Tomato Yellow Leaf Curl Disease Research Articles

Plant Growth, Fruit Yield, and Tomato Leaf Curl Disease of High Tunnel Organic Tomato Affected by Shade Net and Plastic Mulch Color

There is an increasing interest in producing organic tomatoes (Solanum lycopersicum) in high tunnels (HTs) in the southeast United States. HTs are unheated, passively cooled structures that allow tomato growers to harvest high-quality fruit out of season. However, excessive temperatures inside HTs may negatively impact tomato plant growth and fruit yield. Shade nets have been reported to reduce temperatures inside the HTs. Plastic mulch color has also significantly influenced plant growth and yield under high-temperature conditions. This study aimed to determine the effects of shade net color and plastic mulch color on plant growth, fruit yield, and incidence of tomato yellow leaf curl disease (TYLC) in ‘Red Snapper’ tomato grown in HTs under elevated temperatures (summer-fall) in southern Georgia, USA. Organic ‘Red Snapper’ tomato seedlings were transplanted in HTs in 2019 (Season 1) and 2020 (Season 2). The design was a split-plot randomized block where the main plots were externally mounted shade nets (black, silver, and unshaded; 30% shade factor), and the subplots were plastic mulches (black and white). Compared with black mulch, white mulch improved plant height and stem diameter but did not influence fruit yields. Shade nets reduced HT air temperature and root zone temperature (RZT) but did not affect plant height and stem diameter. The diminished photosynthetic photon flux density (PPFD) under the shade nets reduced marketable fruit yield. Thus, shade nets are not recommended once heat challenges do not limit HT tomato production in Georgia (after about mid-October). Shade nets and plastic mulch inconsistently affected TYLC incidence, severity, and area under the disease progress curve (AUDPC). Additional fruit yield reductions occurred due to TYLC because the incidence was 100% 6 weeks after transplanting. Preliminary insect data showed that shade net treatments had similar sweetpotato whitefly (Bemisia tabaci) numbers. The high TYLC incidence indicates that ‘Red Snapper’ may not be suitable for fall HT tomato production in the southeast United States. More research on shading and heat stress management in HT organic tomato production is necessary.

Breakdown of Ty-1-Based Resistance to Tomato Yellow Leaf Curl Virus in Tomato Plants at High Temperatures.

The global dissemination of the Israel (IL) and mild (Mld) strains of tomato yellow leaf curl virus (TYLCV) (family Geminiviridae, genus Begomovirus) is a major threat to tomato production in many regions worldwide. The use of resistant hybrid cultivars bearing the dominant resistance genes Ty-1, Ty-3, and Ty-3a has become a common practice for controlling tomato yellow leaf curl disease (TYLCD) caused by TYLCV. However, TYLCD symptoms have been sporadically observed in resistant cultivars grown in seasons when temperatures are high. In this study, we used TYLCV-resistant cultivars with confirmed presence of Ty-1, which were determined using newly developed allele-specific markers based on polymorphisms within the locus. These Ty-1-bearing resistant tomato plants and susceptible plants were infected with TYLCV and grown at moderate or high temperatures. Under high-temperature conditions, the Ty-1-bearing tomato cultivar Momotaro Hope (MH) infected with TYLCV-IL had severe TYLCD symptoms, which were almost equivalent to those of the susceptible cultivar. However, MH plants infected with TYLCV-Mld were symptomless or had slight symptoms under the same temperature condition. The quantitative analysis of the TYLCV-IL viral DNA content revealed a correlation between symptom development and viral DNA accumulation. Furthermore, under high-temperature conditions, TYLCV-IL caused severe symptoms in multiple commercial tomato cultivars with different genetic backgrounds. Our study provided the scientific evidence for the experientially known phenomenon by tomato growers, and it is anticipated that global warming, associated with climate change, could potentially disrupt the management of TYLCV in tomato plants mediated by the Ty-1 gene.

