Yellow Leaf Curl Virus Disease Research Articles

AmiRNA Technology Enhances Tomato Disease Resistance by Suppressing Plant-Pathogen Interaction Pathways through Inhibiting TYLCV Replication.

Tomato yellow leaf curl virus disease has seriously threatened the quality and yield of tomatoes. In this study, we investigated the role of amiRNA technology in disease resistance in tomatoes (cherry tomato and large-fruited tomato) and analyzed the physiological and molecular mechanisms of disease resistance in transgenic plants. TYLCV contains six functional genes, of which the C1, C2, and V1 genes have more phosphorylation sites and glycosylation sites, and the protein structure is more complex. The virus replication was inhibited, the peroxidation of membrane lipids was reduced, and disease resistance was enhanced in all transgenic cherry tomato (J6) plants in which the C1, C2, and V1 genes were silenced, respectively. Similarly, silencing of the C1 gene enhanced disease resistance in large-fruited tomatoes. In conclusion, amiRNA technology hinders viral replication, leading to reduced activity of the tomato plant-pathogen interaction pathway and weakening tomato-virus interactions, thereby improving disease resistance.

Evaluation of the Effect of Plant Age on Resistance to Tomato Yellow Leaf Curl Virus Disease and Age Relationship in Plants

The variables involved in ARR (Age - Related Resistance) to TYLCV in tomato plants were investigated in order to ascertain the impact of plant age and its link to disease development on gene expression of genetic resistance to TYLCV. Before being moved to the greenhouse, eleven virus-resistant and -susceptible kinds were nurtured in sterile conditions in Baghdad governorate’s protected nurseries. They were 15 days old when they went into the greenhouse to be planted on September 15, 2021. The virus-transmitting Bemisia tabaci bug was released into the plastic greenhouse following its activity, exposing the plants to direct infection. Afterwards, the plants were evaluated for their production, height, and molecular resistance by polymerase chain reaction (PCR). In addition, symptoms were tracked. All the cultivars evaluated showed a substantial decrease in yield when the plant was older when infected. Infection with TYLCV significantly reduced production for all cultivars. Our findings provide evidence that tomato plants develop resistance to TYLCV as they mature.

Ecoepidemiological Model and Optimal Control Analysis of Tomato Yellow Leaf Curl Virus Disease in Tomato Plant

The purpose of this study is to analyze the impact of control strategies, namely, insecticide spray, roguing of a diseased tomato plant, and protective netting to protect tomato plant from tomato yellow leaf curl virus disease (TYLCVD). For this, we formulate and analyze a simple deterministic model for the transmission dynamics of TYLCVD that incorporates these control strategies. We initially take into account the constant control case, we calculate the basic reproduction number, and we investigate the existence and stability of the disease-free and endemic equilibria. We use the Kamgang-Sallet stability to ensure that the disease-free equilibrium point is globally asymptotically stable when the reproduction number R 0 is less than one. This indicates that TYLCVD dies out independent of the initial size of the tomato population. For R 0 < 1 , the disease-free equilibrium becomes unstable, and the endemic equilibrium is globally asymptotically stable. This indicates that TYLCVD propagates. In the nonconstant control case, we use Pontryagin’s maximum principle to derive the necessary conditions for the optimal control of the disease. Our findings show that all the combined efforts of two out of three strategies can significantly reduce the power of infectivity of the disease except the combination of the use of insecticide spray and rouging infected tomato plants. Besides our numerical simulations show, the implementation of the combination of roguing diseased plants and protective netting has a similar effect in minimizing or eliminating TYLCV as the use of all strategies. Hence, as resources are always in scarce, we recommend policymakers to adapt the combination of the use of roguing diseased tomato plants and protective netting to eradicate the disease.

Response of Physicochemical Properties and Enzyme Activities in Rhizosphere Soil to Yellow Leaf Curl Virus Disease of Cherry Tomato (<i>Lycopersicon esulentum </i>Mill.)

