The Economic Impact and Integrated Management Strategies against Tomato Yellow Leaf Curl Virus (TYLCV): A Review

Tomato yellow leaf curl disease (TYLCD) and tomato leaf curl disease (TLCD) cause serious losses in tomato production, especially in tropical and sub-tropical regions. In 2014–2015, tomato samples with TYLCD/TLCD-like symptoms were collected from different provinces of Iraq and infection with tomato yellow leaf curl virus (TYLCV) identified. To study the diversity of TYLCV, DNA of eight positive samples from this survey was used for rolling-circle amplification, cloning and sequencing. Pairwise nucleotide sequence comparisons with complete genomes showed that the Iraqi TYLCV isolates belonged to the strains TYLCV-IL and TYLCV-Mld. In a phylogenetic analysis, the Iraqi TYLCV-IL isolates grouped into three distinct clades, consisting of TYLCV-IL (A) and the two new variants TYLCV-IL (D) and TYLCV-IL (E). The Iraqi isolate of TYLCV-Mld grouped into the newly proposed TYLCV-Mld (D) variant. For one sample, sequencing also revealed co-infection with tomato leaf curl Palampur virus (ToLCPalV). The phylogenetic tree of ToLCPalV DNA-A showed a close relationship between the isolates of different hosts from Iraq and Iran. No evidence of recombination was detected in ToLCPalV DNA-A, but recombination was observed for the TYLCV isolates. The results indicate that there is a high diversity of TYLCV in Iraq, including new variants, that is partly shared with Kuwait and countries in the Eastern Mediterranean Region. Occurrence of multiple TYLCV variants and ToLCPalV can act as a potential threat to tomato production in Iraq.

국내에서 채집한 5종의 토마토황화잎말림바이러스(Tomato yellow leaf curl virus, TYLCV) 분리주들에 대하여 PCR법을 이용하여 염기서열을 결정하였다. 전체 유전체의 1.9배 복제수를 가지는 감염성 클론을 제작하기 위하여, PCR로 증폭된 TYLCV DNA를 식물형질전환용 벡터에 각각 도입시켰다. TYLCV 저항성 평가를 위하여 저항성 토마토 시판 품종과 육성 계통을 각각 TYLCV 분리주를 가지고 있는 Agrobacterium tumefaciens로 접종하였다. 감수성 품종인 'Super-sunroad' 품종은 접종 30일 후에 상엽에 황화, 위축 증상을 나타낸 반면, TYLCV에 대한 저항성유전자들로 알려진 Ty-1 또는 Ty-3 유전자를 포함하고 있는 TY12, GC9, GC171, GC173 등의 토마토 육성 계통은 전신 잎에 TYLCV 병징 발현이 없었으므로 이들 계통은 TYLCV 저항성으로 판별되었다. Agroinfiltration을 통한 접종 30일에 감수성 품종과 저항성 품종 간에 TYLCV 병징 차이가 뚜렷하였다. 특이적 프라이머들을 이용한 실시간 PCR법에 의해 TY12, GC9, GC171, GC173 육성 계통에서 TYLCV DNA가 검출되었지만, 저항성 계통에서 TYLCV DNA 축적 수준은 감수성 토마토 품종에서의 TYLCV DNA 축적 수준보다 매우 낮았다. 유사한 병징 세기 및 TYLCV DNA 축적 수준이 담배가루이를 통하여 감수성과 저항성 토마토 품종 및 육성 계통에 TYLCV를 감염시켰을 때에도 관찰되었다. Agroinfiltration 시 아그로박테리움의 농도는 토마토 품종의 TYLCV 저항성 반응에 영향을 미치지 않았다. 따라서 본 연구결과들은 agroinfiltration을 통한 TYLCV 접종이 담배가루이를 통한 TYLCV 감염처럼 효과적이며 TYLCV 저항성 토마토 육성 프로그램에 활용 가능하다는 것으로 보여주었다. Five isolates of Tomato yellow leaf curl virus (TYLCV) collected from various regions of Korea were amplified using PCR and determined the sequences of full-length genome, respectively. The PCR-amplified DNA of each TYLCV isolate was introduced into a binary vector to construct infectious clone containing 1.9 copies of the corresponding viral genome. Various cultivars and breeding lines of tomato were inoculated with Agrobacterium tumefaciens harboring infectious clone of each TYLCV isolate to assess resistance against TYLCV. Susceptible cultivar 'Super-sunread' revealed typical yellowing and narrowing of the upper leaves. In contrast, breeding linesTY12, GC9, GC171, and GC173, which contained the TY-1 and/or TY-3 genes that confer resistance against TYLCV in nature, were completely symptomless, suggesting that the lines were resistant to challenging TYLCV isolates. Symptoms of TYLCV in susceptible tomato cultivars are significantly different from those of TYLCV in the resistant tomato cultivars at 30 days after agroinfiltration. Although genomic DNAs of TYLCV were detected from the breeding lines TY12, GC9, GC171, and GC173 using real-time PCR analysis with specific primers, levels of TYLCV DNA accumulation in the resistant breeding lines were much lower than those of TYLCV DNA accumulation in susceptible tomato cultivars. Similar symptom severity and levels of TYLCV DNA accumulation were observed from TYLCV infections mediated by Bemisia tabaci in the resistant and susceptible tomato cultivars. Concentration of agrobacterium did not affect the response of tomato cultivars against TYLCV inoculation. Taken together, these results suggest that TYLCV inoculation via agroinfiltration is as effective as inoculation through Bemisia tabaci and is useful for breeding programs of TYLCV-resistant tomato.