Phenotype and signaling pathway analysis to explore the interaction between tomato plants and TYLCV in different organs

Tomato yellow leaf curl disease (TYLCD), caused by Tomato yellow leaf curl virus (TYLCV), is one of the most destructive diseases in tomato cultivation. By comparing the phenotypic characteristics and virus quantities in the susceptible variety 'Cooperation 909 Red Tomatoes' and the resistant variety 'Huamei 204' after inoculation with TYLCV infectious clones, our study discovered that the root, stem and leaf growth of the susceptible variety 'Cooperation 909 Red Tomatoes' were severely hindered and the resistant variety 'Huamei 204' showed growth inhibition only in roots. TYLCV accumulation in roots were significantly higher than in leaves. Further, we examined the expression of key genes in the SA and JA signalling pathways in leaves, stems and roots and found the up-regulation of SA-signalling genes in all organs of the susceptible variety after inoculation with TYLCV clones. Interestingly, SlJAZ2 in roots of the resistant variety was significantly down-regulated upon TYLCV infection. Further, we silenced the SlNPR1 and SlCOI1 genes individually using virus induced gene silencing system in tomato plants. We found that viruses accumulated to a higher level in SlNPR1 silenced plants than wild type plants, and the virus quantity in roots was significantly increased in SlCOI1 silenced plants. These results provide new insights for advancing research in understanding tomato-TYLCV interaction.

Differential Effects of Two Tomato Begomoviruses on the Life History and Feeding Preference of Bemisia tabaci.

Tomato yellow leaf curl disease, caused by a group of closely related tomato yellow leaf curl viruses, is a major threat to tomato cultivation worldwide. These viruses are primarily transmitted by the sweet potato whitefly (Bemisia tabaci) in a persistent-circulative manner, wherein the virus circulates in the body of B. tabaci and infects its tissues. The complex relationship between viruses and whiteflies significantly influences virus transmission, with studies showing varying effects of the former on the life history and feeding preference of the latter. Whether these effects are direct or indirect, and whether they are negative, neutral, or positive, appears to depend on the specific interactions between virus and whitefly species. The tomato yellow leaf curl Thailand virus (TYLCTHV) and the tomato leaf curl Taiwan virus (ToLCTV) are two prevalent begomoviruses in fields in Taiwan. This study examined the direct and indirect effects of TYLCTHV and ToLCTV on the life history traits (longevity, fecundity, nymph survival, and nymph developmental time) and feeding preference of B. tabaci Middle East-Asia Minor 1 (MEAM1). The results revealed that TYLCTHV had no effects on these life history traits or the feeding preference of MEAM1 whiteflies. Although ToLCTV did not directly affect the longevity and fecundity of MEAM1 whiteflies, their fecundity and the nymph developmental time were negatively affected by feeding on ToLCTV-infected plants. In addition, ToLCTV infection also altered the feeding preference of MEAM1 whiteflies. The different effects of virus infection may contribute to the lower prevalence of ToLCTV compared to TYLCTHV in fields in Taiwan.

Large Artificial microRNA Cluster Genes Confer Effective Resistance against Multiple Tomato Yellow Leaf Curl Viruses in Transgenic Tomato.

Tomato yellow leaf curl disease (TYLCD) has become the key limiting factor for the production of tomato in many areas because of the continuous infection and recombination of several tomato yellow leaf curl virus (TYLCV)-like species (TYLCLV) which produce novel and destructive viruses. Artificial microRNA (AMIR) is a recent and effective technology used to create viral resistance in major crops. This study applies AMIR technology in two ways, i.e., amiRNA in introns (AMINs) and amiRNA in exons (AMIEs), to express 14 amiRNAs targeting conserved regions in seven TYLCLV genes and their satellite DNA. The resulting pAMIN14 and pAMIE14 vectors can encode large AMIR clusters and their function in silencing reporter genes was validated with transient assays and stable transgenic N. tabacum plants. To assess the efficacy of conferring resistance against TYLCLV, pAMIE14 and pAMIN14 were transformed into tomato cultivar A57 and the resulting transgenic tomato plants were evaluated for their level of resistance to mixed TYLCLV infection. The results suggest that pAMIN14 transgenic lines have a more effective resistance than pAMIE14 transgenic lines, reaching a resistance level comparable to plants carrying the TY1 resistance gene.

