Protected Tomato Crops Research Articles

Predation by Nesidiocoris tenuis on Bemisia tabaci and injury to tomato

Tomato is the most important vegetable crop in Spain. The mirid bug Nesidiocoris tenuis (Reuter) commonly appears in large numbers in protected and open-air tomato crops where little or no broad-spectrum insecticides are used. Nesidiocoris tenuis is known to be a predator of whiteflies, thrips and several other pest species. However, it is also considered a pest because it can feed on tomato plants, causing necrotic rings on stems and flowers and punctures in fruits. Our objectives were to evaluate predation by N. tenuis on sweetpotato whitefly Bemisia tabaci Gennadius under greenhouse conditions and establish its relationship to N. tenuis feeding on tomato. Two different release rates of N. tenuis were compared with an untreated control (0, 1 and 4 N. tenuis plant−1) in cages of 8 m2. Significant reductions of greater than 90% of the whitefly population and correspondingly high numbers of N. tenuis were observed with both release rates. Regression analysis showed that necrotic rings on foliage caused by N. tenuis were best explained by the ratio of B. tabaci nymphs:N. tenuis as predicted by the equation y = 15.086x − 0.6359.

Effect of tomato deleafing on mirids, the natural predators of whiteflies

Sustainability in Mediterranean greenhouse agrosystems involves environmentally-friendly techniques based on biological and non-chemical methods. Deleafing is a common agricultural practice used to accelerate fruit ripening and facilitate farming methods. However, deleafing may have an impact on mirids, a natural predator used to control whiteflies, which are considered among the most noxious insect pests of field and greenhouse crops worldwide. Here we studied the impact of leaf removal on populations of mirids. Two deleafing practices were tested: (a) regular deleafing, with the first removal of 2 leaves per plant 10 weeks after sowing; and (b) delayed deleafing, in which the first removal was delayed by 14 days. Our results show that regular deleafing had a strong negative impact on mirid populations. Indeed, the first deleafing of the regular method eliminated 74% of young nymphs. Such a loss was not observed with the delayed method because nymphs were older and already distributed on leaves which were never thinned. As a consequence of this initial difference, mirid populations were 60% higher in the delayed than in the regular deleafing treatments at the end of the crop. The biological control of whiteflies was less efficient in the regular deleafing crop for which densities were, on average, 30% higher than in the delayed deleafing crop. Such inefficiency could call into question the sustainability in protected tomato crops of environmentally-friendly techniques focused on reducing the pesticides used.

First Report of Tomato chlorosis virus and Tomato infectious chlorosis virus in Tomato Crops in France.

Since 2002, yellowing symptoms associated with high levels of white-fly populations have been observed in plants of protected tomato crops in France. Symptomatic plants exhibited interveinal yellowing areas in older leaves, followed by generalized yellowing. Symptoms were not observed in young plants or fruits. Trialeurodes vaporariorum populations were generally abundant in spring, and Bemisia tabaci (established in France for approximately 10 years) became predominant in summer and fall. To check for the presence of Tomato chlorosis virus (ToCV) and Tomato infectious chlorosis virus (TICV), two whitefly-transmitted criniviruses known to induce yellowing symptoms, 696 samples were collected in the major tomato-growing areas; 573 samples from southern France and 123 samples from northern France. Total RNA was extracted from each sample and analyzed using reverse transcription-polymerase chain reaction (RT-PCR). Primers specific to ToCV (2) and TICV (1,3) were used to amplify either part of the heat-shock-like protein gene HSP70h (both viruses) or part of the diverged coat protein gene (CPd), (TICV only). A 439-bp DNA fragment was obtained with ToCV primers in 178 samples from southern France collected mainly from mid-spring to early fall from 2002 to 2004. Three RT-PCR products amplified from samples collected from diverse growing areas were sequenced and showed 99 to 100% sequence identity with published ToCV sequences from Spain (GenBank Accession Nos. AF215818, AF233435, and AF215817), Portugal (GenBank Accession No. AF234029), Sicily (GenBank Accession No. AY048854), and the United States (GenBank Accession No. AF024630). Considering the high frequency of ToCV-infected samples (41 positive samples of 112 samples collected in 2002, 71 of 295 collected in 2003, and 66 of 166 collected in 2004), this virus appears to be well established in southern France but remains absent in the northern regions. The presence of TICV was tested in 485 samples using the CPd-specific primers or the HSP70h-specific primers. The virus was detected in only two samples from Nice (southeastern France) in 2003 with both primer pairs. The CPd DNA fragment (700 bp) from one of these samples was sequenced, showing 98.9% sequence identity with a TICV Japanese isolate (AB085603). Results of these assays suggest that in contrast to ToCV, TICV is not yet broadly established in France. This difference could be associated with the specificity of the vectors, since ToCV is transmitted by B. tabaci and T. vaporariorum, while TICV is transmitted only by T. vaporariorum (4).