Tomato yellow leaf curl virus disease (TYLCVD) has become a devastating disease, which seriously threatens the healthy development of tomato industry in China. Creating a healthy soil environment may be the key to success in preventing TYLCVD. Field investigation and laboratory analysis were used to evaluate the response characteristics of macro elements, medium elements, micro elements and enzyme activities in the rhizosphere soil of cherry tomato to TYLCVD. The main objective of this study was to determine the suitable soil environment for the healthy survival of cherry tomato. Soil samples were collected from rhizosphere of healthy and diseased plants. The results showed that the occurrence of TYLCVD was related to the enzyme activities, pH value, macro elements N, P, K, medium elements Ca, Mg, S and micro elements Mn, Zn, Cu, Si in the rhizosphere soil of cherry tomato. Compared with healthy plants, the activities of urease, catalase and acid phosphatase were significantly decreased by 48.6%–77.4%, 23.7%–43.8% and 19.1%–31.0%, respectively, in rhizosphere soil of diseased cherry tomato plants (<I>P</I> < 0.05). The pH value, contents of alkaline hydrolysis N, available Mg, available S, available Mn, available Zn, available Cu and available Si in rhizosphere soil of diseased plants were significantly lower than those in healthy plants (<I>P</I> < 0.05). The pH value in rhizosphere soil of diseased plants was 0.18-0.25 units lower than that of healthy plants. And the contents of alkaline hydrolysis N, available Mg, available S, available Mn, available Zn, available Cu and available Si were reduced by 5.54%–20.0%, 29.7%–73.9%, 27.3%–48.8%, 6.95%–10.1%, 13.6%–-15.2%, 10.6%–25.0% and 4.97%-8.30%, respectively. However, the contents of available P, available K and available Ca in rhizosphere soil of diseased plants were significantly higher than those in healthy plants (<I>P</I> < 0.05), were increased by 3.77%–41.2%, 6.75%–37.4% and 16.7%–50.5%, respectively. Our findings improve our understanding of the links between the occurrence of TYLCVD and the soil environment, which have implications for developing strategies for the prevention of tomato yellow leaf curl virus disease.

Transfer Learning based Image Classification of Diseased Tomato Leaves with Optimal Fine-Tuning combined with Heat Map Visualization

India is one of the leading countries in Tomato cultivation and production. Coimbatore, Dharmapuri, Salem,Krishnagiri are some of the foremost districts in tomato production. According to a survey, Tomato Leaf Curl virus is one of the most ravage class of disease and the maximum incidence of the disease is reported as 95.3% in Dharmapuri district of Tamil Nadu. The objective of the work is to identify the most recurrent tomato plant diseases using deep learning-based image classification techniques and to develop a plant disease classification web application. In this paper, Tomato based leaf disease images alone is used from Plant Village Dataset downloaded from Kaggle platform. Inception V3, a pre-trained transfer learning model is used to classify this multi-class tomato plant disease by using the leaf symptoms such as dark brown lesions, concentric rings etc. Data augmentation is performed while training the model on the images using Keras Image Data Generator on various layers and feature extraction is performed. The training accuracy and validation accuracy of the model before and after fine-tuning is 80.21%,76.29% and 81.72%,77.63% respectively. The highest precision, recall and F1 score is 95, 93 and 94 respectively is recorded for Tomato Yellow Leaf Curl Virus Disease for which the yield losses is severe. Further, activations are used to generate an attention map in the form of Heat Maps which is included as a post processing step before the classification of the output. Plant Leaf Disease Classification- A web application is deployed using Streamlit Python library and Ngrok services

Management of Tomato Yellow Leaf Curl Virus (TYLCV) Infecting Tomato by using Calcium Rich Compounds