Tomato Yellow Leaf Curl Sardinia Virus Increases Drought Tolerance of Tomato.

Drought stress is one of the major physiological stress factors that adversely affect agricultural production, altering critical features of plant growth and metabolism. Plants can be subjected simultaneously to abiotic and biotic stresses, such as drought and viral infections. Rewarding effects provided by viruses on the ability of host plants to endure abiotic stresses have been reported. Recently, begomoviruses causing the tomato yellow leaf curl disease in tomatoes were shown to increase heat and drought tolerance. However, biological bases underlying the induced drought tolerance need further elucidation, particularly in the case of tomato plants. In this work, tomato plants infected by the tomato yellow leaf curl Sardinia virus (TYLCSV) were subjected to severe drought stress, followed by recovery. Morphological traits, water potential, and hormone contents were measured in leaves together with molecular analysis of stress-responsive and hormone metabolism-related genes. Wilting symptoms appeared three days later in TYLCSV-infected plants compared to healthy controls and post-rehydration recovery was faster (2 vs. 4 days, respectively). Our study contributes new insights into the impact of viruses on the plant's adaptability to environmental stresses. On a broader perspective, such information could have important practical implications for managing the effects of climate change on agroecosystems.

Crinivirus Tomato Chlorosis Virus Compromises the Control of Tomato Yellow Leaf Curl Virus in Tomato Plants by the Ty-1 Gene.

Tomato yellow leaf curl disease (TYLCD) causes severe damage to tomato crops in warm regions of the world, and is associated with infections of several whitefly (Bemisia tabaci)-transmitted single-stranded (ss)DNA begomoviruses (genus Begomovirus, family Geminiviridae). The most widespread begomovirus isolates associated with TYLCD are those of the type strain of the Tomato yellow leaf curl virus species, known as Israel (TYLCV-IL). The Ty-1 gene is widely used in commercial tomato cultivars to control TYLCV-IL damage, providing resistance to the virus by restricting viral accumulation and tolerance to TYLCD by inhibiting disease symptoms. However, several reports suggest that TYLCV-IL-like isolates are adapting to the Ty-1 gene and are causes of concern for possibly overcoming the provided control. This is the case with TYLCV-IL IS76-like recombinants that have a small genome fragment acquired by genetic exchange from an isolate of Tomato yellow leaf curl Sardinia virus, another begomovirus species associated with TYLCD. Here we show that TYLCV-IL IS76-like isolates partially break down the TYLCD-tolerance provided by the Ty-1 gene and that virulence differences might exist between isolates. Interestingly, we demonstrate that mixed infections with an isolate of the crinivirus (genus Crinivirus, family Closteroviridae) species Tomato chlorosis virus (ToCV), an ssRNA virus also transmitted by B. tabaci and emerging worldwide in tomato crops, boosts the breakdown of the TYLCD-tolerance provided by the Ty-1 gene either with TYLCV-IL IS76-like or canonical TYLCV-IL isolates. Moreover, we demonstrate the incorporation of the Ty-2 gene in Ty-1-commercial tomatoes to restrict (no virus or virus traces, no symptoms) systemic infections of recombinant TYLCV-IL IS76-like and canonical TYLCV-IL isolates, even in the presence of ToCV infections, which provides more robust and durable control of TYLCD.

