Tomato Leaf Surface Research Articles

Analysis of the Factors Affecting the Deposition Coverage of Air-Assisted Electrostatic Spray on Tomato Leaves

In order to investigate the effects of various factors (charging voltage, spray distance and spray pattern) on the deposition coverage of tomato leaves, the Box–Behnken surface response methodology was used to design an outdoor air-assisted electrostatic spraying experiment with three factors and three levels. The deposition coverage of tomato leaves in the upper, middle and lower layers was collected under different polarity charging voltages (0, +10 kV, −10 kV), spray distances (1, 3, 5 m) and spray patterns (ascending spray, descending spray, fixed height spray). Regression analysis and variance analysis were performed on the experimental data to determine the optimal working parameters. The results showed that (1) spray distance is the most important factor affecting the droplet coverage rate in the process of air-assisted electrostatic spraying; (2) the droplet coverage rate of air-assisted electrostatic spraying is optimal when the charging voltage polarity is negative voltage, the spray distance is 2.75 m, and the spray pattern is descending spray. The following conclusions were obtained. (1) In air-assisted electrostatic spraying, the distribution of air flow had the greatest effect on droplet deposition on tomato leaf surface. (2) Compared with air-assisted non-electrostatic spray, air-assisted electrostatic spray had a better deposition effect.

Harnessing Nanoencapsulated Bacillus spp. Consortia To Combat Groundnut Bud Necrosis Orthotospovirus in Tomato.

Tomato (Solanum lycopersicum L.), a globally significant vegetable crop, faces a substantial threat from viral diseases, specifically Groundnut bud necrosis orthotospovirus (GBNV). Traditional approaches such as removal of infected plants, use of barrier crops, and insecticides have been employed but they have not proven to be consistently effective. Consequently, an alternative approach involving the stimulation of host resistance through the Plant Growth Promoting Rhizobacteria (PGPR) was adopted. From the previous study, B. subtilis (BST8), B. subtilis (Bbv57), and B. amyloliquefaciens (Ka1) were found to be effective against GBNV in cowpea. To enhance the shelf life of Bacillus spp. and improve the water retention capacity of tomato leaf surfaces, these bacteria were encapsulated within nanosilica, an identified host defense inducer. An effective inverse Pickering emulsion with a 2.5% (w/v) silica concentration was developed and characterized using diverse techniques, viz., phase contrast, scanning electron microscopy, confocal microscopy, contact angle goniometry, and variable angle ellipsometry. The prepared emulsion was then tested for its antiviral efficacy against GBNV in cowpea and tomatoes. Nanoencapsulated Bacillus consortia significantly reduced GBNV lesions in cowpea to 0.63 per leaf compared to the control (6.63). DAC-ELISA revealed a virus titer of 0.75 (3.33 times lower than the control), indicating antiviral efficacy. In tomato (var. PKM1), the consortia achieved an impressive 77.91% disease reduction (19% DSI) at 14 days post-inoculation (DPI), surpassing both nanoemulsion and consortia alone (DSIs: 67 and 30%, respectively). Nanoencapsulated Bacillus consortia demonstrated the lowest GBNV titer in tomatoes (0.86 vs control-3.32) through DAC-ELISA. This study introduces a promising strategy for the effective management of GBNV in cowpea and tomatoes using nanoencapsulated Bacillus consortia, underscoring its potential as an effective solution in crop protection.

Effect of pesticide application on Salmonella survival on inoculated tomato leaves

