared with those deposited in GenBank, the isolate UFU H120 aligning with Pseudomonas fluorescens (99,45% similarity) and the isolates UFU H3, UFU H6, and UFU H21 with Pseudomonas putida (99.2, 99.53 and 99.64% similarity, respectively). Notably, P. fluorescens and P. putida are most known as saprophytic bacteria normally present in the soil, although both of these species have already been reported to infect tomato plants in Italy. However, so far, there have not been any reports of such bacteria being phytopathogenic on tomato or any crop in Brazil. Thus, to our knowledge, this is the first report of pith necrosis of such occurrence in Brazil.

Molecular studies on Tomato Yellow Leaf Curl Virus in Infected Tomato and Pepper Plants

Molecular studies on Tomato Yellow Leaf Curl Virus in Infected Tomato and Pepper Plants

Controlling Alternaria cerealis MT808477 Tomato Phytopathogen by Trichoderma harzianum and Tracking the Plant Physiological Changes.

Plant responses during the pathogen infection and the pathogen control reflect its strategies to protect its cells. This work represents the Alternaria cerealis MT808477 as a phytopathogen causing leaf spot disease in tomatoes. A. cerealis was identified morphologically and genetically by 18SrRNA, and its pathogenicity was confirmed by light and scanning electron microscopy. Trichoderma harzianum has the ability to control A. cerealis MT808477 by stimulating various cell responses during the controlling process. The cell behavior during the biological control process was observed by analyses of total phenol, flavonoids, terpenoids, antioxidant, malondialdehyde and antioxidant enzymes (catalase and peroxidase). The extracts of infected tomato leaves were tested against plant and human pathogenic microorganisms. Results showed that the biological control process activates the defense cell strategies by increasing the plant tolerance, and activation of plant defense systems. The total phenol, flavonoids, terpenoids, antioxidant and malondialdehyde were increased after 48 h. Catalase and peroxidase were increased in infected tomato plants and decreased during the biological control process, reflecting the decrease of cell stress. Leaves extract inhibited the growth of nine plant and human pathogenic microorganisms. Biological control represents a safe and effective solution to phytopathogens that decreases plant cell stress by stimulating various defensive agents.

Nematicidal Activity of some Nanoemulsions of Monoterpenes on Tomato Root-Knot Nematodes (Meloidogyne javanica)

The present study was initiated to explore at the nematicidal activity of some nanoemulsions of monoterpenes, i.e. (R)-carvone, cinnamaldehyde, citral, geraniol and pulegone against tomato knot-root nematode M. javanica, in both laboratory and under greenhouse conditions The results show that the pure and NE-monoterpenes tested considerably and severely decreased egg hatching at doses ranging from 25 to 1000 μg/ml. NE-Cinnamaldehyde, significantly, showed higher J2 mortality (90.67 %) and egg-hatching inhibition (8.67) than pure cinnamaldehyde. The most successful therapy for reducing root galls and the number of egg masses was NE- Cinnamaldehyde, which showed 90.3% and 92.8% reduction, followed by NE- Pulegone 84.2% reduction, respectively. The population of J2 in soil was considerably decreased after using the tested nanoemulsion monoterpenes. NE- Cinnamaldehyde was the most effective treatment, suppressing the final population of M. javanica by 81.8%. Beyond oxamyl, NE-Cinnamaldehyde was the most efficient treatment for increasing the weights and lengths of both fresh shoots and roots in infected tomato plants, consecutively. Meanwhile, pulegone measured the intermediate values of fresh root and shoot weights as well as for lengths. Normal and nanoemulsion cinnamaldehyde ranked the first as it increased polyphenoloxidase (PPO) activity, compared to the other treatments followed by nanoemulsion and normal pulegone. The highest enzyme activity was noticed 7 and 15 days after treatment. Peroxidase activity (POD) also increased by nanoterpene treatments in a trend similar to that of the PPO. Consequently, these effective monoterpene nanoemulsions could be effective potentially and environmentally safe to control tomato knot-root nematode.