Begomoviruses, which constitute one genus of the Geminiviridae family, are single-stranded DNA viruses that infect many dicotyledonous crops important to large agricultural industries as well as to subsistence growers. Although all begomoviruses are transmitted by whiteflies (Bemisia tabaci), they have proven difficult to manage even with heavy insecticide applications. The begomovirus, Tomato yellow leaf curl virus (TYLCV), has been a problem in tomato production in Israel since the 1950s and in the United States since 1997. Approximately 89 begomoviruses have now been reported to infect tomato. Crop losses due to begomoviruses such as TYLCV and Tomato mottle virus (ToMoV), are limiting factors in tomato cultivation in Israel, the U.S., and many tomato-growing regions throughout the world. To overcome these limitations, we proposed a two-step strategy that combines transgenic and conventional resistance in order to develop tomato plants that are resistant to multiple begomoviruses. In the first step, we have developed transgenic tomato plants expressing trans-dominant interfering mutants Rep and C3 from TYLCV and ToMoV, and tested whether these plants are resistant to infection by these two viruses. In the second step we have tested whether pyramiding transgenic and conventional resistance is superior to either strategy alone. The specific objectives of the proposal were: 1. Design and test trans-dominant interfering constructs for TYLCV and ToMoV Rep and C3 in transient replication interference assays. 2. Generate and test transgenic tomato plants expressing mutant Rep and C3 in resistance assays. 3. Generate and test conventional resistant lines that also express mutant Rep and C3. Two viral replication interfering constructs, expressing the trans-dominant interfering mutants Rep and C3, were designed and constructed during this project. One construct, pNSB1630 was based on TYLCV sequences and the other, pNSB1682, based on ToMoV sequences. The TYLCV transformation construct was tested in a protoplasts replication assay, and was found to inhibit TYLCV replication. The ToMoV transformation construct is yet to be tested in a protoplast assay. Both transformation vectors, pNSB1630 and pNSB1682, were used to transform four different tomato lines, and generate transgenic plants. The tomato lines used for transformation were: FL7613, MM, TY172, TY199. FL7613 and MM are susceptible to both TYLCV and ToMoV. TY172 and TY199 are breeding lines developed at Volcani Center. TY172 is resistant to TYLCV but susceptible to ToMoV, while TY199 is resistant to both TYLCV and ToMoV. When transgenic T1 plants expressing the pNSB1630 constructed were screened for TYLCV resistance, it was found that these plants showed very low level of TYLCV resistance, if any. However, some of these lines showed high level of resistance to ToMoV. Only five transgenic T1 lines expressing the pNSB1682 construct were tested (so far) for resistance to ToMoV. It was found that all five lines express very high level of resistance to ToMoV. Although we haven’t finished (yet) the screen of all the transgenic lines, it is already clear that we were able to successfully combine genetic resistance for TYLCV with transgenic resistance to ToMoV.

