Young Tomato Plants Research Articles

Foliar applications of fertilizer salts inhibit powdery mildew on tomato1

Foliar applications of a number of inorganic fertilizer salts were found to significantly reduce powdery mildew [Erysiphe orontii] on greenhouse tomato (Lycopersicon esculentum, cv. Trust) leaves. In a series of single-application experiments, the foliar applications, each with 0.1% surfactant, were applied to the third and fourth leaves of young tomato plants 24 h before inoculation with an atomized application of mildew conidia. Control treatments consisted of a water application and a water plus surfactant application. Powdery mildew colonies were counted 7–10 days later. Surfactant alone significantly reduced mildew colony numbers. CaCl2, Ca(NO3)2, and K2HPO4 reduced colony counts compared with the surfactant alone. All combinations of Ca salts, or Ca salts plus elemental S, significantly reduced mildew colony counts compared with surfactant alone. In a second set of experiments, the effects of repeated applications on already naturally infected tomato plants were evaluated. Young tomato plants were moved to a greenhouse containing several heavily mildew-infected tomato plants, allowing natural infection. The following day and every 7–10 days thereafter, treatments were applied to all leaves. Colony counts on selected leaves were made weekly or just before spraying. Surfactant alone was not as effective as in the single-application treatments, often having no effect. All the Ca-salt treatments that were effective in the single-application series were effective as multiple applications. Repeated applications of combinations of Ca salts were often just as effective as applications of elemental S. KCl, MgSO4, and K2HPO4 also significantly reduced mildew counts with multiple applications. This study did not attempt to explain the differences or similarities in efficacy of the salts tested; both osmotic (concentration) and specific-ion effects could play a role.

Electrophysiological characterization of tomato hypocotyl putative action potentials induced by cotyledon heating

Young tomato plants (Lycopersicon esculentum, 8 days old) were given a heat-wound to a cotyledon. The resulting electrical activity at the hypocotyl level was monitored with intracellular microelectrodes. We observed an original pattern of slow wave potentials (SWPs), consisting of 2-3 slow waves, with associated spikes. The electrophysiological study of the SWPs confirms previous conclusions that the SWPs are due to the inhibition of an active component of the membrane potential. The electrophysiological study of the spikes shows that they fit particularities of putative action potentials (APs). They seem to be triggered by the depolarization accompanying the SWPs and thus can appear late during the SWP. An ionic characterization of the spikes by using different extracellular ionic concentrations and channel blockers suggests that anionic channels might be involved, carrying SO42- ions. The channels activity might be down regulated by the calcium released by the vacuole during the SWPs and APs. A better characterization of the nature of these APs could permit the understanding of the information transmission mechanisms in higher plants.

Use of a Hydrophobic Particle Film as a Barrier to Extrinsic Ice Nucleation in Tomato Plants

Extrinsic ice nucleating agents (such as ice-nucleation-active bacteria, dew, etc.) significantly limit the ability of herbaceous plants to supercool. It is believed that with an absence of these extrinsic nucleating agents, a plant could supercool to less than -4 °C. Other evidence, however, indicates that intrinsic nucleating agents may limit the extent of supercooling. Infrared video thermography was used to study freezing in young, `Rutgers' tomato (Lycopersicon esculentum L.) plants and to determine if a hydrophobic barrier on the plant surface could prevent extrinsic nucleating agents such as Ice+ bacterial strain (Cit7) of Pseudomonas syringae Van Hall from initiating freezing within a plant. Freezing tests were conducted in a programmable freezing chamber, a radiative frost chamber, and outdoors. Freezing was visualized and recorded on videotape using an infrared radiometer. Freezing of the plants was induced extrinsically by application of droplets (5 to 7 μL) of water containing Cit7. To provide a barrier to the action of extrinsic ice nucleating agents, an emulsion of hydrophobic kaolin (aluminum silicate mineral) was applied to the plant surface before application of an extrinsic nucleating agent. Results indicate that dry, young tomato plants can supercool to as low as -6 °C whereas plants having a single droplet of Cit7 would freeze at -1.5 to -2.5 °C. Application of the hydrophobic barrier blocked the effect of Cit7 and allowed whole plants to also supercool to -6 °C, despite the presence of frozen droplets on the leaf surface. When whole plants were sprayed with water and Cit7 using an aerosol sprayer and exposed to -3 °C, plants coated with the hydrophobic particle film exhibited significantly less foliar injury then nontreated plants. Similar results were obtained using the radiative frost chamber. Experiments conducted under natural frost conditions also resulted in less injury to the coated plants. The hydrophobic kaolin particle film performed better at preventing plants from freezing due to extrinsic ice nucleation than nonaltered, hydrophyllic kaolin alone or an antitranspirant with putative frost protection properties.