Bemisia tabaci (whitefly) transferred Tomato yellow leaf curl virus (TYLCV) disease is a significant constraint on tomato productivity. One technique for managing the condition is to spray calcium compounds (calcium carbonate, calcium chloride, calcium nitrate) onto tomatoes. According to the research findings, the incidence of TYLCV was lower in calcium compound sprayed plants than in control plants. The control group had the greatest TYLCV prevalence. Calcium carbonate-treated plants had the lowest TYLCV, followed by calcium nitrate-treated plants. Temperature and relative humidity were shown to be strongly linked with the population of whiteflies, the TYLCV vector in the tomato field. The expansion of TYLCV in tomatoes and the growth in whitefly populations were shown to have positive and substantial connections. In terms of plant height, fresh shoot weight, dried shoot weight, and root length, the three calcium compounds outperformed the others. Furthermore, the number of fruit/plants in the calcium carbonate spray was shown to be higher than in the control. With a few exceptions, calcium carbonate and calcium nitrate treatments were shown to be superior to calcium chloride treatments in terms of increasing growth and yield, contributing to character as well as yield.

Relationship between some morphological traits of the tomato lines and resistance to tomato yellow leaf curl virus disease

Tomato (Solanum lycopersicum L.) is the most produced and exported vegetable in Turkey. There are many pathogens to limit tomato production by reducing yield and fruit quality. Among them, Tomato Yellow Leaf Curl Virus (TYLCV) causes important economic losses. The most efficient and environmentally friendly method against TYLCV is the use of resistant varieties. In this trial, it was aimed to determine some morphological traits which were linked to Ty-1 and Ty-3a genes which confer to TYLCV. A commercial hybrid carrying Ty-1, Ty-3a genes as heterozygous was crossed to a susceptible inbred line from Bati Akdeniz Agricultural and Research Institute (BATEM). Marker assisted selection (MAS) was carried out in F1 and F2 generations and biological tests were done for TYLCV resistance in F3 generation. MAS for Ty-3a and Ty-1 genes were compatible with biological tests. In total of 95 genotypes in F3 were developed with molecular marker selection. It was determined that 30 genotypes having the Ty-3a and Ty-1 genes as homozygous resistant. The nine genotypes carried these genes in heterozygous form. 56 genotypes were identified as susceptible. The 43 morphological traits were observed in identified individuals to correlate with resistant allele, Ty-3a. It was found that there was statistically important correlation between Ty-3a and length of internode, length of stem at first inflorescence, status of calix, leaf attitude, length of inflorescence and plant habitus. Also, there was negative correlation between fruit weight, fruit length and resistance. Therefore, we identified some morphological markers linked to Ty-3a which can be used in selection for TLYCV resistant breeding programme.

Integrated Management of Tomato Yellow Leaf Curl Virus and its Whitefly Vector in Tomato.

Whitefly-transmitted Tomato yellow leaf curl virus (Family Geminiviridae; Genus Begomovirus) severely restricts tomato production in the Southeastern United States. Whitefly and tomato yellow leaf curl virus management studies typically investigate control tactics individually, but successful management of this pest complex more often relies on a combination of tactics. This study examined the individual and combined effects of tomato yellow leaf curl virus-resistant cultivars, insecticides, and metallic reflective mulch on whiteflies, tomato yellow leaf curl virus disease incidence, and marketable tomato yields using split-split plot trials over 3 yr. Reflective mulch significantly reduced whitefly adults and nymphs and tomato yellow leaf curl virus symptom severity in all 3 yr of the study. Reflective mulch treatments also provided greater marketable tomato yield in 2 out of 3 yr. Imidacloprid and cyantraniliprole treatments reduced whitefly adults and nymphs' establishment and marginally increased yields, but there was no significant insecticide effect on tomato yellow leaf curl virus incidence/symptom severity compared with the non-treated check. Virus-resistant tomato cultivars did not influence whitefly populations, but provided consistent reduction in virus disease incidence. Interactions between host plant resistance and insecticide treatments ranged from strongly additive in the standard white plastic mulch treatment to only marginally additive in the reflective mulch treatments in terms of enhancing tomato yields. tomato yellow leaf curl virus-resistant tomato cultivars and reflective mulch provided the bulk of the protection against tomato yellow leaf curl virus disease incidence. However, it was the combination of all the best tactics (reflective mulch, cyantraniliprole, 'Security' hyb. tomato yellow leaf curl virus-resistant) that provided the maximum increase in marketable tomato yield (2.8-fold) over the least effective combination (white mulch, no whitefly insecticide, 'FL47' hyb. tomato yellow leaf curl virus-susceptible).