AbstractOutbreaks of Salmonellosis have been traced to contaminated tomato. The produce production environment poses a risk for Salmonella contamination; however, little is known about the effects of pest management practices on Salmonella during production. The study objective was to evaluate pesticide application on the inactivation of Salmonella on tomato leaves. Thirty greenhouse‐grown tomato plants were inoculated with S. enterica serovars Newport or Typhimurium. Inoculation was performed by dipping tomato leaves in an 8‐log CFU/mL Salmonella suspension with 0.025% (vol/vol) Silwet L‐77 surfactant for 30 s, for a starting concentration of 6–7 log CFU/mL. Plants were treated with one of four pesticides, each with a different mode of action [acibenzolar‐S‐methyl, copper‐hydroxide, peroxyacetic acid (PAA), and streptomycin]. Pesticides were applied at manufacturers' labeled rate for plant disease management with water as a control treatment. Salmonella was enumerated at 0.125 (3 h), 2, 6, and 9 days post‐inoculation (dpi), and counts log‐transformed. Growth of Salmonella was not observed. At 2 dpi, PAA and streptomycin significantly reduced surface Salmonella concentrations of inoculated tomato leaves (0.7 and 0.6‐log CFU/g, respectively; p ≤ 0.05), while significant Salmonella log reduction occurred in the ground tomato leaves after copper hydroxide treatment (0.8‐log CFU/g; p ≤ 0.05), compared to the control. No significant differences in Salmonella populations on tomato leaf surface and in ground leaves were observed from 2 to 9 dpi, regardless of pesticide application. These findings suggest single in‐field pesticide applications may not be an effective mitigation strategy in limiting potential Salmonella contamination. Future research, including multiple in‐field pesticide applications, or pesticide use in combination with other mitigation strategies, may offer intriguing management practices to limit possible preharvest contamination.

Elucidating the effect of tomato leaf surface microstructure on Botrytis cinerea using synthetic systems.

For some pathogenic fungi, sensing surface topography is part of their infection strategy. Their directional growth and transformation to a new developmental stage is influenced by contact with topographic features, which is referred to as thigmo-response, the exact functionality of which is not fully understood. Research on thigmo-responses is often performed on biomimetically patterned surfaces (BPS). Polydimethylsiloxane (PDMS) is especially suitable for fabrication of BPS. Here, we used synthetic BPS surfaces, mimicking tomato leaf surface, made from PDMS with the pathogenic fungus Botrytis cinerea to study the influence of structural features of the leaf surface on the fungus behavior. As a control, a PDMS surface without microstructure was fabricated to maintain the same chemical properties. Pre-penetration processes of B. cinerea, including the distribution of conidia on the surface, germination, and germ tube growth were observed on both leaf-patterned and flat PDMS. Microstructure affected the location of immediate attachment of conidia. Additionally, the microstructure of the plant host stimulated the development of germ tube in B. cinerea, at a higher rate than that observed on flat surface, suggesting that microstructure plays a role in fungus attachment and development.

Effects of Leaf Surface Roughness and Contact Angle on In Vivo Measurement of Droplet Retention

Droplet retention during pesticide application is a serious problem because run-off droplets flow out of the target area and pose a hazard to human health and the environment. The present study was conducted with the aim to measure the droplet retention of sprayed droplets on crop leaves in vivo using a constructed test system. In the measurement, three crop species with different surface properties (tomato, chili pepper, and winter wheat) were selected for droplet retention determination, and the variations in the time intervals of maximum retention and stable retention were determined. Contact angle and surface roughness (Ra), which are the most important surface properties of crop leaves, were used as independent variables. The Ra values of tomato, pepper, and winter wheat were 24.73 μm, 5.28 μm, and 17.59 μm, respectively, while the contact angles of tomato, pepper, and winter wheat were 97.67°, 70.07° and 131.98°, respectively. The results showed that the curves of droplet retention on sprayed tomato and wheat leaves had similar patterns over time and could be divided into four periods (rapidly increasing period, slowly increasing period, collapsing period, and stable period). The maximum droplet retention on tomato leaf surface was Rmax = 0.169 g⋅cm−2, and the stable retention was Rst = 0.134 g⋅cm−2. The maximum droplet retention on the surface of winter wheat leaf was Rmax = 0.244 g⋅cm−2, and the stable retention was Rst = 0.093 g⋅cm−2. However, droplet retention on pepper leaves was different from that on tomato and wheat leaves. The curve pattern of droplet retention on pepper leaves over time showed two peaks and two valleys. Moreover, the maximum retention, Rmax, was in the range of 0.149~0.151 g⋅cm−2, and the stable retention was Rst = 0.077 g⋅cm−2. It is expected that the obtained results can be used to characterize the properties of crop leaves and that this study can contribute to the improvement of droplet retention for effective chemical application and the reduction in the environmental pollution caused by agricultural pesticides.

