Tomato Leaf Curl Disease Research Articles

Infection of tomato in Iraq with tomato leaf curl Palampur virus and multiple variants of tomato yellow leaf curl virus

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.

Efficacy assessment of different insecticides for control of whitefly against tomato leaf curl disease

AbstractThe impact of eight pesticides on the transmission of Tomato leaf curl virus (ToLCV) by the whitefly, Bemisia tabaci Gennadius to tomato, Lycopersicon esculentum (Miller), was studied in the field using a randomized block design. Differences in performance were anticipated because these eight insecticides comprise distinct mechanism of action including both contact and systemic. Increased insecticide efficacy is necessary, particularly in regions with conducive weather conditions that support a healthy whitefly population, to effectively manage the population. There is a need to vary the insecticides used in order to reduce the emergence of resistance in the whitefly population due to the extensive usage of a single mechanism of action for whitefly control. The foliar spray of insecticides was done when first incidence of whitefly was noticed in the field with 15 days of interval. The studies on effect of different insecticides in the management of ToLCV disease through the controlling whitefly population, we evaluated that Chlorantraniliprole 8.8% + Thiomethaxam 17.5% SC was effective in sustaining the yield by reducing the incidence of disease and whitefly population during both the years followed by Spirotetramat 11.01% + Imidacloprid 11.01% SC, Thiamethoxam 12.6% + Lambda cyhalothrin 9.5% ZC and Cyantraniliprole 10.26% OD, respectively.

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.

Phylo-geographic analysis of whitefly on the basis of mitochondrial cytochrome oxidase 1 gene

Abstract Bemisia tabaci is a species complex that causes damage to its broad range of plant hosts through serious feeding. It transmits plant viruses of different groups to important agricultural crops. Some important cash crops of Pakistan are sugar cane, rice, tobacco and seed oil. It shows high genetic variability and is differentiated as races or biotypes. Biotypes are, biotype Q, biotype B, biotype B2, biotype M, biotype L, biotype A, biotype H, biotype C, biotype K, biotype N, biotype R, biotype E, biotype P, biotype J, biotype S, biotype AN. Although the current report based on the Bayesian study of mitochondrial cytohrome oxidase gene1 (CO1) DNA sequences has classified the different populations of whiteflies into twelve genetic groups which are Mediterranean, Sub-Saharan Africa silverleafing, Indian Ocean, Asia II, Asia I, Australia, New World, Italy, China, Sub-Saharan Africa non-silverleafing, Mediterranean/Asia Minor/Africa and Uganda sweet potato. Begomoviruses is largest group of viruses transmitted by B. tabaci and cause major diseases of crops such as tomato and chili leaf curl disease, cassava mosaic disease; yellow mosaic disease of legumes and cotton leaf curl disease. The main objective of current study is to inculpate knowledge regarding genetic diversity of whitefly in cotton fields across Pakistan via analysis of partial DNA sequence of mitochondrial gene Cytochrom Oxidase I (mtCO1).

Diverse begomovirus-betasatellite complexes cause tomato leaf curl disease in the western India

In the Indian sub-continent, tomato leaf curl disease (ToLCD) of tomato caused by begomoviruses has emerged as a major limiting factor for tomato cultivation. Despite the spread of this disease in the western India, a systematic study on the characterization of virus complexes with ToLCD is lacking. Here, we report the identification of a complex of begomoviruses including 19 DNA-A and 4 DNA-B as well as 15 betasatellites with ToLCD in the western part of the country. Additionally, a novel betasatellite and an alphasatellite were also identified. The recombination breakpoints were detected in the cloned begomoviruses and betasatellites. The cloned infectious DNA constructs cause disease on the tomato (a moderately virus-resistant cultivar) plants, thus fulfilling Koch's postulates for these virus complexes. Further, the role of non-cognate DNA B/betasatellite with ToLCD-associated begomoviruses on disease development was demonstrated. It also emphasizes the evolutionary potential of these virus complexes in breaking disease resistance and plausible expansion of its host range. This necessitates to investigate the mechanism of the interaction between resistance breaking virus complexes and the infected host.