Interactive effects of nitrogen and irradiance on growth and partitioning of dry mass and nitrogen in young tomato plants.

The interactive effects of irradiance and N on growth of young tomato plants (Lycopersicon esculentum Mill.) were studied. Plants were grown at 70 or 300 μmol photons m-2 s-1, hereafter referred to as 'low' and 'high' irradiance, and at a range of exponential N supply rates (70-370 mg g-1 d-1) or at a constant concentration in the nutrient solution of 12 mM NO3-. At both irradiance levels, leaf area ratio was more important than net assimilation rate (NAR) in explaining effects of N on growth at mild N limitation. However, at severe N limitation, NAR became the most important parameter, as indicated by calculated growth response coefficients. Furthermore, this study shows that N supply and growth irradiance interacted strongly. The decrease of specific leaf area with increasing N limitation and increasing growth irradiance correlated with increasing leaf dry mass percentage and starch concentration. Furthermore, at low irradiance, plants partitioned more dry mass to the stem. Dry mass partitioning to roots increased with decreasing plant N concentration, and this relation appeared to be independent of irradiance. Shading increased plant N concentration and decreased dry mass partitioning to roots. Also, the relationship between plant N concentration and N partitioning to different plant organs was largely independent of growth irradiance.

Growth and dry‐mass partitioning in tomato as affected by phosphorus nutrition and light

AbstractWe studied the effects of phosphorus (P) and light on the physiological and morphological components of growth of young tomato plants (Lycopersicon esculentum Mill. cv. Capita). The importance of dry‐mass partitioning and starch accumulation in explaining the effects of P limitation on growth was examined more closely. Plants were grown at a wide range of exponential P supply rates (between 70 and 320 mg g−1 d−1) and one free‐access treatment (1 mm). Two light levels (70 and 300 µmol m−2 s−1) were applied. Growth response coefficients (GRCs) were calculated to address the importance of different growth parameters in explaining relative growth rate (RGR). At both light levels, net assimilation rate (NAR) was more important than leaf area ratio (LAR) in explaining the effects of P on growth as indicated by GRCs. At less severe P limitation, LAR became more important and NAR less important. Dry‐mass partitioning to both roots and leaves played a minor role in determining the effects of P limitation on growth as indicated by low GRCs. The increase in starch at mild P limitation showed that the assimilate supply was not limiting. At severe P limitation, the rate of photosynthesis was decreased, as suggested by the decrease in starch accumulation.

Expression of the Fusarium resistance gene I-2 colocalizes with the site of fungal containment.

The tomato resistance gene I-2 is one of at least six members of a gene family that are expressed at low levels in the roots, stems and leaves of young tomato plants. Plants transformed with constructs containing a functional I-2 promoter fused to the beta-glucuronidase (GUS) reporter gene were used in detailed expression studies. Highest GUS activity was found in stems of young tomato plants. Histochemical analysis revealed that the I-2 promoter drives expression of the reporter gene in vascular tissue of fruits, leaves, stems and mature roots. In younger roots, expression was most abundant at the base of lateral root primordia. Microscopical analysis of young tomato plants revealed expression in tissue surrounding the xylem vessels. We show that in resistant plants, fungal growth into this region of the vascular tissue is prevented, suggesting a correlation with the I-2-mediated resistance response.