A meta-analysis of climatic conditions and whitefly Bemisia tabaci population: implications for tomato yellow leaf curl disease

BackgroundTomato yellow leaf curl disease (TYLCD), which is caused by the genus Begomovirus, is basically transmitted by the vector whitefly, Bemisia tabaci (B. tabaci). It remains a destructive disease of tomato across the world. The disease is present in many tomato growing countries, and it has a broad geographical distribution. The population and distribution of the vector are therefore an important factor in disease spread. This study assesses the determinants of the relationship between climatic factors and whitefly population. A thorough search of relevant papers was first initiated, and eventually 16 articles with 142 estimates were selected. A meta-regression analysis, especially the random-effects model with a restricted maximum likelihood (REML) estimator, was applied.ResultsSummarization of effect sizes revealed a mean effect size for the study of r = 0.15. The forest plot suggested a significant amount of study heterogeneity. No evidence of significant publication bias was uncovered. The meta-analysis revealed that the population of whiteflies was significantly related to climatic independent variables such as maximum and minimum temperature and rainfall. Other factors such as altitude, number of symptoms, pesticide policy, type of soil, number of references, impact factor and publication status were found to significantly influence the effect sizes.ConclusionsWhiteflies are playing a major role in spreading the TYLCD. Several factors were identified to have a significant impact on the climatic conditions-whitefly population nexus. Since climatic factors, altitude, existing pesticide laws and type of soil were found to have a significant impact on the effect sizes, agricultural management policies could be enacted by specifically considering those factors in a view to minimize the impact of whiteflies. In general, all the above factors could be considered in strategy to manage TYLCD.

Behavior of new entries and developed tomato hybrids carrying Ty-2 genes

Tomato yellow leaf curl disease (TYLCD) is a serious problem hampering tomato production worldwide. In the Mediterranean Basin, disease incidence and severity are higher in the dry season increasing whitefly (Bemisia tabaci) populations. Effectiveness of resistance to Tomato yellow leaf curl virus (TYLCV) depends on both tomato host resistance and TYLCV complex species. So far, six different Ty tomato resistance genes have been identified. Two main TYLCV complex species, Tomato yellow leaf curl virus-Israel (TYLCV-Is) and Tomato yellow leaf curl Sardinia virus (TYLCSV), have been identified in Tunisia. The present work aimed to evaluate entries heterozygous for Ty-2 gene to help predict hybrid performance. Two tomato entries homozygous for the Ty-2 TYLCV resistance gene, one tomato hybrid homozygous for Ty-2 and two heterozygous hybrids were included, besides two susceptible tomato entries. Resistance response to TYLCD was recorded based on disease incidence and severity levels. Data analysis was performed according to presence/absence of Ty-2 gene and taking into account homozygosity and heterozygosity of Ty-2. Generalized linear model analysis was applied to check significance of individual factors' effects (i.e. effect of tomato entries or tomato groups of entries based on presence or absence of homozygous/heterozygous Ty-2 gene, block unit within the field trial and the year of the trial) on the dependent variables (disease incidence and severity). Further multicomparison tests gave evidence on significant effect of Ty-2 homozygous gene tomato entries on TYLCD incidence and severity levels. The results were discussed with special focus on the relevance use of heterozygous hybrid tomato varieties.

The invasion biology of tomato begomoviruses in Costa Rica reveals neutral synergism that may lead to increased disease pressure and economic loss