Bacillus amyloliquefaciens Ba13 induces plant systemic resistance and improves rhizosphere microecology against tomato yellow leaf curl virus disease

The control effect of Bacillus against tomato yellow leaf curl virus (TYLCV) disease has not been reported. It is not clear whether adjustment of the rhizosphere microbial community structure by beneficial microbes applied as biocontrol agents is related to their role in increasing resistance of plants to viral diseases. Therefore, the objective of this study was to investigate the control effect and mechanism of Bacillus amyloliquefaciens Ba13 against TYLCV disease. Two treatments including control and Ba13 treatment followed by natural infection with whiteflies were conducted. We measured plant growth, physiological parameters, disease severity, and leaf virus quantity and also assayed resistance-related gene expression, defense enzyme activity, and rhizosphere microbial community structure. Strain Ba13 lowered the infection rate, disease severity, and leaf virus quantity in tomato plants, with the control rate of 48–52%. Root development and shoot biomass markedly improved in tomato following Ba13 treatment. Ba13 elevated expression of pathogenesis-related PR1, PR2, and PR3 genes, and enhanced activities of phenylalanine ammonia lyase, polyphenol oxidase, peroxidase, β-1,3 glucanase, and chitinase in tomato leaves. Cultivation-dependent microbiological analysis showed that Ba13 increased the bacteria-to-fungi ratio and the number of beneficial microbes while decreasing the number of pathogenic fungi in the rhizosphere. Further analysis revealed the potential of a dominant rhizosphere bacterium, B. velezensis B3, to promote plant growth and improve systemic resistance in tomato. B. amyloliquefaciens Ba13 can enhance plant resistance against TYLCV disease through direct induction of systemic resistance and also by increasing the number of beneficial microbes in the rhizosphere, thereby achieving control of TYLCV disease.

Streptomyces pactum Act12 controls tomato yellow leaf curl virus disease and alters rhizosphere microbial communities

Actinomycetes comprise a large group of biocontrol bacteria, yet no studies have reported on their effects against plant virus diseases. Here, we evaluated the control effects and the possible mechanisms of Streptomyces pactum Act12 against tomato yellow leaf curl virus disease (TYLCD) through field and pot experiments. We also analyzed changes in plant growth and rhizosphere microbial community composition following the application of Act12. The pre-inoculation of soil with the Act12 agent enhanced the activities of peroxidase and chitinase while upregulating the expression of genes related to plant systemic resistance (PR-1 and SIPI-II) and specific TYLCD resistance (SIPer1 and SIVRSLip) in tomato leaves under field conditions. The effects of Act12 at inducing a decline in TYLCD severity and promoting plant growth were deemed satisfactory in all three field experiments. In the pot experiments, Act12 induced a decline in the viral DNA level and an enhancing of peroxidase, polyphenoloxidase, and phenylalanine ammonia lyase activities in tomato leaves. Additionally, Act12 treatment reduced the accumulation of H2O2 and O·−2, increased the levels of salicylic and jasmonic acids, and upregulated the expression of genes related to plant resistance and RNA interference in tomato leaves. Applying Act12 also increased the diversity of bacteria and the abundance of potential beneficial microbes (e.g., Trichoderma and Bacillus) in the root-zone and root-surface soils, resulting in modular differentiation of co-occurrence networks. In conclusion, applying the S. pactum Act12 agent reduced TYLCD severity and promoted plant growth in tomato. Whether the changes of resistance-related gene expression and rhizosphere microbial community composition contribute to TYLCV resistance needs to be further investigated.