189 The Use of Hydrophobic Clay Films as a Barrier to Ice Nucleation in Plants

Most plants exhibit the ability to supercool to some extent without freezing. The extent of supercooling, however, is limited by the action of intrinsic and extrinsic ice nucleating agents which initiate ice formation and propagation within a plant at relatively warm subzero temperatures (-1.5 to -3.5 °C). In herbaceous plants, extrinsic ice-nucleating agents (such as ice-nucleation bacteria, dew, and other good nucleating agents) significantly limit the ability to supercool below 0 °C. It is believed that with an absence of these extrinsic nucleating agents that plants could supercool to less than -4 °C. Other evidence indicates that intrinsic nucleating agents may also significantly limit the extent of supercooling. Questions also exist about nucleation in woody plants and especially the new growth (flowers, leaves, and shoots) present in spring. A better understanding of how freezing is initiated in plants has been limited by the inability to determine and visualize the initial site of ice nucleation and pattern of ice propagation. We have used infrared video thermography to study freezing in young tomato (Lycopersicon esculentum) plants and to determine if a hydrophobic barrier on the plant surface could prevent the action of extrinsic nucleating agents such as Ice + bacterial strain (Cit7) of Pseudomonas syringae from initiating freezing within a plant. Tomato plants were grown in a greenhouse in individual pots and used when they were 4 to 6 weeks old. Freezing tests were conducted in a programmable freezing chamber, and freezing was visualized and recorded on videotape using an infrared radiometer. Freezing of the plants was extrinsically induced by the application of droplets (5 μl) of water containing Cit7. To provide a barrier to the action of extrinsic ice-nucleating agents, an emulsion of hydrophobic kaolin was applied to the plant surface before applying an extrinsic nucleating agent. Results indicate that dry, young tomato plants can supercool to as low as -6 °C whereas plants having a single droplet of Cit7 would freeze at -1.5 to -2.5 °C. Applying the hydrophobic barrier blocked the effect of Cit7 and allowed the plants to also supercool to -6 °C, despite the presence of frozen droplets. Experiments under natural freezing conditions are in progress.

Effects of isolate virulence and host susceptibility on development of early blight (Alternaria solani) on tomato*

Early blight of tomato (Lycopersicon esculentum) caused by Alternaria solani has the potential to become one of the most serious diseases throughout the tomato‐producing regions of Greece. Controlled environment experiments were conducted to study the virulence of A. solani isolates and the susceptibility of commercial tomato cultivars and hybrids to early blight. The isolates used, derived from naturally infected tomato plants during the period 1997/1998, differed significantly (P>0.05) in the rate of mycelial growth as well as in their ability to sporulate in vitro. No correlation (R2= 0.33) was found between mycelial growth and conidia production. Isolates of A. solani were virulent to young tomato plants (cv. Ace 55VF), although they differed significantly (P>0.05) in the intensity of symptoms produced on leaves, stems, petioles and flowers. Defoliation was linearly related (R2= 0.87) to the percentage of leaf area with symptoms. Twenty‐three tomato cvs. or F1 hybrids were evaluated for their susceptibility to early blight. The cultivars or hybrids were arbitrarily categorized as immune, highly tolerant, tolerant, moderately tolerant, susceptible and highly susceptible based on a percent disease index range: 0%, 1‐9%, 10‐24%, 25‐49%, 50‐74% and 75% or more respectively. None of the cultivars or hybrids tested was immune or tolerant to A. solani infection.

UVB/UVA radiation activates a 48 kDa myelin basic protein kinase and potentiates wound signaling in tomato leaves.