Since the late 1980s, tomato production in Costa Rica has been affected by diseases caused by whitefly-transmitted begomoviruses. The first was tomato yellow mottle virus (ToYMoV), a locally evolved New World (NW) bipartite begomovirus associated with the tomato yellow mottle disease (ToYMoD). In the late 1990s, the invasive NW bipartite tomato leaf curl Sinaloa virus (ToLCSiV) was detected in Costa Rica and has become established and associated with ToYMoD. Finally, the invasive Old World (OW) monopartite tomato yellow leaf curl virus (TYLCV) was detected in Costa Rica in 2012 and has also become established and is causing tomato yellow leaf curl disease (TYLCD). In the present study, we investigated the invasion biology of these tomato-infecting begomoviruses in Costa Rica in terms of (i) their biological and genetic properties and (ii) disease symptoms and viral DNA accumulation in tomato plants having single and mixed infections. We first generated infectious DNA-A and DNA-B clones and agroinoculation systems for ToYMoV and ToLCSiV isolates recovered from archival ToYMoD samples collected in Costa Rica in 1990 and 2002, respectively. Tomato plants agroinoculated with the infectious clones of both viruses developed ToYMoD symptoms, completing Koch's postulates for ToYMoV, and showing that ToLCSiV also causes this disease. However, pseudorecombinants formed between the DNA components of these viruses were not infectious, which is consistent with independent evolution in different lineages and limits genetic interactions. Furthermore, ToYMoV is well-adapted to tomato, has a narrow host range and is mechanically transmissible. The DNA-A component has a recombination event in the hot spot area and induced a symptomless infection in agroinoculated Nicotiana benthamiana and tomato plants. Tomato plants co-infected with two or all three viruses developed more severe symptoms compared with plants infected with each virus alone. Symptoms induced by the NW bipartite ToYMoV and ToLCSiV appeared earlier (∼7 d post-inoculation [dpi]) than those induced by TYLCV (∼10 dpi), but TYLCD symptoms became predominant in single and mixed infections by 14 dpi. Viral DNA accumulation was quantified by qPCR and generally revealed a neutral synergistic interaction in which the viruses co-existed in mixed infections. A transient reduction in accumulation of ToYMoV and ToLCSiV was detected in mixed infections at 7 dpi, whereas TYLCV accumulation was not affected in mixed infections and was uniform among treatments and time points. Together our results suggest that this neutral synergistic interaction will lead to increased begomovirus disease severity in Costa Rica. We discuss this in terms of begomovirus invasion biology and disease management.

The C4 protein of tomato yellow leaf curl Sardinia virus primes drought tolerance in tomato through morphological adjustments.

Viruses can interfere with the ability of plants to overcome abiotic stresses, indicating the existence of common molecular networks that regulate stress responses. A begomovirus causing the tomato yellow leaf curl disease was recently shown to enhance heat tolerance in tomato and drought tolerance in tomato and Nicotiana benthamiana and experimental evidence suggested that the virus-encoded protein C4 is the main trigger of drought responses. However, the physiological and molecular events underlying C4-induced drought tolerance need further elucidation. In this study, transgenic tomato plants expressing the tomato yellow leaf curl Sardinia virus (TYLCSV) C4 protein were subjected to severe drought stress, followed by recovery. Morphometric parameters, water potential, gas exchanges, and hormone contents in leaves were measured, in combination with molecular analysis of candidate genes involved in stress response and hormone metabolism. Collected data proved that the expression of TYLCSV C4 positively affected the ability of transgenic plants to tolerate water stress, by delaying the onset of stress-related features, improving the plant water use efficiency and facilitating a rapid post-rehydration recovery. In addition, we demonstrated that specific anatomical and hydraulic traits, rather than biochemical signals, are the keynote of the C4-associated stress resilience. Our results provide novel insights into the biology underpinning drought tolerance in TYLCSV C4-expressing tomato plants, paving the way for further deepening the mechanism through which such proteins tune the plant-virus interaction.

Marker assisted detection of TYLCV and late blight resistance in tomato (Solanum lycopersicum)

Marker assisted breeding relies on the identification of genetic loci linked to desirable genes/alleles and is beingutilized for selecting desirable traits including disease resistance in a wide variety of crops. The tomato (Solanumlycopersicum L.) production worldwide has lately been threatened by outbreaks of tomato yellow leaf curl virustransmitted by the whitefly (Bemisia tabaci) and late blight caused by oomycete pathogen Phytophthora infestans(Mont.) de Bary. Resistance genes against both pathogens are available and widely used in tomato breeding throughoutthe world. Molecular markers for resistance alleles greatly enhance selection of resistant plants. For effective breedingprogramme, the validation of markers linked to resistance genes in tomato was carried out for tomato improvement.For this purpose, available markers for the tomato yellow leaf curl disease resistance gene loci Ty-2, Ty3, Ty3a andlate blight resistant loci Ph3 were validated. The assay correctly predicted the genotypes of tomato breeding linesharbouring resistance allele at each loci. Further a multiplex assay was also standardized to simultaneously detectthe presence of resistant/susceptible alleles at Ty2,Ty3 and Ty3a loci. The present study carried out in the Division ofVegetable Science, ICAR-IARI, New Delhi, demonstrates the feasibility of combining two SCAR markers (TG0302and P6-25) for detecting simultaneously three important resistance gene loci in tomato genotypes and thereby improvingthe cost and efficiency of the assay.