HPE1, an Effector from Zebra Chip Pathogen Interacts with Tomato Proteins and Perturbs Ubiquitinated Protein Accumulation.

The gram-negative bacterial genus Liberibacter includes economically important pathogens, such as ‘Candidatus Liberibacter asiaticus’ that cause citrus greening disease (or Huanglongbing, HLB) and ‘Ca. Liberibacter solanacearum’ (Lso) that cause zebra chip disease in potato. Liberibacter pathogens are fastidious bacteria transmitted by psyllids. Pathogen manipulation of the host’ and vector’s immune system for successful colonization is hypothesized to be achieved by Sec translocon-dependent effectors (SDE). In previous work, we identified hypothetical protein effector 1 (HPE1), an SDE from Lso, that acts as a suppressor of the plant’s effector-triggered immunity (ETI)-like response. In this study, using a yeast two-hybrid system, we identify binding interactions between tomato RAD23 proteins and HPE1. We further show that HPE1 interacts with RAD23 in both nuclear and cytoplasmic compartments in planta. Immunoblot assays show that HPE1 is not ubiquitinated in the plant cell, but rather the expression of HPE1 induced the accumulation of other ubiquitinated proteins. A similar accumulation of ubiquitinated proteins is also observed in Lso infected tomato plants. Finally, earlier colonization and symptom development following Lso haplotype B infection are observed in HPE1 overexpressing plants compared to wild-type plants. Overall, our results suggest that HPE1 plays a role in virulence in Lso pathogenesis, possibly by perturbing the ubiquitin-proteasome system via direct interaction with the ubiquitin-like domain of RAD23 proteins.

Trichoderma-Enriched Vermicompost Extracts Reduces Nematode Biotic Stress in Tomato and Bell Pepper Crops

Root-knot nematode (RKN) is a serious threat to crops worldwide due to the difficulty in controlling it and the limited eco-friendly alternatives to deal with the biotic stress it causes. In the present work, water-extractable fractions obtained from vermicompost (WSFv), vermicompost enriched with Trichoderma asperellum (WSFta) and T. virens (WSFtv) were tested as biotechnological tools to reduce the impacts of RKN on gas exchange, water use efficiency (WUE) and nutrient concentration in tomato and bell pepper plants. The plants were infected with 5000 eggs and eventual J2 of RKN and then treated with the water-extractable fractions for seven weeks. It was observed that the addition of WSFta, WSFtv and WSFv increased the CO2 assimilation, stomatal conductance and WUE in the tomato plants. In the bell pepper plants, WSFta, WSFtv, WSFv increased the stomatal conductance, while WUE was higher in the treatment with WSFtv. In fact, the parameters associated with the gas exchange were usually higher in the bell pepper than in the tomato plants. Overall, higher contents of N, Mg, B and Mn were detected when the extracts were applied in both bell pepper and tomato plants. The application of the water-extractable fractions, inoculated or not with Trichoderma, attenuates the RKN damage on the gas exchange parameters and successfully enhanced the nutrient concentration in the infected tomato and bell pepper plants, showing that it could be an important and promising tool for reducing the damage caused by this pathogen. We suggest that both the tomato and pepper plants can cope with the dilemma between growth and stress response via stomata regulation that are modulated by the WSF and Trichoderma.

Identification of genetic determinants of tomato brown rugose fruit virus that enable infection of plants harbouring the Tm-22 resistance gene.