The Role of Surfactin Production by Bacillus velezensis on Colonization, Biofilm Formation on Tomato Root and Leaf Surfaces and Subsequent Protection (ISR) against Botrytis cinerea.

Many aspects regarding the role of lipopeptides (LPs) in bacterial interaction with plants are not clear yet. Of particular interest is the LP family of surfactin, immunogenic molecules involved in induced systemic resistance (ISR) and the bacterial colonization of plant surfaces. We hypothesize that the concentration of surfactin produced by a strain correlates directly with its ability to colonize and persist on different plant surfaces, which conditions its capacity to trigger ISR. We used two Bacillus velezensis strains (BBC023 and BBC047), whose antagonistic potential in vitro is practically identical, but not on plant surfaces. The surfactin production of BBC047 is 1/3 higher than that of BBC023. Population density and SEM images revealed stable biofilms of BBC047 on leaves and roots, activating ISR on both plant surfaces. Despite its lower surfactin production, strain BBC023 assembled stable biofilms on roots and activated ISR. However, on leaves only isolated, unstructured populations were observed, which could not activate ISR. Thus, the ability of a strain to effectively colonize a plant surface is not only determined through its production of surfactin. Multiple aspects, such as environmental stressors or compensation mechanisms may influence the process. Finally, the importance of surfactin lies in its impacts on biofilm formation and stable colonization, which finally enables its activity as an elicitor of ISR.

Role of Nanoscale Hydroxyapatite in Disease Suppression of Fusarium-Infected Tomato.

The present study investigated the mechanisms by which large- and small-sized nanoscale hydroxyapatite (nHA) suppressed Fusarium-induced wilt disease in tomato. Both nHA sizes at 9.3 mg/L (low) and 46.5 mg/L (high dose) phosphorus (P) were foliar-sprayed on Fusarium-infected tomato leaf surfaces three times. Diseased shoot mass was increased by 40% upon exposure to the low dose of large-sized nHA compared to disease controls. Exposure to both nHA sizes significantly elevated phenylalanine ammonialyase activity and total phenolic content in Fusarium-infected shoots by 30-80% and 40-68%, respectively. Shoot salicylic acid content was also increased by 10-45%, suggesting the potential relationship between antioxidant and phytohormone pathways in nHA-promoted defense against fungal infection. Exposure to the high dose of both nHA sizes increased the root P content by 27-46%. A constrained analysis of principal coordinates suggests that high dose of both nHA sizes significantly altered the fatty acid profile in diseased tomato. Particularly, the diseased root C18:3 content was increased by 28-31% in the large-sized nHA treatments, indicating that nHA remodeled the cell membrane as part of defense against Fusarium infection. Taken together, our findings demonstrate the important role of nHA in promoting disease suppression for the sustainable use of nHA in nanoenabled agriculture.

Rain induces temporary shifts in epiphytic bacterial communities of cucumber and tomato fruit

Understanding weather-related drivers of crop plant-microbiome relationships is important for food security and food safety in the face of a changing climate. Cucumber and tomato are commercially important commodities that are susceptible to plant disease and have been implicated in foodborne disease outbreaks. To investigate the influence of precipitation on plant-associated microbiomes, epiphytically associated bacterial communities of cucumber and tomato samples were profiled by 16 S rRNA gene sequencing (V1-V3) in the days surrounding two rain events over a 17-day period. Following rain, α (within-sample) diversity measured on cucumber and tomato fruit surfaces, but not tomato leaf surfaces, increased significantly and remained elevated for several days. Bacterial β (between-sample) diversity on cucumber and tomato fruit responded to precipitation. In the cucumber fruit surface (carpoplane), notable shifts in the families Xanthomonadaceae, Oxalobacteriaceae, Sphingobacteriaceae and Comamonadaceae were detected following precipitation. In the tomato carpoplane, shifts were detected in the families Enterobacteriaceae and Xanthomonadaceae following the first rain event, and in the Pseudomonadaceae and Oxalobacteriaceae following the second rain event. Few taxonomic shifts were detected in the tomato leaf surface (phylloplane). Exploring rain-induced shifts in plant microbiomes is highly relevant to crop protection, food safety and agroecology, and can aid in devising ways to enhance crop resilience to stresses and climate fluctuations.