Breeding tomatoes suitable for processing with triple disease resistance to tomato leaf curl disease, bacterial wilt and early blight

India is the second largest producer of tomato with 11 per cent global share and cultivated on an estimated area of 0.76 million hectares with productivity of 24 tonnes per hectare. Less than 1% of the produce is processed when compared to 26% in other major producing countries. Of the estimated more than 41 million tonnes of tomato processed globally, only 130,000 tonnes were processed in India and domestic demand for processed tomato products is expanding at an estimated 30% annually. At present traditional fresh market tomato cultivars are being processed though such cultivars are unsuitable for processing. Processors in India are looking for high yielding tomato cultivars with high total soluble solids (5-6 º Brix), acidity not less than 0.4%, pH less than 4.5 and uniform red colour with a/b colour value of at least 2. In addition, firm fruited tomato cultivars with joint less pedicel (j2) which facilitate mechanical harvesting or rapid hand picking. ICAR-Indian Institute of Horticultural Research has recently developed two high yielding F1 hybrids in tomato viz: Arka Apeksha and Arka Vishesh suitable for processing. On evaluation for three years, both the hybrids recorded good level of total soluble solids (4.5-5º Brix) and colour value of 2. Further, both the hybrids had high yield potential (80-90 tonnes / hectare) with triple disease resistance to tomato leaf curl disease, bacterial wilt and early blight. Arka Apeksha and Arka Vishesh were also bred with jointless pedicel making them suitable for mechanical harvesting. Our experimental studies on vine storability revealed that all the fruits were intact on plants even 110 days after transplanting in the main field facilitating once over harvest.

Physiological and transcriptomic analyses revealed gene networks involved in heightened resistance against tomato yellow leaf curl virus infection in salicylic acid and jasmonic acid treated tomato plants.

Tomato yellow leaf curl virus (TYLCV), a member of the genus Begomovirus of the Geminiviridae family, causes leaf curl disease of tomato that significantly affects tomato production worldwide. SA (salicylic acid), JA (jasmonic acid) or the JA mimetic, COR (coronatine) applied exogenously resulted in improved tomato resistance against TYLCV infection. When compared to mock treated tomato leaves, pretreatment with the three compounds followed by TYCLV stem infiltration also caused a greater accumulation of H2O2. We employed RNA-Seq (RNA sequencing) to identify DEGs (differentially expressed genes) induced by SA, JA, COR pre-treatments after Agro-inoculation of TYLCV in tomato. To obtain functional information on these DEGs, we annotated genes using gene ontology (GO) and Kyoto encyclopedia of genes and genomes (KEGG) databases. Based on our comparative analysis, differentially expressed genes related to cell wall metabolism, hormone signaling and secondary metabolism pathways were analyzed in compound treated samples. We also found that TYLCV levels were affected in SlNPR1 and SlCOI1 silenced plants. Interestingly, compared to the mock treated samples, SA signaling was hyper-activated in SlCOI1 silenced plants which resulted in a significant reduction in viral titer, whereas in SINPR1 silencing tomato plants, there was a 19-fold increase in viral load. Our results indicated that SA, JA, and COR had multiple impacts on defense modulation at the early stage of TYLCV infection. These results will help us better understand SA and JA induced defenses against viral invasion and provide a theoretical basis for breeding viral resistance into commercial tomato accessions.

Disruption of tomato TGS machinery by ToLCNDV causes reprogramming of vascular tissue-specific TORNADO1 gene expression.