Tomato cultivars containing the Tm‐22 resistance gene have been widely known to resist tobacco mosaic virus (TMV) and tomato mosaic virus. Tomato brown rugose fruit virus (ToBRFV), a new emerging tobamovirus, can infect tomato plants carrying the Tm‐22 gene. However, the virulence determinant of ToBRFV that overcomes the resistance conferred by the Tm‐22 gene remains unclear. In this study, we substituted the movement protein (MP) encoding sequences between ToBRFV and TMV infectious clones and conducted infectivity assays. The results showed that MP was the virulence determinant for ToBRFV to infect Tm‐22 transgenic Nicotiana benthamiana plants and Tm‐22 ‐carrying tomato plants. A TMV MP chimera with amino acid residues 60–186 of ToBRFV MP failed to induce hypersensitive cell death in the leaves of Tm‐22 transgenic N. benthamiana plants. Chimeric TMV containing residues 60–186 of ToBRFV MP could, but chimeric ToBRFV containing 61–187 residues of TMV MP failed to infect Tm‐22 transgenic N. benthamiana plants, indicating that 60–186 residues of MP were important for ToBRFV to overcome Tm‐22 gene‐mediated resistance. Further analysis showed that six amino acid residues, H67, N125, K129, A134, I147, and I168 of ToBRFV MP, were critical in overcoming Tm‐22 ‐mediated resistance in transgenic N. benthamiana plants and tomato plants. These results increase our understanding of the mechanism by which ToBRFV overcomes Tm‐22 ‐mediated resistance.

Raman Spectroscopy and Machine-Learning for Early Detection of Bacterial Canker of Tomato: The Asymptomatic Disease Condition.

Bacterial canker of tomato is caused by Clavibacter michiganensis subsp. michiganensis (Cmm). The disease is highly destructive, because it produces latent asymptomatic infections that favor contagion rates. The present research aims consisted on the implementation of Raman spectroscopy (RS) and machine-learning spectral analysis as a method for the early disease detection. Raman spectra were obtained from infected asymptomatic tomato plants (BCTo) and healthy controls (HTo) with 785 nm excitation laser micro-Raman spectrometer. Spectral data were normalized and processed by principal component analysis (PCA), then the classifiers algorithms multilayer perceptron (PCA + MLP) and linear discriminant analysis (PCA + LDA) were implemented. Bacterial isolation and identification (16S rRNA gene sequencing) were realized of each plant studied. The Raman spectra obtained from tomato leaf samples of HTo and BCTo exhibited peaks associated to cellular components, and the most prominent vibrational bands were assigned to carbohydrates, carotenoids, chlorophyll, and phenolic compounds. Biochemical changes were also detectable in the Raman spectral patterns. Raman bands associated with triterpenoids and flavonoids compounds can be considered as indicators of Cmm infection during the asymptomatic stage. RS is an efficient, fast and reliable technology to differentiate the tomato health condition (BCTo or HTo). The analytical method showed high performance values of sensitivity, specificity and accuracy, among others.

Infectious Clones of Tomato Chlorosis Virus: Toward Increasing Efficiency by Introducing the Hepatitis Delta Virus Ribozyme.

Tomato chlorosis virus (ToCV) is an emergent plant pathogen that causes a yellow leaf disorder in tomato and other solanaceous crops. ToCV is a positive-sense, single stranded (ss)RNA bipartite virus with long and flexuous virions belonging to the genus Crininivirus (family Closteroviridae). ToCV is phloem-limited, transmissible by whiteflies, and causes symptoms of interveinal chlorosis, bronzing, and necrosis in the lower leaves of tomato accompanied by a decline in vigor and reduction in fruit yield. The availability of infectious virus clones is a valuable tool for reverse genetic studies that has been long been hampered in the case of closterovirids due to their genome size and complexity. Here, attempts were made to improve the infectivity of the available agroinfectious cDNA ToCV clones (isolate AT80/99-IC from Spain) by adding the hepatitis delta virus (HDV) ribozyme fused to the 3′ end of both genome components, RNA1 and RNA2. The inclusion of the ribozyme generated a viral progeny with RNA1 3′ ends more similar to that present in the clone used for agroinoculation. Nevertheless, the obtained clones were not able to infect tomato plants by direct agroinoculation, like the original clones. However, the infectivity of the clones carrying the HDV ribozyme in Nicotiana benthamiana plants increased, on average, by two-fold compared with the previously available clones.