Protein Elicitor PeBL1 of Brevibacillus laterosporus Enhances Resistance Against Myzus persicae in Tomato.

Myzus persicae, a destructive aphid of tomato usually managed by chemical pesticides, is responsible for huge annual losses in agriculture. In the current work, a protein elicitor, PeBL1, was investigated for its capacity to induce a defense response against M. persicae in tomato. Population growth rates of M. persicae (second and third generation) decreased with PeBL1 treatments as compared with controls. In a host selection assay, M. persicae showed preference for colonizing control plants as compared to tomato seedlings treated with PeBL1. Tomato leaves treated with PeBL1 gave rise to a hazardous surface environment for M. persicae due to formation of trichomes and wax. Jasmonic acid (JA), salicylic acid (SA), and ethylene (ET) showed significant accumulation in tomato seedlings treated by PeBL1. The following results showed that PeBL1 significantly modified the tomato leaf surface structure to reduce reproduction and deter colonization by M. persicae. Defense processes also included activation of JA, SA, and ET pathways. The study provides evidence for use of PeBL1 in the protection of tomato from M. persicae.

Relative Level of Bacteriophage Multiplication in vitro or in Phyllosphere May Not Predict in planta Efficacy for Controlling Bacterial Leaf Spot on Tomato Caused by Xanthomonas perforans.

Following analysis of eight phages under in vitro, growth chamber and greenhouse conditions with the bacterial spot of tomato pathogen Xanthomonas perforans, there was no correlation between disease control efficacy and in vitro phage multiplication, in vitro bacterial suppression, or in vivo phage multiplication in the presence of the host, but there was a low correlation between phage persistence on the leaf surface and disease control. Two of the 8 virulent phages (ΦXv3-21 and ΦXp06-02) were selected for in depth analysis with two X. perforans (Xp06-2-1 and Xp17-12) strains. In in vitro experiments, phage ΦXv3-21 was equally effective in infecting the two bacterial strains based on efficiency of plating (EOP). Phage ΦXp06-02, on the other hand, had a high EOP on strain Xp06-2-1 but a lower EOP on strain Xp17-12. In several growth chamber experiments, ΦXv3-21 was less effective than phage ΦXp06-02 in reducing disease caused by strain Xp06-2-1, but provided little or no disease control against strain Xp17-12. Interestingly, ΦXp06-02 could multiply to significantly higher levels on the tomato leaf surface than phage ΦXv3-21. The leaf surface appears to be important in terms of the ability of certain bacteriophages to multiply in the presence of the bacterial host. ΦXv3-21, when applied to grapefruit leaves in combination with a bacterial host, was unable to multiply to high levels, whereas on tomato leaflets the phage multiplied exponentially. One plausible explanation is that the leaf surface may be an important factor for attachment of certain phages to their bacterial host.

A preliminary investigation into Aureobasidium pullulans as a potential biocontrol agent against Phytophthora infestans of tomato

Two biological control agents (BCAs), Aureobasidium pullulans L1 and L8 strains, were evaluated for their efficacy against Phytophthora infestans, the casual agent of tomato late blight. Yeast strains were applied (108 CFU/mL) on tomato plants, grown under greenhouse conditions, 24h before or 16h after inoculation with P. infestans (1×104 sporangia/mL). The BCAs applied 24h before the pathogen inoculation were significantly more effective (43.9%) than those applied after pathogen inoculation. L8 reduced AUDPC more (60%) than L1 (37%), while both strains reduced the disease in a similar way (average 32.2%) in the post-inoculation treatment. Dynamic population assay revealed that L1 and L8 were able to survive and colonize the tomato leaf surface during the ten days of experiments. In vitro experiments showed that both strains enhanced plant defence response by increasing leaf β-1,3-glucanase activity (>30% than the control). BCAs also produced bioactive volatile and non-volatile metabolites able to inhibit pathogen colony growth and to cause morphological alterations of hyphae. Overall, volatile metabolites were more effective than non-volatiles in reducing pathogen growth. In addition, 2-phenyl, 1-butanol-3-methyl, 1-butanol-2-methyl and 1-propanol-2-methyl synthetic volatile compounds produced by both strains showed EC50 values for pathogen mycelial growth of 3.9µLL−1 on average. This study showed that L1 and L8 strains could be considered part of a control strategy against P. infestans on tomato.