Establish an efficient inoculation system of tomato yellow leaf curl virus to assist tomato resistance breeding

Tomato yellow leaf curl virus (TYLCV) and Tomato spotted wilt virus (TSWV) are prevalent in field-grown tomato (Solanum lycopersicum) production in Georgia. Typical TYLCV symptoms were observed during varietal trials in fall 2009 and 2010 to screen genotypes against TYLCV at the Coastal Plain Experiment Station, Tifton, GA. However, foliar symptoms atypical of TYLCV including interveinal chlorosis, purpling, brittleness, and mottling on upper and middle leaves and bronzing and intense interveinal chlorosis on lower leaves were also observed. Heavy whitefly (Bemisia tabaci (Gennadius), B biotype) infestation was also observed on all tomato genotypes. Preliminary tests (PCR and nucleic acid hybridization) in fall 2009 indicated the presence of TYLCV, TSWV, Cucumber mosaic virus, and Tomato chlorosis virus (ToCV); all with the exception of ToCV have been reported in Georgia. Sixteen additional symptomatic leaf samples were randomly collected in fall 2010 and the preliminary results from 2009 were used to guide testing. DNA and RNA were individually extracted using commercially available kits and used for PCR testing for ToCV, TYLCV, and TSWV. Reverse transcription (RT)-PCR with ToCV CP gene specific primers (4) produced approximately 750-bp amplicons from nine of the 16 leaf samples. Four of the nine CP gene amplicons were purified and directly sequenced in both directions. The sequences were 99.4 to 100.0% identical with each other (GenBank Accession Nos. HQ879840 to HQ879843). They were 99.3 to 99.5%, 97.2 to 97.5%, and 98.6 to 98.9% identical to ToCV CP sequences from Florida (Accession No. AY903448), Spain (Accession No. DQ136146), and Greece (Accession No. EU284744), respectively. The presence of ToCV was confirmed by amplifying a portion of the HSP70h gene using the primers HSP-1F and HSP-1R (1). RT-PCR produced approximately 900-bp amplicons in the same nine samples. Four HSP70h gene amplicons were purified and directly sequenced in both directions. The sequences were 99.4 to 99.7% identical to each other (Accession Nos. HQ879844 to HQ879847). They were 99.2 to 99.5%, 98.0 to 98.4%, and 98.9 to 99.3% identical to HSP70h sequences from Florida (Accession No. AY903448), Spain (Accession No. DQ136146), and Greece (Accession No. EU284744), respectively. TYLCV was also detected in all 16 samples by PCR using degenerate begomovirus primers PAL1v 1978 and PARIc 496 (3) followed by sequencing. TSWV was also detected in two of the ToCVinfected samples by RT-PCR with TSWV N gene specific primers (2) followed by sequencing. To our knowledge, this is the first report of the natural occurrence of ToCV in Georgia. Further studies are required to quantify the yield losses from ToCV alone and synergistic interactions between ToCV in combination with TSWV and/or TYLCV in tomato production in Georgia.

Tomato yellow leaf curl virus (TYLCV) is one of the most harmful afflictions in the world that affects tomato growth and production. Six regular antagonistic genes (Ty-1, Ty-2, Ty-3, Ty-4, ty-5, and Ty-6) have been transferred from wild germplasms to commercial cultivars as TYLCV protections. With Ty-1 serving as an appropriate source of TYLCV resistance, only Ty-1, Ty-2, and Ty-3 displayed substantial levels of opposition in a few strains. It has been possible to clone three TYLCV opposition genes (Ty-1/Ty-3, Ty-2, and ty-5) that target three antiviral safety mechanisms. However, it significantly impacts obtaining permanent resistance to TYLCV, trying to maintain opposition whenever possible, and spreading opposition globally. Utilizing novel methods, such as using resistance genes and identifying new resistance resources, protects against TYLCV in tomato production. To facilitate the breeders make an informed decision and testing methods for TYLCV blockage, this study highlights the portrayal of typical obstruction genes, common opposition sources, and subatomic indicators. The main goal is to provide a fictitious starting point for the identification and application of resistance genes as well as the maturation of tomato varieties that are TYLCV-resistant.