Farmers Agronomic Practice in Management of the Tomato (&lt;i&gt;Solanum lycopersicon&lt;/i&gt; L.) Yellow Leaf Curl Virus in Central Region of Ghana

The study assessed farmers’ awareness of the Tomato yellow leaf curl virus (TYLCV) disease and their agronomic and disease management practices in the Efutu municipality, Komenda-Edina-Eguafo-Abirem (KEEA), and Mfantseman districts which are leading tomato producing centres in the Central Region of Ghana. The study also surveyed the incidence and severity of the TYLCV disease in tomato fields across the three districts. Household data were collected using structured questionnaire from 150 respondents using multi-stage procedure, and analysed using descriptive statistics. Incidence (DI) and severity index (SI) of TYLCV disease were determined from forty (40) tomato fields selected from each of the three districts. The field data was subjected to analysis of variance (ANOVA) and the means separated with least significant difference (l.s.d) method at 5% level of probability.Majority of the farmers (92.6%) were aware of the TYLCVdisease and said it could cause yield losses rangingfrom less than 10% to over 41% but did not know the cause.Majority (60.4%) of the farmers managed the TYLCV disease in their farms mainly by applying insecticides (55.6%) and roguing of diseased plants (43.1%). About 60.7% of the farmers practiced mixed cropping, and most of them cultivated tomato in both the major and minor cropping seasons, using mainly an improved form of Solanum pimpinellifolium . The highest mean disease incidence and mean disease severity indices were recorded at KEEA (52.9±2.7%, 26.89±1.2%), followed by Efutu (49.5±1.19%, 25.29±0.9%), and Mfantseman (42.1±2.7%, 21.41±0.8%) respectively.In conclusion, TYLCV was highly prevalent in the study area, but infection was moderate due to the use of improved tomato variety.

Suppressive effect of acetylated glyceride (Bemidetach™EC) on Tomato yellow leaf curl virus transmitted by the whitefly Bemisia tabaci on greenhouse tomato plants

Acetylated glyceride (Bemidetach™EC)—a food additive—repels adult sweet potato whiteflies (Bemisia tabaci) and inhibits their mating behavior. We evaluated the effects of acetylated glyceride spraying of greenhouse-grown tomato plants on infestation with B. tabaci and the occurrence of Tomato yellow leaf curl virus (TYLCV) disease under commercial-like conditions. The abundance of adult B. tabaci was significantly reduced by three sprayings of acetylated glyceride, and the TYLCV incidence was significantly suppressed to less than 30% of that in the untreated control. These results suggest that acetylated glyceride sprays suppress the secondary spread of TYLCV in greenhouse-grown tomatoes by lessening B. tabaci adult density.

Control of Tomato yellow leaf curl virus disease by Enterobacter asburiaeBQ9 as a result of priming plant resistance in tomatoes

Enterobacter asburiae BQ9, a plant-growth-promoting rhizobacterium, was shown to promote tomato plant growth and induce resistance to Tomato yellow leaf curl virus (TYLCV) under greenhouse conditions. Compared with mock-treated tomato plants, plants that were pretreated with BQ9 had increased fresh mass and significantly reduced disease severity and 52% biocontrol efficacy was achieved 30 days after inoculation. The expression of defense-related genes PR1a and PR1b and the H 2 O 2 burst were quickly induced in BQ9 pretreated plants. Antioxidase activity analysis showed that the activities of phenylalanine ammonia lyase, peroxidase, catalase, and superoxide dismutase increased significantly in BQ9 pretreated plants. Our results suggest that the plant-growth-promoting rhizobacterium BQ9 induced a priming of the plant defense responses to TYLCV by increasing the expression of defense response genes, and the induced resistance was mechanistically connected to the expression of antioxidant enzymes and the production of H 2 O 2 .