Biocontrol activity of Bacillus against a GFP-marked Pseudomonas syringae pv. tomato on tomato phylloplane

We report the biocontrol activity of the endophytic bacteria Bacillus pumilus and Bacillus amyloliquefacies against the plant pathogenic bacterium Pseudomonas syringae pv. tomato strain NS4 transformed with the GFP expressing gene. P. s. pv. tomato strain NS4 was obtained from the transformation of P. s. pv. tomato wild-type strain NW with the plasmid pNKGFP containing GFP-cassette for chromo- somal integration. The GFP-marked strain was tested for hy- persensitivity and pathogenicity, as well as population studies onthephylloplane,todetermineitsepidemiologyandsurvival. In all of the bioassays strain NS4 presented similar character- istics to the wild-type, and was hence chosen as the model strain for these studies with antagonistic endophytic bacterial strains. In the biocontrol experiments, tomato plants were pre- inoculated with the endophytic bacteria 4 days prior to inocu- lation with P. s. pv. tomato strains. On the tomato phylloplane the P. s. pv. tomato (strains NW and NS4) populations were drastically reduced, and tomato leaves showed reduced num- bers of bacterial speck lesions, comparable to the standard chemical treatment copper oxychloride. Additionally, under epifluorescence microscopy, few GFP-tagged cells of strain NS4 were observed colonizing important niches on the tomato phylloplane. However, leaves untreated with the antagonists presented a large number of GFP-tagged cell aggregates. Our results demonstrated that endophytic bacteria can also act efficiently on the biocontrol of bacterial speck when applied as a foliar spray on the leaves. In addition, we highlighted the use of GFP-marked strain NS4 as a model system to study biocontrol agent and pathogen interactions, and growth and development of the pathogen on the tomato leaf surface.

Effect of copper deficiency and of water stress on the microstructure of tomato leaf surface

The reaction of tomato plants cv. Tukan F<sub>1</sub> to copper deficiency and to water stress was compared. Plants grown in copper deficiency and in conditions of water stress were significantly smaller than controls. They had also lower turgor. The epidermis cells of the upper side leaf in the plants growing in copper deficiency or water stress conditions were smaller than in control plants. However the stomata and trichomes number of leaves plants with copper or water deficiency grown were bigger in comparision with control. The pores of stomata were always larger in leaves of control plants than in other objects.

Soil-based systemic delivery and phyllosphere in vivo propagation of bacteriophages: Two possible strategies for improving bacteriophage persistence for plant disease control.

Soil-based root applications and attenuated bacterial strains were evaluated as means to enhance bacteriophage persistence on plants for bacterial disease control. In addition, the systemic nature of phage applied to tomato roots was also evaluated. Several experiments were conducted applying either single phages or phage mixtures specific for Ralstonia solanacearum, Xanthomonas perforans or X. euvesicatoria to soil surrounding tomato plants and measuring the persistence and translocation of the phages over time. In general, all phages persisted in the roots of treated plants and were detected in stems and leaves; although phage level varied and persistence in stems and leaves was at a much lower level compared with persistence in roots. Bacterial wilt control was typically best if the phage or phage mixtures were applied to the soil surrounding tomatoes at the time of inoculation, less effective if applied 3 days before inoculation, and ineffective if applied 3 days after inoculation. The use of an attenuated X. perforans strain was also evaluated to improve the persistence of phage populations on tomato leaf surfaces. In greenhouse and field experiments, foliar applications of an attenuated mutant X. perforans 91-118:∆OPGH strain prior to phage applications significantly improved phage persistence on tomato foliage compared with untreated tomato foliage. Both the soil-based bacteriophage delivery and the use of attenuated bacterial strains improved bacteriophage persistence on respective root and foliar tissues, with evidence of translocation with soil-based bacteriophage applications. Both strategies could lead to improved control of bacterial pathogens on plants.