Egypt is facing a major problem in the field of tomato seed production, as infection with the yellow tomato leaf curl virus (TYLCV) is one of the most important factors in the success of this important production process, which has an impact on national food security, in addition to facing the steady increase in the costs of importing tomato seeds in particular vegetable crop seeds in general. Therefore, the main objective of the current study is to study plant age-related induced resistance (ARIR) against tomato yellow leaf curl virus (TYLCV) in tomato plants. Several research points were studied, respectively: first, the effect of plant age on resistance to TYLCV virus in tomato plants that is transmitted by whitefly. Second, the detection and identification of tomato yellow leaf curl virus (TYLCV) in seeds obtained from seedlings of different ages (35 and 90 days old). Third, study the behavior of the whitefly in terms of the number of eggs and larvae, the percentage of the number of infected plants that showed symptoms of infection with the virus, and its relationship to the age of the seedlings. The results of this study proved that the age of the plant is closely related to the ability of the plant to withstand infection with the tomato yellow leaf curl virus (TYLCV). The DNA of the tomato yellow leaf curl virus (TYLCV) was identified from a sample of seeds obtained from plants obtained from 35-day-old seedlings. On the contrary, the DNA of tomato yellow leaf curl virus (TYLCV) was not detected in the seed sample obtained from plants produced from 90-day-old seedlings that were cultivated and adapted inside the nursery. The results also showed that in both protocols, using or without insecticides did not prevent the white fly from laying eggs and producing larvae on the plants. The increase was also gradual in the numbers of eggs and larvae of the white fly, as this activity peaked in the third week of transferring the seedlings to the open field, then those numbers decreased after the third week. This study also demonstrated the effect of positive seedling age (90 days old) on morphological traits related to vegetative growth, fruit production, and seed yield. Among the important benefits obtained was the ability to obtain seeds free of TYLCV in tomato plants, as well as the ability to remove nursery plants that showed early symptoms of the virus, and thus reduce the economic losses caused by the whitefly through the spread of the virus in the open fields.

Tomato yellow leaf curl virus (TYLCV) causes significant yield loss in tomato production in the southeastern United States and elsewhere. TYLCV is transmitted by the whitefly Bemisia tabaci cryptic species in a persistent, circulative, and non-propagative manner. Unexpectedly, transovarial and sexual transmission of TYLCV has been reported for one strain from Israel. In this study, the potential contribution of the B. tabaci B cryptic species transovarial and sexual transmission of TYLCV (Israel strain, Georgia variant, Georgia, USA) to reoccurring outbreaks was investigated by conducting whitefly-TYLCV transmission assays and virus DNA detection using end point PCR, DNA quantitation via real-time PCR, and virion detection by immunocapture PCR. TYLCV DNA was detectable in four, two, and two percent of first-generation fourth-instar nymphs, first-generation adults, and second-generation adults, respectively, following transovarial acquisition. Post-mating between viruliferous counterparts, the virus's DNA was detected in four percent of males and undetectable in females. The accumulation of TYLCV DNA in whiteflies from the transovarial and/or sexual experiments was substantially lower (100 to 1000-fold) compared with whitefly adults allowed a 48-hr acquisition-access period on plants infected with TYLCV. Despite the detection of TYLCV DNA in whiteflies from the transovarial and/or mating experiments, the virions were undetectable by immunocapture PCR-a technique specifically designed to detect virions. Furthermore, tomato test plants exposed to whitefly adults that presumably acquired TYLCV transovarially or through mating remained free of detectable TYLCV DNA. Collectively, the extremely low levels of TYLCV DNA and complete absence of virions detected in whiteflies and the inability of the B. tabaci cryptic species B to transmit TYLCV to test tomato plants following transovarial and mating acquisition indicate that neither transovarial nor sexual transmission of TYLCV are probable or epidemiologically relevant for TYLCV persistence in this pathosystem.