We investigated the effect of UV radiation on early signaling events in the response of young tomato plants (Lycopersicon esculentum) to wounding. Ultraviolet-C (< 280 nm) and UVB/UVA (280-390 nm) radiation both induced 48 kDa myelin basic protein kinase activity in leaves. The activation was associated with phosphorylation of tyrosine residues on the kinase, which is indicative of protein kinases of the mitogen-activated protein kinase family. Ultraviolet-C irradiation resulted in a strong proteinase inhibitor synthesis, as reported previously (Conconi et al., Nature 383, 826-829, 1996). Under the conditions used, UVB/UVA radiation did not induce proteinase inhibitor synthesis but resulted in a strong potentiation of systemic proteinase inhibitor synthesis in response to wounding. The UVB/UVA-irradiated plants that were subsequently wounded accumulated 2.5-4-fold higher levels of proteinase inhibitor I when compared to wounded non-irradiated plants. The potentiating effect was most prominent in the systemic unwounded leaf of a wounded plant. Levels of 12-oxo-phytodienoic acid and jasmonic acid that have been well documented to increase in response to wounding were not detected in response to UVB/UVA irradiation alone. The effect of UVB/UVA radiation in potentiating plant defense signaling should be further considered as a factor that may influence the ecological balance between plants and their predators.

Proteinase inhibitor-inducing activity of the prohormone prosystemin resides exclusively in the C-terminal systemin domain.

Prosystemin is the 200-amino acid precursor of the 18-amino acid polypeptide defense hormone, systemin. Herein, we report that prosystemin was found to be as biologically active as systemin when assayed for proteinase inhibitor induction in young tomato plants and nearly as active in the alkalinization response in Lycopersicon esculentum suspension-cultured cells. Similar to many animal prohormones that harbor multiple signals, the systemin precursor contains five imperfect repetitive domains N-terminal to a single systemin domain. Whether the five repetitive domains contain defense signals has not been established. N-terminal deletions of prosystemin had little effect on its activity in tomato plants or suspension-cultured cells. Deletion of the C-terminal region of prosystemin containing the 18-amino acid systemin domain completely abolished its proteinase inhibitor induction and alkalinization activities. The apoplastic fluid from tomato leaves and the medium of cultured cells were analyzed for proteolytic activity that could process prosystemin to systemin. These experiments showed that proteolytic enzymes present in the apoplasm and medium could cleave prosystemin into large fragments, but the enzymes did not produce detectable levels of systemin. Additionally, inhibitors of these proteolytic enzymes did not affect the biological activity of prosystemin. The cumulative data indicated that prosystemin and/or large fragments of prosystemin can be active inducers of defense responses in both tomato leaves and suspension-cultured cells and that the only region of prosystemin that is responsible for activating the defense response resides in the systemin domain.

A 160-kD systemin receptor on the surface of lycopersicon peruvianum suspension-cultured cells

Systemin, an 18-amino acid polypeptide wound signal, activates defense genes in leaves of young tomato plants and induces rapid alkalinization of media containing suspension-cultured Lycopersicon peruvianum cells. A monoiodinated form of a systemin analog synthesized with Tyr-2 and Ala-15 (Tyr-2,Ala-15-systemin) likewise exhibits similar biological activities. (125)I-Tyr-2,Ala-15-systemin rapidly, reversibly, and saturably bound to suspension-cultured L. peruvianum cells with a K(d) of 0.17 nM and a Hill coefficient of 0. 92. The specificity of binding was assessed with alanine-substituted systemin analogs and was found to correlate with their respective biological activities. Treatment of suspension-cultured cells with methyl jasmonate increased the total binding of (125)I-Tyr-2, Ala-15-systemin more than threefold, suggesting that methyl jasmonate was activating transcription of the gene encoding the binding protein. Treatment of cells with cycloheximide markedly decreased binding of iodinated systemin to the cells, indicating that the binding protein was constantly being synthesized and degraded. A photoaffinity systemin analog, N-(4-[p-azidosalicylamido]butyl)-3'(2'-Cys-3, Ala-15-systemindithiol)propionamide, specifically labeled a 160-kD cell surface protein, and the labeling was completely inhibited by a 20-fold excess of unlabeled systemin. These data indicate that a 160-kD protein may be the physiological receptor for systemin in suspension-cultured cells.