재배작형에 따른 토마토황화잎말림바이러스병의 발병양상

전남지역의 영암, 장성, 화순 등 주요 재배주산지에서 2012년부터 2013년까지 2년동안 토마토황화잎말림바이러스 병의 발생현황을 조사하였다. 바이러스는 토마토 시료로부터 전체 DNA를 추출하여 PCR을 실시하였다. 토마토 재배작형별 바이러스 발병포장율은 반촉성작형은 23%, 억제작형은 59.4%였으며, 이병주율은 각각 0.4%, 13.1%였다. 저항성품종 재배시에는 작형에 관계없이 발병율이 매우 낮았으며, 감수성 품종 재배시에는 발병포장율은 반촉성은 24.3%로 낮았으나, 억제작형은 83.0%로 매우 높았다. 하지만 저항성 품종 재배시에는 발병 포장율은 반촉성은 발생되지 않았고, 억제작형은 9.1%였다. 토마토황화잎말림바이러스는 4월 정식시 6월 상순부터 발생하였고, 8월과 9월에 정식하였을 때 20일 후부터 발생하기 시작하였다. Tomato yellow leaf curl virus (TYLCV) disease survey of tomato plants cultivated at Youngam, Changseong and Hwasun in Jeonnam Province was conducted in 2012 to 2013. To detect TYLCV in the field, PCR assay was performed using genomic DNAs extracted from tomato samples. According to cropping pattern, 23 and 59.4% of TYLCV infections were shown in semi-forcing and retarding cropping systems, respectively, and the frequencies of diseased plants were 0.4 and and 13.1% in the two cropping systems, respectively. Especially, TYLCV incidences in the susceptible varieties were 24.3 and 83.0% in semi-forcing and retarding cropping systems, respectively. Resistant varieties showed 9.1% infection in retarding cropping system but did not in semi-forcing cropping system. Also, TYLCV was occurred on early June after transplanting on April and at approximate 20 days after transplanting on August or September.

Tomato yellow leaf curl virus resistance by Ty-1 involves increased cytosine methylation of viral genomes and is compromised by cucumber mosaic virus infection.

Tomato yellow leaf curl virus (TYLCV) and related begomoviruses are a major threat to tomato production worldwide and, to protect against these viruses, resistance genes from different wild tomato species are introgressed. Recently, the Ty-1 resistance gene was identified, shown to code for an RNA-dependent RNA polymerase and to be allelic with Ty-3. Here we show that upon TYLCV challenging of resistant lines carrying Ty-1 or Ty-3, low virus titers were detected concomitant with the production of relatively high levels of siRNAs whereas, in contrast, susceptible tomato Moneymaker (MM) revealed higher virus titers but lower amounts of siRNAs. Comparative analysis of the spatial genomic siRNA distribution showed a consistent and subtle enrichment for siRNAs derived from the V1 and C3 genes in Ty-1 and Ty-3. In plants containing Ty-2 resistance the virus was hardly detectable, but the siRNA profile resembled the one observed in TYLCV-challenged susceptible tomato (MM). Furthermore, a relative hypermethylation of the TYLCV V1 promoter region was observed in genomic DNA collected from Ty-1 compared with that from (MM). The resistance conferred by Ty-1 was also effective against the bipartite tomato severe rugose begomovirus, where a similar genome hypermethylation of the V1 promoter region was discerned. However, a mixed infection of TYLCV with cucumber mosaic virus compromised the resistance. The results indicate that Ty-1 confers resistance to geminiviruses by increasing cytosine methylation of viral genomes, suggestive of enhanced transcriptional gene silencing. The mechanism of resistance and its durability toward geminiviruses under natural field conditions is discussed.