Vascular development-related TRN1 transcription is suppressed by cytosine methylation in fully developed leaves of tomato. ToLCNDV infection disrupts methylation machinery and reactivates TRN1 expression - likely causing abnormal leaf growth pattern. Leaf curl disease of tomato caused by tomato leaf curl New Delhi virus (ToLCNDV) inflicts huge economical loss. Disease symptoms resemble leaf developmental defects including abnormal vein architecture. Leaf vein patterning-relatedTORNADO1gene's (SlTRN1) transcript level is augmented in virus-infected leaves. To elucidate the molecular mechanism of the upregulation ofSlTRN1in vivo, we have deployedSlTRN1promoter-reporter transgenic tomato plants and investigated the gene's dynamic expression pattern in leaf growth stages and infection. Expression of the gene was delimited in the vascular tissues and suppressed in fully developed leaves. WRKY16 transcription factor readily activated SlTRN1 promoter in varied sized leaves and upon virus infection, while silencing of WRKY16 gene resulted in dampened promoter activity. Methylation-sensitive PCR analyses confirmed the accumulation of CHH methylation at multiple locations in theSlTRN1promoter in older leaves. However, ToLCNDV infection reverses the methylation status and restores expression level in the leaf vascular bundle. The virus dampens the level of key maintenance and de novo DNA methyltransferases SlDRM5, SlMET1, SlCMT2 with concomitant augmentation of two DNA demethylases, SlDML1 and SlDML2 levels inSlTRN1promoter-reporter transgenics. Transient overexpression of SlDML2 mimics the virus-induced hypomethylation state of theSlTRN1promoter in mature leaves, while silencing of SlDML2 lessens promoter activity. Furthermore, in line with the previous studies, we confirm the crucial role of viral suppressors of RNA silencing AC2 and AC4 proteins in promoting DNA demethylation and directing it to restore activated transcription ofSlTRN1. Unusually elevated expression of SlTRN1 may negatively impact normal growth of leaves.

Tomato Leaf Curl Disease: A Review

Tomato is a most economic vegetable in India. Covers major area in its cultivation during crop production, it is threatened by major viral disease i.e tomato leaf curl disease, caused by begomovirus and transmitted by the vector. It causes yield loss up to 90-100 per cent, application of insecticide for the control of vector causes regular outbreak. Identification of resistant source from wild species and their introgression with susceptible source, development of lines/varieties, resistant/tolerant to Tomato leaf curl disease is the safest and long term alternative for solving this problem. This paper covers the major aspect related to virus, virus causing factors, vectors and sources of disease resistance and also breeding tools employed for its resistance and some of the barriers in breeding programme.

First complete genome sequence of Tomato leaf curl virus (ToLCV) from Salvia splendens in India

AbstractThe complete genome sequences of a Begomovirus and associated betasatellite were obtained by the rolling circle amplification method from a symptomatic Salvia (Salvia splendens) plant showing severe leaf curling, leaf deforming and yellowing, from Gorakhpur, Uttar Pradesh, India. The viral genome (DNA‐A) sequence showed the highest nucleotide identity (99.75%) with an isolate of Tomato Leaf Curl Virus (ToLCV), whereas the associated satellite sequence exhibited the highest nucleotide similarity of 98.47% with the isolate of Chilli leaf curl betasatellite (ChiLCB). The virus present in the infected salvia plant was successfully transmitted by whitefly to healthy salvia and tomato. The phylogenetic analysis reveals that although the ToLCV is segregated by the host but closely related to the isolate originating from India, whereas the same is found with the associated betasatellite. The study finds that evolutionary analysis along with recombination value solely cannot explain its relative frequency. Somehow, mutation, and nucleotide substitution, contributed to the evolution and diversification of this ToLCV together with the co‐adaptation of its betasatellite. However, ToLCV was found to have more diverse recombination events as compared with betasatellite. Consequently, the low frequency of polymorphism suggests a background selection or recent expansion occurring in populations of Begomoviruses. In addition, haplotype diversity (Hd) was detected as equal to 1 for ToLCV and very close to 1 for ChiLCB, signifying the uniqueness of the isolate. Our result indicates that S. splendens plants infected with ToLCV coupled with betasatellite act as an alternative host and that could lead to an increased incidence and emergence of new variants of tomato leaf curl diseases. To our knowledge, this is the first report of ToLCV and its associated betasatellite infecting Salvia in India. This study based on different evolutionary indices may provide insight into the future evolutionary study of different species of Begomoviruses.