Effect of tomato yellow leaf curl disease on yield, height and chlorophyll of open field grown tomato genotypes in Oman

Effect of tomato yellow leaf curl disease on yield, height and chlorophyll of open field grown tomato genotypes in Oman

Fungal F8-Culture Filtrate Induces Tomato Resistance against Tomato Yellow Leaf Curl Thailand Virus

Tomato (Solanum lycopersicum) is an important economic crop worldwide. However, tomato production is jeopardized by the devastating tomato yellow leaf curl disease caused by whitefly-transmitted begomoviruses (WTBs). In this study, we evaluated the efficacy of our previously developed plant antiviral immunity inducer, fungal F8-culture filtrate, on tomato to combat tomato yellow leaf curl Thailand virus (TYLCTHV), the predominant WTB in Taiwan. Our results indicated that F8-culture filtrate treatment induced strong resistance, did not reduce the growth of tomato, and induced prominent resistance against TYLCTHV both in the greenhouse and in the field. Among TYLCTHV-inoculated Yu-Nu tomato grown in the greenhouse, a greater percentage of plants treated with F8-culture filtrate (43–100%) were healthy-looking compared to the H2O control (0–14%). We found that TYLCTHV cannot move systemically only on the F8-culture filtrate pretreated healthy-looking plants. Tracking the expression of phytohormone-mediated immune maker genes revealed that F8-culture filtrate mainly induced salicylic acid-mediated plant immunity. Furthermore, callose depositions and the expression of the pathogen-induced callose synthase gene, POWDERY MILDEW RESISTANT 4 were only strongly induced by TYLCTHV on tomato pretreated with F8-culture filtrate. This study provides an effective way to induce tomato resistance against TYLCTHV.

No Evidence for Seed Transmission of Tomato Yellow Leaf Curl Sardinia Virus in Tomato

Seed transmission is an important factor in the epidemiology of plant pathogens. Geminiviruses are serious pests spread in tropical and subtropical regions. They are transmitted by hemipteran insects, but a few cases of transmission through seeds were recently reported. Here, we investigated the tomato seed transmissibility of the begomovirus tomato yellow leaf curl Sardinia virus (TYLCSV), one of the agents inducing the tomato yellow leaf curl disease, heavily affecting tomato crops in the Mediterranean area. None of the 180 seedlings originating from TYLCSV-infected plants showed any phenotypic alteration typical of virus infection. Moreover, whole viral genomic molecules could not be detected in their cotyledons and true leaves, neither by membrane hybridization nor by rolling-circle amplification followed by PCR, indicating that TYLCSV is not a seed-transmissible pathogen for tomato. Examining the localization of TYLCSV DNA in progenitor plants, we detected the virus genome by PCR in all vegetative and reproductive tissues, but viral genomic and replicative forms were found only in leaves, flowers and fruit flesh, not in seeds and embryos. Closer investigations allowed us to discover for the first time that these embryos were superficially contaminated by TYLCSV DNA but whole genomic molecules were not detectable. Therefore, the inability of TYLCSV genomic molecules to colonize tomato embryos during infection justifies the lack of seed transmissibility observed in this host.

The Global Dimension of Tomato Yellow Leaf Curl Disease: Current Status and Breeding Perspectives.