FIRST REPORT OF SOLANUM ELAEAGNIFOLIUM AS NATURAL HOST OF TOMATO YELLOW LEAF CURL VIRUS SPECIES (TYLCV AND TYLCSV) IN TUNISIA

Tomato yellow leaf curl virus (TYLCV) and Tomato yellow leaf curl Sardinia virus (TYLCSV) (genus Begomovirus, family Geminiviridae), as well as recombinant variants, were recently found in tomato in Tunisia (Mnari-Hattab et al., 2014). To identify sources of infection, tomato plants and Solanum elaeagnifolium, an invasive weed, were sampled and tested for the presence of TYLCV and TYLCSV. Genomic DNA was purified from leaf samples showing curling and yellowing and subjected to PCR using primers designed in the coat protein gene of TYLCV (Mnari-Hattab et al., 2014; Wyatt and Brown, 1996). A product of ca. 580 bp was obtained from four of six S. elaeagnifolium and six of six tomato samples tested. The nucleotide sequence of one amplicon from tomato and two amplicons from S. elaeagnifolium was obtained and deposited in GenBank as accession numbers KF990598, KF990599 and KF990600. The nucleotide sequence of Tunisian TYLCV isolates was 91.2 to 98.9% identical and shared 91 to 98.3% identity with a TYLCV isolate from Turkey (AJ867487). Multiplex PCR (Davino et al., 2008) was further used to identify virus species with the amplification of a 570 bp fragment for TYLCV and a 800 bp fragment for TYLCSV. Results showed two S. elaeagnifolium and four tomato plants infected with TYLCV or TYLCSV, and two S. elaeagnifolium and one tomato plant infected with both viruses. To the best of our knowledge, this is the first report of S. elaeagnifolium as a natural host of TYLCV and/or TYLCSV in Tunisia. These findings suggest S. elaeagnifolium as a reservoir for tomato yellow leaf curl virus disease.

Natural occurrence of begomovirus recombinants associated with tomato yellow leaf curl disease co-existing with parental viruses in tomato crops and weeds in Tunisia

Tomato yellow leaf curl virus disease (TYLCVD) is the main limiting factor for tomato production in the Mediterranean Basin, and particularly in Tunisia where climatic and crop production conditions, as well as the occurrence of many weeds, provide suitable conditions for the presence and spread of TYLCVD all year round. In Tunisia, epidemics in tomato-growing regions have been associated with two begomoviruses: Tomato yellow leaf curl virus (TYLCV) and Tomato yellow leaf curl Sardinia virus (TYLCSV) but the presence of recombinants between them has never been investigated. A large-scale survey was conducted on leaves sampled from late-season tomato crops exhibiting severe curling symptoms, from beans, and from nine nearby weed species in the South and Sahel regions of Tunisia to investigate: (i) the natural occurrence of the TYLCV and TYLCSV species; (ii) the presence of the two recombinant types, RecA and RecB, derived from these species. Identification of TYLCV and TYLCSV was based on a multiplex PCR with primers generating a typical pattern on gels (750 bp and 366 bp fragments, respectively). Recombinants were identified by simplex PCR, which amplified the intergenic region, the most common recombination site described for begomoviruses, and sequencing. The occurrence of TYLCSV and TYLCV was confirmed in both Tunisian regions. Their co- existence was shown on tomato and in new weed species. This is the first time that recombinants between TYLCV and TYLCSV species showing 93% to 95% nucleotide identity with tomato yellow leaf curl recombinant viruses, are reported in Tunisia in tomato and black nightshade.