Tomato yellow leaf curl virus (TYLCV), one of the most serious plant viruses in tropical and subtropical regions, is transmitted to host plants by the vector insect Bemisia tabaci. In order to control TYLCV, it is important to identify weed hosts for overwintering TYLCV. Stellaria aquatica, a winter-hardy weed, was found growing with TYLCV-infected tomato plants in greenhouse production. TYLCV was detected in S. aquatica plants by polymerase chain reaction and Southern blot hybridization analysis. The intergenic region nucleotide sequences amplified from TYLCV-infected tomato plants, TYLCV-viruliferous whiteflies, and S. aquatica were identical. During winter (December to February), TYLCV-viruliferous whiteflies and TYLCV-infected tomato plants were removed or absent from greenhouses. However, S. aquatica plants were observed over a period of 10 months from August to May in such greenhouses, and TYLCV was consistently detected in some of these plants. To investigate the transmission of TYLCV from TYLCV-infected S. aquatica plants to healthy tomato plants by whiteflies, TYLCV-infected S. aquatica plants were transplanted to pots in cages with nonviruliferous whiteflies and healthy tomato plants. After 4 weeks, tomato plants developed typical TYLCV disease symptoms, and TYLCV was detected in both whiteflies and tomato plants. These results show that S. aquatica can act as a winter-hardy reservoir for TYLCV, and suggest that this weed could play an important role in overwintering of TYLCV in tomato greenhouses.

The tomato leaf curl New Delhi virus (ToLCNDV), a bipartite begomovirus (family Geminiviridae), poses a significant threat to various horticultural crops in many Asian and Mediterranean countries. Since its identification, the Asian strain of this virus has exhibited severe infectivity and caused high yield loss in tomato and cucurbit production in the Indian subcontinent and other parts of Asia. ToLCNDV-ES, a different strain of ToLCNDV, emerged recently in the Mediterranean Basin and caused significant outbreaks in Cucurbitaceae species but has shown low adaptation to tomatoes. In a field survey, tomato plants infected with this Mediterranean strain were not discovered. Nevertheless, the same field survey revealed that ToLCNDV-ES occurred in natural double infection with tomato yellow leaf curl virus (TYLCV) in tomato plants with an infection ratio of up to 50%. Moreover, results obtained from experiments where tomato plants agro-inoculated simultaneously with infectious clones of ToLCNDV-ES and TYLCV showed that ToLCNDV-ES was detected in tomatoes while synergized with TYLCV with infection ratios similar to those found under field conditions. Quantitative PCR data indicated the highest amount of ToLCNDV in co-infected plants and no significant change in TYLCV titers among the different mixed infections. Moreover, it was ascertained that not all begomoviruses can enhance the infectivity of Mediterranean ToLCNDV isolates in tomato plants. Our study reports a new finding regarding the ToLCNDV-ES response in tomato while synergized with TYLCV with evidence from both field and laboratory conditions.

The name Tomato yellow leaf curl virus (TYLCV) has been applied to a group of virus species of the genus Begomovirus in the family Geminiviridae that cause a similar tomato disease worldwide. In 1995, TYLCV was first reported in Algarve (southern Portugal) as responsible for an epidemic outbreak of a severe tomato disease. Molecular data have shown that this Portuguese TYLCV isolate was distinct from those previously reported in Europe, as it belonged to the TYLCV‐Israel species1. Since then, TYLCV epidemics have occurred annually, being a limiting factor mainly for autumn/winter glasshouse tomato crops. In 1998, TYLCV was also found associated with the emergence of a novel disease of Phaseolus vulgaris in Algarve. The affected bean plants were severely stunted and gave no marketable yield. However, the disease occurs only sporadically, even in conditions of high TYLCV infection pressure. Recently, Tomato chlorosis virus (ToCV), a whitefly‐transmitted bipartite closterovirus (genus Crinivirus, family Closteroviridae), was found associated with an unusual tomato yellow leaf syndrome, in single or mixed infection with TYLCV. The impact of this new pathosystem on tomato production has yet to be determined. Surveys are in progress in mixed cropping systems infested with whiteflies. So far, TYLCV and ToCV diseases are limited to the Algarve region.