Scenario of Early Blight and Leaf Curl of Tomato in Gwalior Districts of Madhya Pradesh

Alternaria solani fruit rot of tomato. Among them, early blight is the most destructive. Present investigations were undertaken to study the disease incidence of early blight in Gwalior districts, which ranged from 12.50 to 51.30%. Maximum disease incidence was recorded in Shyawari (51.30%), while minimum incidence was recorded in Duhiya (12.50%). The leaf curl disease of tomato ranged from 15.33 to 63.20% and maximum disease incidence of tomato leaf curl disease on tomato recorded in Ganpatpura (63.20%) while minimum disease incidence was recorded in Birampura (15.33%).

Molecular analysis, infectivity and host range of Tomato leaf curl Karnataka virus associated with Corchorus yellow vein mosaic betasatellite

Severe leaf curl disease of tomato (ToLCD) was noticed recently in the central parts of India and is an emerging threat to the cultivation of tomato. The genomic components of the begomovirus isolate, DNA A and betasatellite associated with ToLCD were cloned by rolling circle amplification method and sequenced. The sequence analysis revealed that the DNA A (2766 nt) of this isolate had the nucleotide identity of >91% with other strains of Tomato leaf curl Karnataka virus (ToLCKV), hence this isolate is proposed as a strain of ToLCKV, named as ToLCKV-Raipur. Similarly, the betasatellite molecule (1355 nt) had the highest identity of 91.1% with Corchorus yellow vein mosaic betasatellite (CoYVMB) and named as CoYVMB-Raipur. The full-length dimerized clones of these two genomic components were agroinoculated on natural (tomato), experimental (Nicotiana benthamiana) hosts and other 20 plant species belong to six different families. The severe leaf curl symptoms appeared only in the hosts, N. benthamiana, and in tomato inoculated with ToLCKV-Raipur alone and ToLCKV-Raipur with CoYVMB-Raipur after 8 and 16-18 days inoculation, respectively. This isolate was also transmissible to healthy tomato plants by whitefly from the tomato plant agroinoculated with ToLCKV-Raipur alone and with CoYVMB-Raipur and produced symptoms within 14-16 days after inoculation. Interestingly, this isolate infects horse gram and chilli by whitefly transmission and both the hosts showed positive for DNA A alone but not for betasatellite. Quantification of the genomic components of this isolate with the agroinoculated N. benthamiana samples by qRT-PCR results showed that the quantity of ToLCKV-Raipur was enhanced by three-fold while inoculated with CoYVMB-Raipur compared to ToLCKV-Raipur alone inoculated plants. However, CoYVMB-Raipur did not enhance the levels of ToLCKV-Raipur in the agroinoculated tomato plants. This is the first evidence of the natural co-occurrence of ToLCKV with betasatellite, CoYVMB causing ToLCD.

Evaluation of tomato genotypes for resistance to whitefly (Bemisia tabaci Gennadius) and tomato leaf curl virus in eastern India

Tomato production in the tropics is threatened by whitefly infestation and tomato leaf curl virus (ToLCV) causing severe economic losses. No stable resistance to these biotic challenges has been identified in eastern India. Therefore, initial screening of 19 advance breeding lines of tomato was carried out during the year 2016–17. Based on the whitefly population per leaf and tomato leaf curl disease severity, eight tomato genotypes were selected for final screening during the year 2017–18. Morphological leaf traits and biochemical parameters in tomato leaf were assessed in selected genotypes and considered as potential mediators of resistance. Significant variation was observed for whitefly infestation and ToLCV disease severity among the tomato genotypes tested. Higher leaf trichome density with narrow and thinner leaves and higher total phenol content in leaf emerged as reliable morphological and biochemical markers for early selection of tomato genotype resistant to whitefly and ToLCV disease. The resistance of tomato genotypes 2016/Res-1, 2015/Res-5, 2014/Res-1 and 2014/Res-4 to both whitefly and ToLCV disease is based on antixenotic properties and they could be utilized in future breeding to enhance stable resistance against these biotic challenges.