Association of Pepino mosaic virus with Tomato Collapse

AbstractSince 1998 collapse of tomato plants has been producing significant losses in protected tomato crops along the Spanish Mediterranean coast. Affected plants show sudden and progressive wilt followed by total collapse and death. Analysis of the distribution and accumulation of Pepino mosaic virus (PepMV) in collapsed and non‐collapsed plants and the presence of the virus in all analysed collapsed plants suggests a relationship of this Potexvirus with tomato collapse. The fact that collapse does not occur on PepMV‐free farms reinforces this hypothesis. PepMV‐infected plants showed a necrotic area in the vascular system, mainly in the basal area of the stem. This necrosis was more pronounced in collapsed plants and in the areas with higher viral concentration. Our hypothesis is that tomato collapse would be associated with necrosis of the vascular system caused by PepMV accumulation.

Identification and characterization of Pepino mosaic potexvirus in tomato

At the beginning of 1999, a new virus disease occurred in protected tomato crops in The Netherlands. Initial diagnostic tests revealed the presence of a potexvirus but serological tests ruled out the presence of Potato X potexvirus (PVX). Tests for other potexviruses reported from solanaceous crops provisionally identified the virus as Pepino mosaic potexvirus (PepMV). The virus was purified, and an antiserum was produced, which showed strong reactions with both the type isolate of PepMV from pepino and two other isolates from tomato. Host range and symptomatology of the pepino and tomato isolates of PepMV revealed clear differences from PVX. However, differences were also observed between the pepino and tomato isolates of PepMV. Sequence alignment of DNA fragments of 584 bp derived from the RNA polymerase cistron showed almost 95% identity with the pepino isolate, whereas the identity with PVX appeared to be < 60%. Together, these results identified PepMV as the causal agent of the new virus disease in tomato. Based on the differences from the type isolate from pepino (Solanum muricatum), the isolates from tomato should be considered as a distinct strain of PepMV for which the name tomato strain is proposed.

Control of the Bemisia tabaci/Tomato yellow leaf curl virus complex on protected tomato crops in Algarve (Portugal)*

The whitefly Bemisia tabaci has been a serious pest in protected tomato crops since 1995 in the south of Portugal (Algarve), causing severe losses mainly resulting from Tomato yellow leaf curl virus (TYLCV), first reported in the autumn/winter season. In order to manage and control the B. tabaci/TYLCV complex, experimental field trials were carried out between 1997 and 2000. Several control methods were tested, such as the application of white screen nets to windows and doors, chemical treatments against B. tabaci and the use of cucumber as a trap crop. The results show that the percentage of plants with TYLCV symptoms mainly reflects B. tabaci infestation level in the first 6 weeks. Screen net protection was the control method that clearly provided a low incidence of plants with TYLCV symptoms in the autumn/winter season. Additionally, insecticide treatments, made weekly in the first 6 weeks, may give improved protection. In the winter/spring season, the B. tabaci/TYLCV complex is a minor problem because of the low populations of B. tabaci and the climatic conditions. Information about the work in progress and results was given to growers through visits to the experimental fields and oral presentations.

Control of the Bemisia tabaci/Tomato yellow leaf curl virus complex on protected tomato crops in Algarve (Portugal)*

Control of the Bemisia tabaci/Tomato yellow leaf curl virus complex on protected tomato crops in Algarve (Portugal)*

First Report of Pepino mosaic virus on Tomato in Spain.