Eugenol enhances the resistance of tomato against tomato yellow leaf curl virus

Tomato yellow leaf curl virus disease (TYLCVD) causes severe to economic losses in tomato crops in China. The control of TYLCVD is based primarily on the use of synthetic insecticide to control its vector whitefly (Bemisia tabaci). To look for an alternative method for disease control, we investigated the effect of eugenol on controlling TYLCVD. The potential of eugenol to trigger systemic acquired resistance (SAR) in tomato (Jiangsu 14) plants against TYLCV was also investigated. In greenhouse experiments, eugenol significantly reduced disease severity when applied as a foliar spray, thus demonstrating a systemic effect. The disease spread rapidly in control plants and by the end of the experiment almost all control plants showed severe symptoms. Eugenol also induced H₂O₂ accumulation in tomato plants. Activities of peroxidase (POD), polyphenol oxidase (PPO) and phenylalanine ammonia lyase (PAL) were significantly induced compared with those of control plants. As further consequences, increase of salicylic acid (SA) levels and expression of PR-1 proteins, a molecular marker of SAR in tomato, could also be observed. This is the first report of eugenol as an elicitor and its ability to suppress plant virus diseases under greenhouse conditions. It is suggested that eugenol has the potential to be an effective biocontrol agent against TYLCV in tomato plants.

The Tomato Yellow Leaf Curl Virus resistance genes Ty-1 and Ty-3 are allelic and code for DFDGD-class RNA-dependent RNA polymerases.

Tomato Yellow Leaf Curl Virus Disease incited by Tomato yellow leaf curl virus (TYLCV) causes huge losses in tomato production worldwide and is caused by different related begomovirus species. Breeding for TYLCV resistance has been based on the introgression of multiple resistance genes originating from several wild tomato species. In this study we have fine-mapped the widely used Solanum chilense–derived Ty-1 and Ty-3 genes by screening nearly 12,000 plants for recombination events and generating recombinant inbred lines. Multiple molecular markers were developed and used in combination with disease tests to fine-map the genes to a small genomic region (approximately 70 kb). Using a Tobacco Rattle Virus–Virus Induced Gene Silencing approach, the resistance gene was identified. It is shown that Ty-1 and Ty-3 are allelic and that they code for a RNA–dependent RNA polymerase (RDR) belonging to the RDRγ type, which has an atypical DFDGD motif in the catalytic domain. In contrast to the RDRα type, characterized by a catalytic DLDGD motif, no clear function has yet been described for the RDRγ type, and thus the Ty-1/Ty-3 gene unveils a completely new class of resistance gene. Although speculative, the resistance mechanism of Ty-1/Ty-3 and its specificity towards TYLCV are discussed in light of the function of the related RDRα class in the amplification of the RNAi response in plants and transcriptional silencing of geminiviruses in plants.

Participatory Evaluation of Tomato Varieties for Commercial Cultivation During Rainy Season Under Kaymore Plateau and Satpura Hills – Agro-Climatic Zone of Madhya Pradesh

Four tomato varieties, namely Kashi Vishesh, Kashi Anupam, Kashi Amrit and Hisar Arun (S-7), were evaluated against the variety Navoday in farmer's field with farmer’s participation for yield potential and other yield characters at Satna, Madhya Pradesh during rainy seasons of two consecutive years 2009 and 2010. The experiment was arranged in complete randomized block design with 5 replications, farmer as a replication. The results of the experiment revealed that all the tested varieties have more yield potentiality than Navoday variety. Kashi Vishesh took the least time to flowering (44.49 days) and first harvest (73.14 days) after transplanting, gave the highest survivability of plants at harvest (91.25%), produced the maximum number of clusters per plant (11.90), number of flowers per cluster (1.99), number of fruits per plant (23.02), the highest marketable fruit yield (290.29 q per ha) and had the low incidence of Yellow Leaf Curl Virus disease. The investigation led to infer that Kashi Vishesh was the best-performing variety, and therefore, it could be recommended for commercial production during rainy season under rain fed conditions in well drained soils of the undulating terrain. Kashi Anupam with moderate high yield and some tolerance to Tomato Yellow Leaf Curl Virus might be regarded as other potential variety for the rainy season production of tomato.