Tomato yellow leaf curl virus (TYLCV) causes great losses in tomato production. In addition to tomato, TYLCV infects many crops or weeds as alternative hosts. These alternative hosts may serve as reservoirs for TYLCV survival and spread. Here, we tested the capability of cultivated, flue-cured tobacco to act as a reservoir host plant for TYLCV. TYLCV DNA was detected in nine flue-cured tobacco cultivars inoculated with an infectious TYLCV clone, although no visible symptoms developed on TYLCV-infected tobacco plants. The percentage of whiteflies with viral DNA increased with an increasing acquisition access period (AAP) and reached 100% after a 12 h AAP on infected tobacco plants. Using infected tobacco plants as virus resources, TYLCV was capable of being transmitted to tobacco and tomato plants by whiteflies, and typical symptoms of TYLCV infection were observed on infected tomato plants but not on infected tobacco plants. Our results suggest that flue-cured tobacco can serve as a reservoir host plant for TYLCV and may play an important role in the spread of TYLCV epidemics in China.

Epidemics of tomato yellow leaf curl disease (TYLCD) in the Dominican Republic in the early to mid-1990s resulted in catastrophic losses to processing tomato production. As part of an integrated management approach to TYLCD, the complete nucleotide sequence of a full-length infectious clone of an isolate of Tomato yellow leaf curl virus (TYLCV) from the Dominican Republic (TYLCV-[DO]) was determined. The TYLCV-[DO] genome was nearly identical in sequence (>97%) and genome organization to TYLCV isolates from Israel and Cuba. This established that TYLCV-[DO] is a bonafide TYLCV isolate (rather than a recombinant virus, such as isolates from Israel [Mild], Portugal, Japan, and Iran), and provided further evidence for the introduction of the virus from the eastern Mediterranean. A reduction in the incidence of TYLCV in the northern and southern processing tomato production areas of the Dominican Republic has been associated with the implementation of a mandatory 3-month whitefly host-free period (including tomato, common bean, cucurbits, eggplant, and pepper). Monitoring TYLCV levels in whiteflies, by polymerase chain reaction with TYLCV-specific primers, established that the incidence of TYLCV decreased markedly during the host-free period, and then gradually increased during the tomato-growing season. In contrast, TYLCV persisted in whiteflies and tomato plants in an area in which the host-free period was not implemented. Surveys for TYLCV reservoir hosts, conducted to identify where TYLCV persists during the host-free period, revealed symptomless infections in a number of weed species. The implications of these findings for TYLCV management in the Dominican Republic are discussed.

Numerous animal and plant viruses are transmitted by arthropod vectors in a persistent, circulative manner. Tomato yellow leaf curl virus (TYLCV) is transmitted by the sweet potato whitefly Bemisia tabaci. We report here that infection with Rickettsia spp., a facultative endosymbiont of whiteflies, altered TYLCV-B. tabaci interactions. A B. tabaci strain infected with Rickettsia acquired more TYLCV from infected plants, retained the virus longer, and exhibited nearly double the transmission efficiency compared to an uninfected B. tabaci strain with the same genetic background. Temporal and spatial antagonistic relationships were discovered between Rickettsia and TYLCV within the whitefly. In different time course experiments, the levels of virus and Rickettsia within the insect were inversely correlated. Fluorescence in situ hybridization analysis of Rickettsia-infected midguts provided evidence for niche exclusion between Rickettsia and TYLCV. In particular, high levels of the bacterium in the midgut resulted in higher virus concentrations in the filter chamber, a favored site for virus translocation along the transmission pathway, whereas low levels of Rickettsia in the midgut resulted in an even distribution of the virus. Taken together, these results indicate that Rickettsia, by infecting the midgut, increases TYLCV transmission efficacy, adding further insights into the complex association between persistent plant viruses, their insect vectors, and microorganism tenants that reside within these insects. Interest in bacterial endosymbionts in arthropods and many aspects of their host biology in agricultural and human health systems has been increasing. A recent and relevant studied example is the influence of Wolbachia on dengue virus transmission by mosquitoes. In parallel with our recently studied whitefly-Rickettsia-TYLCV system, other studies have shown that dengue virus levels in the mosquito vector are inversely correlated with bacterial load. Our work here presents evidence of unifying principles between vectors of plant and animal viruses in a role for endosymbionts in manipulating vector biology and pathogen transmission. Our results demonstrate the influence of an interesting and prominent bacterial endosymbiont in Bemisia tabaci in TYLCV transmission, a worldwide disease infecting tomatoes. Besides its agricultural importance, this system provides interesting insights into Bemisia interaction with these newly discovered endosymbionts.

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.