Carbon balance of a whole tomato plant and the contribution of source leaves to sink growth using the CO2 steady‐state feeding method

To clarify the entire carbon balance of a young tomato plant and the contribution of each leaf to sink growth, the carbon balance of each leaf was quantitatively measured using the CO2 steady‐state feeding method to quantitatively measure the photosynthesis, translocation, distribution and respiration of newly fixed C. The entire carbon balance of the whole plant was calculated by adding the data of each leaf. The total amount of carbon fixed by all source leaves was 70.2 mg. Of this amount, in a 24‐h period, 29% was accumulated in the sinks, 28% remained in the source leaves and 42% was respired. Of the total amount of carbon accumulated in the sinks, the proportion accumulated in the shoot apex, stem and roots were 27, 40 and 29%, respectively. The third and fourth leaves contributed about 30–40% of the total growth of the main sinks. The distribution pattern of each leaf to the shoot apex of the plant was greatest in the first leaf and decreased with decreasing leaf age, whereas it showed an opposite trend in the roots.

Wound- and systemin-inducible calmodulin gene expression in tomato leaves.

Using a calmodulin (CaM) cDNA as a probe in northern analyses, transgenic tomato plants that overexpress the prosystemin gene were found to express increased levels of CaM mRNA and protein in leaves compared to wild-type plants. These transgenic plants have been reported previously to express several wound-inducible defense-related genes in the absence of wounding. Calmodulin mRNA and protein levels were found to increase in leaves of young wild-type tomato plants after wounding, or treatment with systemin, methyl jasmonate, or linolenic acid. CaM mRNA appeared within 0.5 h after wounding or supplying young tomato plants with systemin, and peaked at 1 h. The timing of CaM gene expression is similar to the expression of the wound- or systemin-induced lipoxygenase and prosystemin genes, signal pathway genes whose expression have been reported to begin at 0.5-1 h after wounding and 1-2 h earlier than the genes coding for defensive proteinase inhibitor genes. The similarities in timing between the synthesis of CaM mRNA and the mRNAs for signal pathway components suggests that CaM gene expression may be associated with the signaling cascade that activates defensive genes in response to wounding.

Preparation and use of monoclonal antibodies to detect Phytophthora nicotianae var. nicotianae

A monoclonal antibody (MAb 18) was prepared against purified mycelial proteins from Phytophthora nicotianae var. nicotianae. The specificity of MAb 18 (lgG class) was tested using indirect ELISA (PTA-ELISA).It cross-reacted with Phytophthora cacto­ rum, P. cinrzamomi, P. cryptogea, P. fragariae) but not with other fungi (Fusarium oxysporum, Pythium ultimwn and P. oligan­ drwn) and bacteria (Clavibacter michiganensis subsp. michiganensis) isolated from tomato. Phytophthora nicotianae var. nicotianae was detected in roots and basal stems of artificially infected young tomato plants using indirect ELISA and immunoprinting.

Critical nutrient concentrations and antagonistic and synergistic relationships among the nutrients of NFT‐grown young tomato plants

Critical concentrations of nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), iron (Fe), zinc (Zn), and manganese (Mn) with respect to dry matter yield end antagonistic and synergistic relationships among these nutrients were studied in which tomato (Lycopersicon esculentum L.) was grown in recirculating nutrient solution (NFT). Increments of nutrient elements in the nutrient solution increased the proportional rate of the corresponding nutrient elements. Increasing levels of N negatively correlated with plant P and positively correlated with Ca, Fe, and Zn. Iron and Mn contents of the plants were increased and N, K, Ca, and Mg were decreased as a function of P applied. Increases in K in the nutrient solution caused increases in the concentrations of K, N, P, and Zn, and decreases in the concentration of Ca and Fe. Applied Ca increased the concentrations of Ca and N, and decreased the concentrations of P, Mg, Fe, Zn, and Mn. Potassium, Ca, and Fe contents of the plants were decreased and Zn increased, while N, P, and Mn were not affected by the increasing levels of external Mg. Iron suppressed the plant Mg, Zn, and Mn contents. Synergism between Zn and Fe was seen, while P, K, Ca, Mg, and Mn contents were not affected by Zn levels. Potassium, Ca, Mg, and Fe were not responsive to applied Mn, however, N and P contents of the plants were decreased at the highest levels of Mn.