Tomato leaf curl Oman virus and associated Betasatellite causing leaf curl disease in tomato in Pakistan

The ongoing global spread of Tomato yellow leaf curl virus (TYLCV) poses an endemic threat to tomato production in all tropical and sub-tropical regions of the world. In Oman, TYLCV evolved into the new species Tomato leaf curl Oman virus (ToLCOMV) by recombination with Papaya leaf curl virus (PaLCuV). In March 2017, during a field survey of Sindh province of Pakistan, tomato (Solanum lycopersicum L.) plants showing typical symptoms of Tomato leaf curl disease (ToLCD); such as leaf curling, yellowing and stunted plant growth were observed. For identification and characterization of the causative agent, leaf samples were collected and tested for the presence of begomoviruses and associated DNA satellites. We have recently reported the presence of ToLCOMV-PK (previously known as TYLCV-PK strain) on Cyamopsis tetragonoloba in the same province of Pakistan. The tomato samples were analyzed for the presence of ToLCOMV-PK using specific primers. Approx. 2.8 kb and 1.4 kb PCR products were obtained which were cloned and sequenced; the results indicated the presence of ToLCOMV-PK and Tomato leaf curl betasatellite (ToLCB). We were also able to identify defective molecules of ToLCOMV-PK which were about half the size of the complete virus. Phylogenetic analysis and the sequence demarcation tool (SDT) showed that these are new isolates of ToLCOMV-PK (ToLCOMV-Pakistan strain) associated with ToLCB. Recombination analysis detected a strong recombination event in ToLCOMV-PK in which TYLCV (JQ928346) and PaLCuV (LT009400) were major and minor parents, respectively. We also corrected the classification of the previously identified distinct strain i.e. TYLCV-PK (TYLCV-Pakistan strain) into ToLCOMV-PK strain, based on our current analysis and classification. Biolistic inoculation of ToLCOMV-PK and associated ToLCB in Nicotiana benthamiana plants showed that coinfection with ToLCB resulted in enhanced symptoms and virus accumulation. This report of ToLCOMV-PK associated with ToLCB infecting tomato in Pakistan represents the widespread and vast host range of ToLCOMV and which poses serious threat to tomato production in Pakistan.

Begomoviruses affecting pulse and vegetable crops are unevenly distributed in distinct agroecological zones of the eastern India

AbstractIntensive cultivation, climate change and host–pathogen dynamics/interaction had led to emergence of viral diseases and vector population, thereby causing significant economic losses. In the present study, extensive surveys were conducted (during 2016–2017) followed with field experiments (2017 and 2019 kharif and 2018 rabi seasons) in the state of Chhattisgarh, India, comprising of three diverse agroecological zones, viz., northern hill zone, central plain zone and southern Bastar plateau zone, for understanding the distribution pattern of viruses and vector populations in prominent pulses and vegetable crops. Field experiments revealed that more than 90% incidence of yellow mosaic disease (YMD) was recorded in mungbean and urdbean, followed by YMD of ridge gourd and bitter gourd, leaf curl disease of tomato (ToLCD) and chilli and yellow vein mosaic disease of bhendi; however, only five per cent YMD was recorded in cow pea. Molecular and sequence analysis of viral genomic components revealed ToLCD in central plain zone of Chhattisgarh was caused by a consortium of begomoviruses, including Tomato leaf curl New Delhi virus (ToLCNDV), Tomato leaf curl Karnataka virus (ToLCKV), and Tomato leaf curl Kerala virus associated with satellite molecules. YMD of mungbean, cow pea and soybean was caused by Mungbean yellow mosaic India virus (MYMIV), while YMD of ridge gourd was caused by ToLCNDV. PCR analysis, using species‐specific primers, of samples representing the three different regions revealed that YMD of mungbean, urdbean and cowpea was positive only for MYMIV and was unevenly distributed, while YMD of ridge gourd, bitter gourd, pumpkin and sponge gourd was positive only for ToLCNDV; however, ToLCD was positive for either ToLCNDV or ToLCKV or both, and some samples were also found associated with betasatellite molecules. Amaranthus and rice bean were identified as non‐host species for the begomoviruses infecting tomato and MYMIV, as observed by surveys in the hot‐spot‐like areas, controlled whitefly transmission as well as agroinoculation. Compilation and analysis of available information on begomoviruses affecting these crops in India suggest that they are unevenly distributed in India. This is the first report of the begomovirus occurrence in pulses and vegetable crops in this agroecologically diverse region.