Mycotoxin Profile and Phylogeny of Pathogenic Alternaria Species Isolated from Symptomatic Tomato Plants in Lebanon.

The tomato is one of the most consumed agri-food products in Lebanon. Several fungal pathogens, including Alternaria species, can infect tomato plants during the whole growing cycle. Alternaria infections cause severe production and economic losses in field and during storage. In addition, Alternaria species represent a serious toxicological risk since they are able to produce a wide range of mycotoxins, associated with different toxic activities on human and animal health. Several Alternaria species were detected on tomatoes, among which the most important are A. solani, A. alternata, and A. arborescens. A set of 49 Alternaria strains isolated from leaves and stems of diseased tomato plants were characterised by using a polyphasic approach. All strains were included in the recently defined phylogenetic Alternaria section and grouped in three well-separated sub-clades, namely A. alternata (24 out of 49), A. arborescens (12 out of 49), and A. mali morpho-species (12 out of 49). One strain showed high genetic similarity with an A. limoniasperae reference strain. Chemical analyses showed that most of the Alternaria strains, cultured on rice, were able to produce alternariol (AOH), alternariol methyl ether (AME), altenuene (ALT) and tenuazonic acid (TA), with values up to 5634, 16,006, 5156, and 4507 mg kg−1, respectively. In addition, 66% of the strains were able to co-produce simultaneously the four mycotoxins investigated. The pathogenicity test carried out on 10 Alternaria strains, representative of phylogenetic sub-clades, revealed that they were all pathogenic on tomato fruits. No significant difference among strains was observed, although A. alternata and A. arborescens strains were slightly more aggressive than A. mali morpho-species strains. This paper reports new insights on mycotoxin profiles, genetic variability, and pathogenicity of Alternaria species on tomatoes.

Genetic diversity of tomato yellow leaf curl virus isolates and the effect of virus on the hormones content of tomato (Solanum lycopersicum) plants

Tomato yellow leaf curl virus (TYLCV) is one of the most economically important plant viruses globally and due to its continuing quick spread, now it afflicts many tomato growing countries in the Mediterranean basin, Africa, southern Asia, as well as South, Central and North America. Infection of tomato plants with TYLCV can reach 100% causing a severe reduction in tomato production, especially when plants are infected in the early stage of growth. Therefore, this study was conducted, during the growing season 2018-19 at the college of Agriculture, Kerbala University, Iraq, to isolate and diagnose three different isolates of TYLCV, infecting tomato, using the polymerase chain reaction technology (PCR) and determining the nucleotide sequences of PCR- amplified products and the effect of TYLCV infection on the plant contents of some hormones (gibberellin, cytokinin, and Indole acetic acid). Results of PCR amplification showed the possibility of amplifying a 789bp PCR product from each virus isolate (1, 2, 3, and 4). Analysis of the nucleotide sequences of PCR products using BLAST showed that all the diagnosed isolates belong to TYLCV. By comparing the sequences of nucleotide sequences, there was a genetic similarity of 100% among these isolates. However, all tomato genotypes tested in this study were found to be susceptible to TYLCV with different degrees of infection. TYLCV infection also had a significant effect in reducing the level of the hormone gibberellin in the infected genotypes. Increased levels of the cytokinin and indole acetic acid hormones were also observed in the TYLCV-infected genotypes.