Tomato yellow leaf curl disease (TYLCD) caused by tomato yellow leaf curl virus (TYLCV) and a group of related begomoviruses is an important disease which in recent years has caused serious economic problems in tomato (Solanum lycopersicum) production worldwide. Spreading of the vectors, whiteflies of the Bemisia tabaci complex, has been responsible for many TYLCD outbreaks. In this review, we summarize the current knowledge of TYLCV and TYLV-like begomoviruses and the driving forces of the increasing global significance through rapid evolution of begomovirus variants, mixed infection in the field, association with betasatellites and host range expansion. Breeding for host plant resistance is considered as one of the most promising and sustainable methods in controlling TYLCD. Resistance to TYLCD was found in several wild relatives of tomato from which six TYLCV resistance genes (Ty-1 to Ty-6) have been identified. Currently, Ty-1 and Ty-3 are the primary resistance genes widely used in tomato breeding programs. Ty-2 is also exploited commercially either alone or in combination with other Ty-genes (i.e., Ty-1, Ty-3 or ty-5). Additionally, screening of a large collection of wild tomato species has resulted in the identification of novel TYLCD resistance sources. In this review, we focus on genetic resources used to date in breeding for TYLCVD resistance. For future breeding strategies, we discuss several leads in order to make full use of the naturally occurring and engineered resistance to mount a broad-spectrum and sustainable begomovirus resistance.

Vector Transmission of Tomato Yellow Leaf Curl Thailand Virus by the Whitefly Bemisia tabaci: Circulative or Propagative?

Simple SummaryTomato yellow leaf curl viruses cause disease epidemics in tomato crops in tropical and subtropical areas worldwide. The sweet potato whitefly, Bemisia tabaci, is a vector of this group of viruses. This research studied the transmission biology of tomato yellow leaf curl Thailand virus (TYLCTHV) by B. tabaci, including virus-infected tissues, virus translocation, virus replication, and transovarial transmission (i.e., transmission from mother to progeny via ovaries). We discovered that the virus first infects the alimentary gut, then the hemolymph, and finally the salivary glands of the whitefly. The virus did not replicate in the whitefly during infection. In addition, TYLCTHV was detected in only 10% of infected females’ first-generation progeny, but the progeny was unable to cause viral infection of tomato plants; therefore, there was no evidence of transovarial transmission. When combined with the current literature, our results suggest that B. tabaci transmits TYLCTHV in a persistent-circulative mode.Viruses that cause tomato yellow leaf curl disease are part of a group of viruses of the genus Begomovirus, family Geminiviridae. Tomato-infecting begomoviruses cause epidemics in tomato crops in tropical, subtropical, and Mediterranean climates, and they are exclusively transmitted by Bemisia tabaci in the field. The objective of the present study was to examine the transmission biology of the tomato yellow leaf curl Thailand virus (TYLCTHV) by B. tabaci, including virus-infected tissues, virus translocation, virus replication, and transovarial transmission. The results demonstrated that the virus translocates from the alimentary gut to the salivary glands via the hemolymph, without apparent replication when acquired by B. tabaci. Furthermore, the virus was detected in 10% of the first-generation progeny of viruliferous females, but the progeny was unable to cause the viral infection of host plants. There was no evidence of transovarial transmission of TYLCTHV in B. tabaci. When combined with the current literature, our results suggest that B. tabaci transmits TYLCTHV in a persistent-circulative mode. The present study enhances our understanding of virus–vector interaction and the transmission biology of TYLCTHV in B. tabaci.

Comparative Efficacy of Silver Metallic Plastic Mulch, Botanicals and Insecticides in Controlling Tomato Yellow Leaf Curl Disease