Two distinct monopartite begomovirus-betasatellite complexes in western India cause tomato leaf curl disease

In India, begomovirus infection causing tomato leaf curl disease (ToLCD) is a major constraint for tomato productivity. Here, we have identified two distinct monopartite begomovirus and betasatellite complexes causing ToLCD in the western part of India. A new monopartite begomovirus (Tomato leaf curl Mumbai virus, ToLCMumV) and betasatellite (Tomato leaf curl Mumbai betasatellite, ToLCMumB) were isolated from the Mumbai sample. A distinct Tomato leaf curl Gandhinagar virus (ToLCGanV) and Tomato leaf curl Gandhinagar betasatellite (ToLCGanB) were identified from the Gandhinagar sample. Both of the cloned begomoviruses were recombinants. The demonstration of systemic infection caused by begomovirus (ToLCGanV or ToLCMumV) alone in N. benthamiana and tomato (a virus resistant variety) emphasizes that they were monopartite begomoviruses. Co-inoculation of cognate begomovirus and betasatellite reduces the incubation period and increases symptom severity. Thus, Koch’s postulates were satisfied for these virus complexes. Further, an enhanced accumulation of ToLCGanV was detected in the presence of cognate ToLCGanB, however ToLCMumB did not influence the level of ToLCMumV in the agro-inoculated tomato plants. Our results indicate that the cloned viruses form potential virus resistance breaking disease complexes in India. This necessitates to investigate the spread of these disease complexes to major tomato growing regions in the country.

Interaction of a tomato leaf curl New Delhi virus with a betasatellite enhances symptom severity in field-infected tomato plants

Two field-collected tomato plants, with severe and mild tomato leaf curl disease symptoms, were shown to be infected with tomato leaf curl New Delhi virus. The plant with severe symptoms was shown to additionally contain tobacco leaf curl betasatellite (TobLCuB). Inoculation of Nicotiana benthamiana plants with the cloned components showed the severe symptoms to be due to the presence of TobLCuB. A shorter latent period was associated with the presence of TobLCuB except in the presence of the DNA-A and DNA-B components of the severe type. The DNA-B component from the mild type also reduced the latent period, more so than the DNA-B from the severe type, except in the interaction with the DNA-A from the mild type. These differences in the effects of the virus components from the two isolates may possibly be due to mutations in the DNA-B from the severe type. The results show that betasatellites can enhance the virulence of bipartite begomoviruses, even for isolates that induce quite mild symptoms.

Role of viral suppressors governing asymmetric synergism between tomato-infecting begomoviruses.