Comparison of sole carbon source profiles monitored at two different wavelengths

Profiles of sole carbon source utilization are increasingly used to characterize microbial communities in various environments. Metabolization of a single carbon source is detected by monitoring a colorimetric reaction. In most work, either of two different wavelengths, 405 or 590 nm, has been employed for detection. In the present study we compared the outcome of these two detection modes applied to a study of the influence of plant growth-promoting rhizobacteria on the root-inhabiting microbial communities on the roots of young tomato plants. The results showed different average well color development and number of positive wells when detected at the two wavelengths with respect to the development of the single curve, absolute values and standard deviation. Further, the carbon source that was utilized the most by the rhizosphere microflora was not congruent between the two reading modes. The overall results, however, were similar, as evaluated by multivariate statistics. In conclusion, this study indicates that the carbon source utilization profiles should be standardized with respect to the wavelength used to enable comparability or development of models on the microbial status in ecosystems.

Effect of Nitrogen Availability on Expression of Constitutive and Inducible Chemical Defenses in Tomato, Lycopersicon esculentum

Young tomato plants (Lycopersicon esculentum) grown in sand in a greenhouse and subjected to different fertilization regimes were used to test the effects of nitrogen availability on constitutive levels of phenolics and on constitutive and inducible activities of polyphenol oxidase and proteinase inhibitors. Theories that emphasize physiological constraints on the expression of phytochemicals predict an increase in levels of carbon-based allelochemicals under moderate nitrogen stress but predict, under the same conditions, an attenuation of chemical responses involving nitrogen-containing compounds such as proteinase inhibitors and polyphenol oxidase. We found that nitrogen availability had a strong effect on constitutive levels of phenolics; weaker effects on constitutive polyphenol oxidase activity, constitutive proteinase inhibitor activity, and inducible polyphenol oxidase activity; and no effect on inducible proteinase inhibitor activity. These results point to a need for the integration of theories that emphasize physiological influences on secondary metabolism with those that emphasize ecological influences on secondary metabolism and suggest that current theories of plant defense do not adequately account for enzymatic and proteinaceous defenses against arthropods.

Myelin basic protein kinase activity in tomato leaves is induced systemically by wounding and increases in response to systemin and oligosaccharide elicitors.

In response to wounding, a 48-kDa myelin basic protein (MBP) kinase is activated within 2 min, both locally and systemically, in leaves of young tomato plants. The activating signal is able to pass through a steam girdle on the stem, indicating that it moves through the xylem and does not require intact phloem tissue. A 48-kDa MBP kinase is also activated by the 18-amino acid polypeptide systemin, a potent wound signal for the synthesis of systemic wound response proteins (swrps). The kinase activation by systemin is strongly inhibited by a systemin analog having a Thr-17 --> Ala-17 substitution, which is a powerful antagonist of systemin activation of swrp genes. A 48-kDa MBP kinase activity also increases in response to polygalacturonic acid and chitosan but not in response to jasmonic acid or phytodienoic acid. In def1, a mutant tomato line having a defective octadecanoid pathway, the 48-kDa MBP kinase is activated by wounding and systemin as in the wild-type plants. This indicates that MBP kinase functions between the perception of primary signals and the DEF1 gene product. In response to wounding, the MBP kinase is phosphorylated on phosphotyrosine residues, indicating a relationship to the mitogen-activated protein kinase family of protein kinases.

A New Geminivirus Associated with Tomato in the State of São Paulo, Brazil.