At the beginning of 2000, a damaging disease developed on protected tomato (Lycopersicon esculentum) crops grown in polyethylene greenhouses in different regions of Spain. Production losses were estimated at 15 to 80%. The tomato plants showed a variety of symptoms. The most common symptoms were leaf distortion, chlorosis, and mosaic. Some plants showed a dark green mosaic and bubbling of the leaf surface. Green striations were also observed on the stem and sepals. Most of the diseased plants had discolored fruits. Symptoms decreased as environmental temperature increased. The involvement of Pepino mosaic virus (PepMV) was suspected. To identify the etiological agent, ≈500 symptomatic tomato plants were collected from several locations in Alicante, Murcia, Almeria and the Canary Islands. Flexuous viral particles 510 nm long were observed by transmission electron microscopy, suggesting the presence of a potexvirus in the tissue extracts analyzed. All samples were tested by ELISA (enzyme-linked immunosorbent assay), using polyclonal antibodies to Narcissus mosaic virus (Adgen, Auchincriuve, Scotland), a virus serologically related to PepMV, and two antisera specific to PepMV (Adgen, Scotland and DMSZ, Braunschweig, Germany). PepMV was detected in 35% of the samples. Like PepMV, the virus infected (as confirmed by ELISA) greenhouse-grown Datura stramonium, Nicandra physalodes, Nicotiana benthamiana, N. clevelandii, Solanum tuberosum, and Vigna sinensis and did not infect Capsicum anuum, Cucumis sativus, Chenopodium amaranticolor, C. quinoa, Petunia × hybrida, Phaseolus vulgaris, Physalis floridana, N. glutinosa, N. rustica, or N. tabacum. The virus did infect Gomphrena globosa, which normally is not infected by PepMV. The first report of PepMV was on pepino (Solanum muricatum) in Peru in 1974 (1), but this virus has been recently reported in the Netherlands, England, Germany, and France on protected tomato crops (2). To our knowledge, this is the first report of PepMV in Spain, including the Canary Islands.

First Report of Pepino mosaic virus on Natural Hosts.

Pepino mosaic virus (PepMV) is a potexvirus recently identified as the causal agent of a new disease occurring in protected tomato (Lycopersicon esculentum Mill.) crops in the Netherlands (2). PepMV has been subsequently identified in England, Germany, Italy, Morocco, Portugal, and Spain. The new disease has become a serious problem for tomato production in Europe. Most infected tomato plants expressed leaf distortion, chlorosis, and yellow mosaic. Other plants expressed mosaic and bubbling of the leaf surface. Tomato fruits showing severe discoloration and mosaic were observed in protected tomato crops. Symptoms attenuated in tomato plants as the ambient temperature increased. At present, only Solanum muricatum Ait. (Peruvian pepino) and L. esculentum are affected by PepMV.To determine possible reservoir hosts for this virus, 70 samples from Amaranthus sp., A. viridis (L.) Britton et al., Chenopodium murale L., Convolvulus arvensis L., Malva parviflora L., Nicotiana glauca Grah., Polypogon monspeliensis (L.) Desf., Senecio vulgaris L., Sisybrium sp., Solanum nigrum L., and Sonchus oleraceus L. were analyzed. The plants were collected around greenhouses affected by PepMV from different regions in Spain (Murcia and Canary Islands). The samples were analyzed for PepMV by double-antibody sandwich enzyme-linked immunosorbent assay with a commercial antiserum (DSMZ AS-0554, Biologische Bundesantstal, Braunschweig, Germany). Only Amaranthus sp., M. parviflora, N. glauca, Solanum nigrum, and Sonchus oleraceus tested postive. The presence of PepMV in these weed species was confirmed by electron microscopy and reverse transcription-polymerase chain reaction using degenerate primers for potexvirus (1). All the hosts analyzed were asymptomatic. However, symptoms were reproduced by mechanically inoculating tomato plants with sap from naturally infected weeds. To our knowledge, this is the first report of natural infection of weeds by PepMV.

Pathogenesis and control of bacterial speck, Pseudomonas syringae pv. tomato, on tomato

Bacterial speck of tomato, caused by Pseudomonas syringae pv. tomato, was observed to cause severe symptoms, especially on protected tomato crops, during the winter season in the coastal area of Lebanon. This study was conducted to investigate the aetiology and pathogenesis of the bacterium involved and the efficacy of different chemicals for the control of the disease. Biochemical, physiological and pathological tests verified the identity of the bacterium involved as P. s. tomato. Periodic histological sectioning of inoculated tomato leaves showed that bacterial cells resided and multiplied in depressions and around trichome bases for 24 h before penetration through stomata and trichome basal cells. The bacteria invaded intercellular spaces and caused cell lignification, collapse and shrinkage, 48 h after inoculation. Necrotic lesions filled with bacterial masses and collapsed lignified cells were readily observable at and after 72 h. No detectable histological changes were observed in the yellow halo region surrounding the necrotic leaf specks. A thermostable toxin was produced by the pathogen and is involved in chlorotic symptom expression. An antibiotic mixture of streptomycin + oxytetracy-cline was most effective in controlling infections followed by copper oxychloride + mancozeb, tribasic copper sulphate + sulphur, copper oxychloride and copper oxychloride + zineb.