Mixed viral infections are common in fields and frequently exacerbate disease severity via synergistic interactions among individual viral genomic components leading to major crop loss. Two predominant species of tomato-infecting begomoviruses, Tomato leaf curl New Delhi virus (ToLCNDV) and Tomato leaf curl Gujarat virus (ToLCGuV), are known to cause severe leaf curl disease of tomato in India. Previously, we have demonstrated asymmetric synergism between these two distinct begomovirus species during mixed infection in solanaceous hosts. In the present study, we have identified the underlying proteins that positively regulate asymmetric synergism and their effect on plant defense machinery. During co-infection, the AC2 and AV2 of ToLCGuV enhanced ToLCNDV DNA accumulation in Nicotiana benthamiana as well as in their natural host, tomato. Furthermore, we found that AC2 and AV2 of ToLCNDV and AV2 of ToLCGuV play a critical role in suppression of post transcriptional gene silencing (PTGS) machinery. Taken together, AC2 and AV2 encoded proteins of ToLCGuV are the crucial viral factors promoting asymmetric synergism with ToLCNDV. KEY POINTS: • Begomoviral suppressors play vital roles in viral synergism. • AC2 and AV2 of ToLCGuV asymmetrically enhance ToLCNDV accumulation. • AC2 and AV2 of ToLCNDV and ToLCGuV AV2 are major PTGS suppressors.

Metagenomic analyses and genetic diversity of Tomato leaf curl Arusha virus affecting tomato plants in Kenya

BackgroundTomato production is threatened worldwide by the occurrence of begomoviruses which are associated with tomato leaf curl diseases. There is little information on the molecular properties of tomato begomoviruses in Kenya, hence we investigated the population and genetic diversity of begomoviruses associated with tomato leaf curl in Kenya.MethodsTomato leaf samples with virus-like symptoms were obtained from farmers’ field across the country in 2018 and Illumina sequencing undertaken to determine the genetic diversity of associated begomoviruses. Additionally, the occurrence of selection pressure and recombinant isolates within the population were also evaluated.ResultsTwelve complete begomovirus genomes were obtained from our samples with an average coverage of 99.9%. The sequences showed 95.7–99.7% identity among each other and 95.9–98.9% similarities with a Tomato leaf curl virus Arusha virus (ToLCArV) isolate from Tanzania. Analysis of amino acid sequences showed the highest identities in the regions coding for the coat protein gene (98.5–100%) within the isolates, and 97.1–100% identity with the C4 gene of ToLCArV. Phylogenetic algorithms clustered all Kenyan isolates in the same clades with ToLCArV, thus confirming the isolates to be a variant of the virus. There was no evidence of recombination within our isolates. Estimation of selection pressure within the virus population revealed the occurrence of negative or purifying selection in five out of the six coding regions of the sequences.ConclusionsThe begomovirus associated with tomato leaf curl diseases of tomato in Kenya is a variant of ToLCArV, possibly originating from Tanzania. There is low genetic diversity within the virus population and this information is useful in the development of appropriate management strategies for the disease in the country.

Evaluation of IDM modules for tomato leaf curl disease management in Madhya Pradesh

Comparative suitability assessment field trials of fourdifferent IDM modules for the management of leaf curldisease of tomato were conducted at farmer’s field. The trialcites were located in Chorgarhi, Mankesher and Upani villageof district Sidhi, Madhya Pradesh. The trials were conductedduring 2014-15, 2015-16 and 2016-17 as On Farm Trial. Trendof results obtained during past three years of experimentationindicated that all the management modules tested were foundsuperior over predominant farmer’s practice (M1). Themodule M4 having tolerant variety, seed treatment withinsecticide, nursery raising in nylon net cages of 40 mesh,root dip of seedling with systemic insecticide Imidacloprid,as to enable nursery to be transplanted, remain uninfestableby white flies and thrips at least up to 2 weeks aftertransplanting. Further, initial roughing at 3 weeks aftertransplanting and two subsequent sprays of systemicinsecticide before flowering, at 25 and 45 DAT was foundeffective not only in reducing disease incidence butdecreased total number of white fly per plant as well. Thispackage of practice was also able to enhance tomato yieldwith favorable cost benefit ratio. Module 4 was followed bymodule T3, where most of the measures mentioned in module4 were followed except use of nylon net. Therefore, it is verymuch evident that the seed treatment with insecticide andseedling dip measures along with physical intervention todeploy nylon net to prevent assess of vectors to nurseriesinside the cage, hold the great promise to have an almostleaf curl free crop.