Robust molecular detection of the new Tomato brown rugose fruit virus in infected tomato and pepper plants from Turkey

Tomato brown rugose fruit virus (ToBRFV) causes severe fruit loss in tomato (Solanum lycopersicum) and pepper (Capsicum annuum) plants. It is an emerging Tobamovirus that is spreading globally. The major challenge is to develop a reliable method for the detection of the virus, and to better characterize the symptoms it causes. The aims of this study, therefore, were to characterize the symptom development on tomato and pepper plants, and to establish a reliable detection method for the virus. Following infection of the tomato and pepper plants with ToBRFV, the leaves turned chlorotic, mosaic or mottled, while the fruit became rugose, necrotic and marbled, and showed discoloration with yellow or brown spots. Transmission electron microscopy (TEM) revealed single rod-like virus particles characteristic of the Tobamoviruses. Classical reverse transcription PCR (RT-PCR) and quantitative PCR (qPCR) with specific primers and probes confirmed that the virus is ToBRFV. We found that the resistance genes from tomato, Tm-22, and pepper, L1, L2, L3 and L4, did not confer resistance to ToBRFV. Here, we present a PCR-based method as a diagnostic test for detecting ToBRFV in infected seeds. This method will help to prevent further spread of the virus in commercial seeds.

Topical delivery of host induced RNAi silencing by layered double hydroxide nanosheets: An efficient tool to decipher pathogenicity gene function of Fusarium crown and root rot in tomato

RNAi technique was used to regulate Fusarium crown and root rot in tomatoes caused by F. oxysporum f. sp. radicis-lycopersici (FORL), by targeting three essential genes namely FoCYP51, FoChs1, and FoEF2, considering the fungicide site of action. The designed naked dsRNA was delivered on a hexagonal mono-dispersed and biodegradable layered double hydroxide (LDH) nanosheets with 30–90 nm diameter, providing high protection and stability for dsRNA with long term sustained release manner inside plant cells. The laboratory findings revealed the functional role of the three selected genes in reducing FORL's invasive growth on tomato fruits, indicating their involvement in FORL pathogenesis on tomatoes, and could be good targets for disease control using RNAi. Three different practical methods were applied for topical delivery of dsRNA into the plant cells: i) leaves spray; ii) petiole adsorption; and iii) root dipping, demonstrating three significant levels of spray-induced gene silencing (SIGS) efficacy in controlling FORL virulence infecting tomato plants. Significantly, topical spray of dsRNA delivered on LDH nanosheets provided Fusarium crown and root rot protection for at least 60 days. Obtained findings introduce critical information data on the potential to exploit spray-induced gene silencing (SIGS) as an effective alternative sustainable strategy for plant disease management. Given the ease design and production of biodegradable nano-delivery systems with high specificity and sustainability, and ease of applicability against many disease caused fungi. The use of target-specific dsRNA as an anti-fungal agent has a lot of promise and provide exceptional potential as a unique disease control and plant protection strategy.

Successful biocontrol of major postharvest and soil-borne plant pathogenic fungi by antagonistic yeasts

Fungal pathogens are the main biotic burden of productivity for economically important crops under field, greenhouse or postharvest conditions. The discovery and development of new environmental-friendly solutions, such as application of living organisms and their derivatives to control plant diseases and pests, are of enormous interest. This study presents the results of a mass screening designed to detect yeast strains with antagonistic activity against postharvest pathogens (Alternaria alternata, Penicillium expansum and Botrytis cinerea) and soil-borne diseases (Verticillium dahliae and Fusarium oxysporum). In fact, this is the first study that focuses on screening the antagonistic potential of a wide variety of yeast genera (13) and species (30) against vascular wilts. The results from in vivo trials demonstrated that fungal infected tomato plants, grown under hydroponic or soil conditions, showed a significant reduction in disease severity after yeast treatment. Wickerhamomyces anomalus Wa-32 was able to antagonise both pathogens and reduce the disease severity up to 40% (V. dahliae) and 50% (F. oxysporum) in soil conditions. In addition, this strain became endophytic in tomato plants. The features of Wa-32 are of enormous interest since no effective antagonistic biocontrol product is available for the simultaneous control of these two fungal pathogens. Postharvest assays with wounded tomato fruits showed that several strains displayed very high biocontrol levels against P. expansum and B. cinerea (up to 86 and 97% reduction in disease severity, respectively) but none of them showed protection against A. alternata. The best protection against B. cinerea was again achieved with W. anomalus Wa-32 and two Metschnikowia pulcherrima strains (Mp-22 and Mp-30). However, the best antagonistic strains of P. expansum were Candida lusitaniae Cl-28, Candida oleophila Co-13, Debaryomyces hansenii Dh-67 and Hypopichia pseudoburtonii Hp-54. These biocontrol effects were also demonstrated in grapes and apples.