The apical growth of about 20% of young tomato plants in observed fields near Campinas, State of São Paulo, Brazil, had yellow streaking of veins. Leaf symptoms developed into patches of yellow mosaic and the leaves became wavy. The whitefly Bemisia tabaci Genn. transmitted a pathogen from the infected tomato plants to healthy tomato and potato plants, reproducing the original symptoms in tomato. The apical leaves of infected potatoes showed yellow or green mottle that developed into leaf distortion with yellow blotches, symptoms indistinguishable from potato-deforming mosaic disease (2). DNA was extracted from these tomato and potato plants (1). Using DNA from the infected tomato plant, polymerase chain reaction (PCR) with the degenerate primer pair PAC1v1978/ PAV1c715 (1), which amplifies part of the rep gene (AC1 ORF), the common region (CR), and part of the cp gene (AV1 ORF), and with the primer pair PBC1v2039/PBV1c800, which amplifies part of BC1 ORF, CR, and part of BV1 ORF, gave virus-specific DNA fragments of the sizes expected from a whitefly-transmitted geminivirus. These were cloned and the complete nucleotide (sequences for DNA-A (pToYA, GenBank accession no. U79998) and DNA-B (pToYB, GenBank accession no. U80042) fragments obtained. Nucleotide identity between the CRs (184 nucleotides) was 90%, strongly indicating that those fragments correspond to a bipartite subgroup III geminivirus. PCR with the DNA from infected potato gave the expected size fragment for DNA-A. The partial sequence of the rep gene was 100% identical to the homologous sequence from the PCR fragment from the infected tomato. A search in the GenBank, EMBL, DDBJ, and PDB databases, using the BLAST program, found no identical geminivirus. The highest identity for the CR was 75% to tomato mottle geminivirus-Florida (ToMoV) and 74% to bean golden mosaic virus-Brazil. For the rep gene, the highest identity was 73% to tomato yellow leaf curl virus-Israel, an Old World geminivi-rus, followed by 71% to tomato golden mosaic virus-Brazil (TGMV) and ToMoV. For the cp gene, the highest identity was 86% to TGMV, followed by 83% to squash leaf curl geminivirus. Therefore, we propose the name tomato yellow vein streak geminivirus (ToYVSV) for this distinct virus (2).

First Report of Powdery Mildew in Greenhouse-Grown Tomatoes in New Jersey.

Powdery mildew of tomatoes caused by an Erysiphe sp. has been reported to occur in greenhouses in New York (2). In March and April of 1996, outbreaks of this disease were found in greenhouse-grown tomato plants of cv. PSR55809 at the Cook College campus in New Brunswick, NJ, and in cv. Match in commercial greenhouses in Burlington County, NJ. Identification of an Erysiphe sp. was made by comparative morphology of the conidial state since the perfect stage was not observed. Symptoms included development of patches of white mycelium predominantly on upper surfaces of older leaves followed by chlorosis of tissues colonized by the fungus. Microscopic examination of mycelium revealed the presence of typical Oidium conidiogenous cells and conidia. Conidiogenous cells were short and cylindrical and produce conidia in chains apically. Conidia were hyaline, cylindrical to ellipsoidal, and measured 36 + 4.9 × 16.7 + 2.2 μm (n = 20). Both conidia and symptoms of this powdery mildew are comparable to those previously given for the Erysiphe sp. described in New York (2). Another powdery mildew of tomato, caused by Oidiopsis sicula Scalia, occurs in the western U.S., Mediterranean Basin, Africa, and Asia. However, the conidia of O. sicula are of two types, pyriform and cylindrical, and they are larger than those of an Erysiphe sp. (1). To verify pathogenicity of this Erysiphe sp. to tomatoes, conidia washed from leaves were misted onto uninfected leaves of young tomato plants. After 1 week in a growth chamber (25°C; 80% relative humidity; 12 h of light), typical powdery mildew symptoms were evident on inoculated plants, while unmisted plants remained free of symptoms. Microscopic examination of the fungus on surfaces of leaves confirmed it to be an Erysiphe sp.