Visualisation of hrp gene expression in Xanthomonas euvesicatoria in the tomato phyllosphere

The plasmid pUFZ75 conferred constitutive GFP expression on the bacterial pathogen Xanthomonas euvesicatoria (syn. X. campestris pv. vesicatoria). Colonisation of the tomato phyllosphere and invasion of tomato leaves by X. euvesicatoria was examined using both fluorescence and confocal laser scanning microscopy. Xanthomonas euvesicatoria established a limited population on the tomato leaf surface, primarily occupying the depressions between epidermal cells and around the stomata, prior to invasion of the leaf via the stomata and subsequent growth within the substomatal chamber and the leaf apoplast. Additionally, hrp-gfp fusions were used to report on the temporal and spatial expression of hrp genes during epiphytic colonisation and invasion. Xanthomonas euvesicatoria cells carrying hrpG- and hrpX-gfp reporter constructs were not fluorescent in vitro on non-hrp-inducing LB agar but did exhibit a low level of fluorescence on the leaf surface within 24 h of inoculation, particularly in the vicinity of stomata. Cells carrying hrpG- and hrpX-gfp fusions exhibited high levels of fluorescence 72 h after inoculation in the substomatal chamber and the leaf apoplast. Cells carrying the hrpF-gfp fusion were slightly fluorescent on LB agar and showed no further increase in fluorescence on the leaf surface by 24 h after inoculation, but did show a significant increase in fluorescence 72 h after inoculation in the substomatal chamber and apoplast. The apparent low-level induction of the regulators hrpG and hrpX on the tomato leaf surface may suggest that some of the genes of the X. euvesicatoria HrpG/HrpX regulon are up- or down-regulated prior to invasion of the stomata while still on the leaf surface.

Higher glandular trichome density in tomato leaflets and repellence to spider mites

The objective of this work was to evaluate the feasibility of selection for higher glandular trichome densities, as an indirect criterion of selection for increasing repellence to spider mites Tetranychus urticae, in tomato populations derived from an interspecific cross between Lycopersicon esculentum x L. hirsutum var. glabratum PI 134417. Trichome densities were evaluated in 19 genotypes, including 12 from advanced backcross populations, derived from the original cross L. esculentum x L. hirsutum var. glabratum PI 134417. Counts were made both on the adaxial and abaxial leaf surfaces, and trichomes were classified into glandular types IV and VI, other glandular types (types I+VII), and nonglandular types. Mite repellence was measured by distances walked by mites onto the tomato leaf surface after 20, 40 and 60 min. Spider mite repellence biotests indicated that higher densities of glandular trichomes (especially type VI) decreased the distances walked by the mites onto the tomato leaf surface. Selection of plants with higher densities of glandular trichomes can be an efficient criterion to obtain tomato genotypes with higher resistance (repellence) to spider mites.

Factors affecting survival of bacteriophage on tomato leaf surfaces.

The ability of bacteriophage to persist in the phyllosphere for extended periods is limited by many factors, including sunlight irradiation, especially in the UV zone, temperature, desiccation, and exposure to copper bactericides. The effects of these factors on persistence of phage and formulated phage (phage mixed with skim milk) were evaluated. In field studies, copper caused significant phage reduction if applied on the day of phage application but not if applied 4 or 7 days in advance. Sunlight UV was evaluated for detrimental effects on phage survival on tomato foliage in the field. Phage was applied in the early morning, midmorning, early afternoon, and late evening, while UVA plus UVB irradiation and phage populations were monitored. The intensity of UV irradiation positively correlated with phage population decline. The protective formulation reduced the UV effect. In order to demonstrate direct effects of UV, phage suspensions were exposed to UV irradiation and assayed for effectiveness against bacterial spot of tomato. UV significantly reduced phage ability to control bacterial spot. Ambient temperature had a pronounced effect on nonformulated phage but not on formulated phages. The effects of desiccation and fluorescent light illumination on phage were investigated. Desiccation caused a significant but only slight reduction in phage populations after 60 days, whereas fluorescent light eliminated phages within 2 weeks. The protective formulation eliminated the reduction caused by both of these factors. Phage persistence was dramatically affected by UV, while the other factors had less pronounced effects. Formulated phage reduced deleterious effects of the studied environmental factors.