Tomato Yellow Leaf Curl caused by Tomato Yellow Leaf Curl Virus (TYLCV) is one of the most important diseases of tomato causing heavy losses in yield and quality of fruits. Damage caused through phloem feeding and transmission of TYLCV by the insect vectors whitefly (Bemisiatabaci). In this study the competence of silver metallic plastic mulch, botanicals and insecticides were assessed to manage the Tomato Yellow Leaf Curl Virus (TYLCV) by controlling the insect vectors. In total 7 treatments including control were considered viz. T1=Imidacloprid, T2= ACmix, T3= Subicron, T4= Neemax, T5= Multineem, T6 = Silver metallic plastic mulch and T7= Control. All the treatments showed significant influence on different assayed parameters in the test crop tomato. The lowest disease incidence, disease severity and whitefly association was found in T6 treatment (silver metallic plastic mulch) that was 2.87%, 1.72% and 2.0% at 60 days after transplanting (DAT) respectively. While the highest disease incidence, disease severity and whitefly association were found in T7 treatment (control treatment) that was 14.71%, 46.22% and 18, respectively, at 60 DAT. From the relationship study between disease incidence and disease severity with whitefly association, it was revealed that disease incidence and severity of TYLCV was increased with increasing of whitefly population and vice-versa. Among the treatments, growth parameters, yield and yield attributers were also found better in T6treatment (silver metallic plastic mulch). Silver metallic plastic mulch is the best option to manage the TYLCV by controlling the insect vectors, whitefly instead of insecticides.
 SAARC J. Agri., 18(2): 77-86 (2020)

BEGOMOVIRUSES AND BETASATELLITES ASSOCIATED WITH CLCuD

Begomoviruses are one of the major types of plant viruses. They are transmitted by whitefly and cause many diseases. The CLCuD is the most damaging disease of cotton. It is the vector of begomoviruses, namely as monpartite or bipartite begomoviruses. Bipartite begomoviruses are consisted of A and B DNA molecuales. Monopatite consist of single genome. It is mainly linked with alphasatellites and betasatellites. Alphasatellites can replicate by using replication protein and not called as true satellites. Betasatellites are called as true satellites as they are linked with alphasatellites. Mainly cause tomato yellow leaf curl disease. Begomoviruses are different from other plant viruses as the basis of RNA genomes. DNA beta satellite is involves in suppressing the expressions of genes in plants. It has a major role in preventing RNA silencing by encoding proteins that binds with DNA and target the nucleus of cell. Affected plants show various symptoms such as leaf curling, enations etc. that cause loss in cotton field by preventing the growth. With the help of PCR, 1.4 kb fragments of DNA have been amplified from DNA template. For cloning the whole begomoviruses genome, a simple method of cloning has been widely used. Cloning is usually done by using the bacteriophage DNA polymerase. The betasatellites have shown association with CLCuD.

Pyramiding Ty-1/Ty-3, Ty-2, ty-5 and ty-6 genes into tomato hybrid to develop resistance against tomato leaf curl viruses and recurrent parent genome recovery by ddRAD sequencing method

Tomato leaf curl virus (ToLCV) is a begomovirus transmitted by whitefly (Bemisia tabaci) and causes Tomato (yellow) leaf curl disease (TYLCD/ToLCD) in many parts of India and rest of the world resulting in huge economic losses. Many Ty genes identified either from wild and/or cultivated tomato, which confers various levels of resistance to ToLCV. The current study aimed at stacking four important resistant genes (Ty-1/Ty-3, Ty-2, ty-5, and ty-6) in parental lines of a commercial tomato hybrid JKTH811 with the aid of the marker-assisted backcross breeding program. As a donor source, two pre-breeding lines, CLN3125K (Ty-1/Ty-3 and Ty-2) and FLA456 (ty-5 and ty-6) was used. Crossed population screened by using tightly linked Ty genes specific markers for foreground selection and attempted the fastest recovery of recurrent parental genome through NGS based ddRAD sequencing approach. Ty genes introgressed parental lines as well as the resulting F1 hybrids were tested for their bio-efficacy against ToLCNDV (New Delhi var.) under greenhouse and field conditions. Disease severity of Ty genes pyramided female lines and F1 hybrids were found as significantly lower when compared to original parental lines and hybrid. This report demonstrates the efficiency of Ty genes pyramiding from different donors in a hybrid against ToLCV and recovery of the recurrent genome using the ddRAD-seq platform in the minimum generations possible.