Synergistic Effects of a Tomato chlorosis virus and Tomato yellow leaf curl virus Mixed Infection on Host Tomato Plants and the Whitefly Vector.

In China, Tomato chlorosis virus (ToCV) and Tomato yellow leaf curl virus (TYLCV) are widely present in tomato plants. The epidemiology of these viruses is intimately associated with their vector, the whitefly (Bemisia tabaci MED). However, how a ToCV+TYLCV mixed infection affects viral acquisition by their vector remains unknown. In this study, we examined the growth parameters of tomato seedlings, including disease symptoms and the heights and weights of non-infected, singly infected and mixed infected tomato plants. Additionally, the spatio-temporal dynamics of the viruses in tomato plants, and the viral acquisition and transmission by B. tabaci MED, were determined. The results demonstrated that: (i) ToCV+TYLCV mixed infections induced tomato disease synergism, resulting in a high disease severity index and decreased stem heights and weights; (ii) as the disease progressed, TYLCV accumulated more in upper leaves of TYLCV-infected tomato plants than in lower leaves, whereas ToCV accumulated less in upper leaves of ToCV-infected tomato plants than in lower leaves; (iii) viral accumulation in ToCV+TYLCV mixed infected plants was greater than in singly infected plants; and (iv) B. tabaci MED appeared to have a greater TYLCV, but a lower ToCV, acquisition rate from mixed infected plants compared with singly infected plants. However, mixed infections did not affect transmission by whiteflies. Thus, ToCV+TYLCV mixed infections may induce synergistic disease effects in tomato plants.

Effectiveness of some biotic and abiotic agents to control tomato early blight disease caused by Alternaria solani

Bacillus megaterium, Bacillus subtilis, Pseudomonas fluorescens, Trichoderma harzianum, Trichoderma album and Trichoderma viride isolates, as well as different concentrations of chemical inducers, such as chitosan and salicylic acid were evaluated against Tomato early blight, under laboratory and greenhouse conditions. Under laboratory conditions, all tested bio agents, as well as the different concentrations of the tested chemical inducers, decreased the linear growth of A. solani, as the inhibition of fungal growth was increased by increasing the concentration of both chemical inducers in the growing medium. The chemical inducer chitosan at a concentration of 4.0 mg/mL PDA medium, caused the highest inhibition of linear growth of the fungus, followed by anti-fungus T. harzianum. When, different concentrations of chitosan and salicylic acid were tested on spore germination of A. solani, a concentration of 4.0 (mg/mL), for chitosan and a concentration of 25.0 (mM), for salicylic acid were the best concentrations used to reduce the spore germination of A. solani. Under greenhouse conditions, spraying tomato plants (cv. Super Strain B hybrid), with any of the tested biological agents as well as different concentrations of both the chemical inducers before infection of tomato plants by A. solani reduced the severity of early blight, in addition, to increase the fresh and dry weight of tomato plants. The chemical inducer chitosan at a concentration of 4.0 (mg/mL), caused the highest decrease of the disease severity, and the highest increase in fresh and dry weight of tomato plants, followed by the bio agent T. harzianum. The activities of defense-related enzymes i.e., polyphenoloxidase, peroxidase and chitinase were significantly increased in all treated plants with the tested biotic and abiotic agents. Chitosan at a concentration of 4.0 (mg/mL) resulted in the highest activity of oxidative enzymes, followed by T. harzianum. Meanwhile, the total content of phenols was higher in treated plants than in the untreated ones. The tested bio agents and chemical inducers might be playing an important role in management of tomato early blight through induction of induced systemic resistance.