Effect of tomato leaf traits on the potato tuber moth and its predominant larval parasitoid: A mechanism for enemy-free space

Tomato plants are thought to provide the potato tuber moth (PTM), Phthorimaea operculella (Zeller) (Lepidoptera: Gelechiidae), with enemy-free space. The present study was aimed at assessing the role of plant surface factors in lowering enemy activity or efficiency on tomato plants. Specifically, we tested: (i) the compatibility of plant resistance traits and parasitoid activity in tomato; (ii) whether tomato leaf surface factors affect the main parasitoid species of PTM larvae to a larger extent than they would the host; and (iii) whether plant traits act on the parasitoid directly or indirectly, through the host. Results indicate that the settling response of PTM neonates on tomato leaves was not affected by trichome density and was similar on the three tested tomato cultivars. The parasitoid Diadegma pulchripes , however, failed to parasitize PTM larvae actively feeding in tomato leaves, whereas it successfully parasitized 46% of larvae feeding in potato leaves. Yet the parasitoid was not affected by the plants indirectly, through the hosts; both tomato- and potato-fed larvae were equally accepted by and suitable for the parasitoid when offered in the absence of the host plants. It can be concluded that factors associated with tomato leaves, such as glandular trichomes, have no effect on the larval establishment of PTM on the plant, but they do have a direct adverse effect on D. pulchripes , the primary PTM biological control agent in the system. In cultivated tomato, therefore, leaf traits which may confer resistance to generalist herbivores but not to the oligophagous PTM may not be compatible with natural enemies of these pests.

An SEM study of the structure and classification of the leaf trichomes in the genusLycopersicon(tomato)

Species of the genusLycopersiconcharacteristically possess pubescent leaves; seven types of trichomes were described in 1943, based on light microscopic observations. Recently, there has been renewed interest in trichomes since the presence and density of certain types of trichomes has been related to insect resistance in some species and/or varieties of tomato.Trichomes can be divided into two functional categories, depending on whether the tips are pointed or glandular. Within each of these categories, trichome types have been further differentiated according to the length and number of cells in the stalk and the complexity of the basal structure. Three non-glandular and four glandular types have been described inLycopersicon.Our SEM observations of tomato leaf surfaces suggest that there may be a need to re-evaluate Luckwill's classification of trichome types.

Chemotaxis by Pseudomonas syringae pv. tomato

Optimal laboratory conditions for studying chemotaxis by Pseudomonas syringae pv. tomato were determined by using the Adler capillary tube assay. Although they are not an absolute requirement for chemotaxis, the presence of 0.1 mM EDTA and 1 mM MgCl(2) in the chemotaxis buffer (10 mM potassium phosphate [pH 7.2]) significantly enhanced the response to attractant. The addition of mannitol as an energy source had little effect. The optimal temperature for chemotaxis was 23 degrees C, which is 5 degrees C below the optimal growth temperature for this pathogen. The best response occurred when the bacteria were exposed to attractant for 60 min at a concentration of approximately 5 x 10 CFU/ml. P. syringae pv. tomato was strongly attracted to citric and malic acids, which are the predominant organic acids in tomato fruit. With the exception of asparagine, the major amino acids of tomatoes were weak to moderate attractants. Glucose and fructose, which account for approximately 47% of tomato dry matter, also elicited poor responses. In assays with tomato intercellular fluid and leaf surface water, the bacterial speck pathogen could not chemotactically distinguish between a resistant and a susceptible cultivar of tomato.