First Report of Pepino Mosaic Virus on Tomato.

Early in 1999 a new viral disease occurred in protected tomato (Lycopersicon esculentum) crops in the Netherlands. Infected plants showed yellow leaf spots and mosaic. Transmission electron microscopic analysis revealed particles typical of potexviruses. Only three potexviruses have been reported to infect solanaceous crops: Pepino mosaic virus (PepMV), Potato aucuba mosaic virus (PAMV), and Potato virus X (PVX). Inoculation of test plants and serological tests showed that the new virus clearly differed from PAMV and PVX. Immuno-electron microscopy with antiserum to PepMV (1), the original PepMV isolate, and the virus from tomato showed decoration titers of 1:800 (homologous) and 1:400, respectively. Neither virus reacted with antiserum to PVX, nor did PVX react with antiserum to PepMV. Results of host plant analysis with 17 plant species mostly resembled those expected for PepMV. Nucleotide sequence alignment of DNA fragments obtained by reverse-transcriptase polymerase chain reaction with a specific primer set for potexviruses, directed against the RNA polymerase region, showed 93% identity between PepMV and the virus from tomato, while homologies with PVX, PAMV, and other potexviruses were <60%. Results indicate that the potexvirus in tomato is PepMV. PepMV was first found in pepino (Solanum muricatum) in Peru in 1974 and described by Jones et al. in 1980 (1). This is the first report of a natural infection of tomato by PepMV. Reference: (1) R. Jones et al. Ann. Appl. Biol. 94:61, 1980.

First Report of Tomato Yellow Leaf Curl Virus in Réunion Island.

In September 1997, stunting, reduced leaf size, leaf curling, and yellow margins were observed on tomato plants on a farm on the south coast of Réunion, a French island belonging to the Mascarenes archipelago. To our knowledge, these symptoms appeared to be characteristic of a tomato yellow leaf curl virus (TYLCV) infection. Diseased plants gave positive reactions with a triple antibody sandwich-enzyme-linked immunosorbent assay (TAS-ELISA), using ADGEN antibodies specific for begomoviruses (1). The serological results were confirmed by polymerase chain reaction (PCR) with a pair of degenerate primers-MP16, 5'-CCTCTAGATAATATTAC(C/T)(G/T)(G/A)(A/T)(T/G)G(G/A)CC-3' and MP82, 5'-CGGAATTC(T/C)TGNAC(C/T)TT(G/A)CANGGNCC(T/C)T C(G/A)CA-3'-designed by Malla Padidam (ILTAB, San Diego, CA) to amplify a region of the A component of begomoviruses, between the intergenic conserved nonanucleotide sequence (TAATATTAC) and the first 5' quarter of the capsid protein gene. A 500-bp PCR product was obtained from a symptomatic plant but not from a healthy looking one. After cloning the PCR product in a pGEM-T Easy vector (Promega, Madison, WI) and sequencing it with plasmid-specific primers (SP6, T7), the sequence was compared with the sequences of the NCBI data base, with the use of BLAST. Nineteen sequences among those producing the highest scoring segment pairs were compared with each other and with the 500-bp PCR product from Réunion by the Clustal method of MegAlign (DNASTAR, London). The Réunion sequence (AJ010790) was at least 94% similar to sequences of TYLCV isolates from the Dominican Republic (AF024715), Cuba (AJ223505), and Israel (X15656, X76319 for the mild clone). Based on these results, it appeared that the analyzed tomato plant was infected by a geminivirus isolate belonging to the Israeli species of TYLCV. A preliminary survey was carried out from December 1997 to April 1998 in both outdoor and protected tomato crops. Infected plants were detected by TAS-ELISA in 52 of the 123 locations visited. Severe economic losses were observed: 14 locations with 60 to 100% yield reduction and 11 locations with 40 to 60% yield reduction. All the infected samples were collected in the leeward coast, which is the driest region of the island. Although Bemisia tabaci (Gennadius) has been recorded since 1938 in Réunion (2), it has been observed on tomato crops only since 1997 and population levels were low compared with those of Trialeurodes vaporariorum Westwood. During the first six months of 1998, B. tabaci was found on Euphorbia heterophylla L., Lantana camara L., Solanum melongena L., S. nigrum L., and Phaseolus vulgaris L. These host plants often occur near infected tomato crops.