California Tomato Research Articles

Molecular and Biological Characterization of Tomato mottle mosaic virus and Development of RT-PCR Detection

Tomato mottle mosaic virus (ToMMV) was first identified in 2013 as a novel tobamovirus infecting tomatoes in Mexico. In just a few years, ToMMV has been identified in several countries around the world, including the United States. In the present study, we characterized the molecular, serological, and biological properties of ToMMV and developed a species-specific RT-PCR to detect three tomato-infecting tobamoviruses: Tobacco mosaic virus (TMV), Tomato mosaic virus (ToMV), and ToMMV. Previously, ToMMV has been reported in Florida and New York. In this study, we made two new reports on the occurrences of ToMMV on tomatoes in California and South Carolina. Their complete genome sequences were obtained and their genetic relationships to other tobamoviruses evaluated. In host range studies, some differential responses in host plants were also identified between ToMMV and ToMV. To alleviate cross-serological reactivity among the tomato-infecting tobamoviruses, a new multiplex RT-PCR was developed to allow for species-specific detection and identification of TMV, ToMV, and ToMMV. In addition, we observed resistance breaking by ToMMV on selected tomato cultivars that were resistant to ToMV. This has caused serious concerns to tomato growers worldwide. In conclusion, the characterization in molecular and biological properties of ToMMV would provide us with fundamental knowledge to manage this emerging virus on tomato and other solanaceous crops in the U.S. and around the world.

First Report of Bacterial Leaf Spot Caused by Pseudomonas syringae pv. tomato on Kale in California

HomePlant DiseaseVol. 101, No. 3First Report of Bacterial Leaf Spot Caused by Pseudomonas syringae pv. tomato on Kale in California PreviousNext DISEASE NOTES OPENOpen Access licenseFirst Report of Bacterial Leaf Spot Caused by Pseudomonas syringae pv. tomato on Kale in CaliforniaS. T. Koike, E. I. Alger, L. Ramos Sepulveda, and C. T. BullS. T. KoikeSearch for more papers by this author, E. I. AlgerSearch for more papers by this author, L. Ramos SepulvedaSearch for more papers by this author, and C. T. BullSearch for more papers by this authorAffiliationsAuthors and Affiliations S. T. Koike , University of California Cooperative Extension, Salinas 93901 E. I. Alger , Undergraduate Research Opportunities Center, California State University Monterey Bay, Seaside 93955 L. Ramos Sepulveda , The Pennsylvania State University, University Park 16802 C. T. Bull , The Pennsylvania State University, University Park 16802, and USDA/ARS, Salinas, CA 93901. Published Online:20 Dec 2016https://doi.org/10.1094/PDIS-10-16-1460-PDNAboutSectionsSupplemental ToolsAdd to favoritesDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InRedditEmailWechat In 2014, bacterial leaf spot was seen on commercial kale (Brassica oleracea var. acephala) grown in Monterey County, CA. Initial symptoms were small (2 to 4 mm in diameter), angular, water soaked lesions observable on both adaxial and abaxial surfaces. Lesions enlarged, became tan to light brown, and were often surrounded by chlorotic haloes. Incidence was as high as 10% and due to the impracticality of sorting healthy and diseased leaves, large portions of fields were unharvested. From macerated spots, blue-green fluorescent pseudomonads were consistently isolated on King’s Medium B agar. Six retained isolates were gram-negative, oxidase negative, arginine dihydrolase negative, produced levan, but did not nucleate ice. Isolates did not rot potato slices but induced a hypersensitive reaction on tobacco (Nicotiana tabacum cv. Samsun). These isolates therefore belong to Lelliott’s LOPAT group 1a Pseudomonas syringae (Lelliott 1966). Multilocus sequence analysis using the concatenated gene fragments of the loci gap1, gltA, gyrB, and rpoD placed the strains in P. syringae genomospecies 3, and sequences were identical to those of the pathotype of P. syringae pv. tomato. For Koch’s postulates, potted kale (cvs. Lacinato, Red Russian, Siberian) at the six-leaf stage were inoculated with bacteria grown on sucrose peptone agar for 48 h and suspended in sterile distilled water (SDW) to a concentration of 107 CFU/ml. Each of six isolates was sprayed until runoff onto 12 replicate plants per cultivar. Plants were enclosed in plastic bags for 24 h and then maintained in a greenhouse (23 to 25°C). After 4 to 5 days, water soaked lesions developed on all inoculated plants; lesions turned tan and were similar to symptoms seen in the field. Control plants sprayed with SDW developed no symptoms. Fluorescent pseudomonads were reisolated from all inoculated cultivars. The experiment was conducted twice and results were the same. The reisolates were identical to the original strains according to repetitive extragenic palindromic sequence PCR with the BOXA1R primer, confirming Koch’s postulates. Using methods described above, kale strain BS3736, P. syringae pv. tomato (CFBP2122PT), and P. syringae pv. maculicola (CFBP1657PT) were inoculated onto the three kales and tomato (cv. Super Beefsteak). In three experiments, all kale and tomato inoculated with the kale strain and the pathotype of P. syringae pv. tomato developed necrotic spots and yellow halos; distinctive pepper spot symptoms were only observed on kale cv. Lacinato inoculated with P. syringae pv. maculicola; pepper spot symptoms consist of small (3 to 4 mm in diameter), tan to brown spots visible from both sides of leaves. In this study, P. syringae pv. maculicola and P. syringae pv. tomato (including the kale strains) had overlapping but distinct experimental host ranges. P. syringae strains from kale were identified previously as P. syringae pv. maculicola though genetically identical to the pathotype strain of P. syringae pv. tomato (Zhao et al. 2000). While P. syringae has been reported on kale previously (Bull et al. 2003), this is the first report of bacterial leaf spot on kale caused by P. syringae pv. tomato in California and one of the few reports of P. syringae pv. tomato causing a natural disease outbreak on crucifers.

A life cycle assessment of biosolarization as a valorization pathway for tomato pomace utilization in California

The California tomato processing industry produced circa 388,856 t of tomato pomace in 2014. While currently used for animal feed, tomato pomace could be utilized for biosolarization. Primary Energy Demand (PED) and Global Warming Potential (GWP) equivalent emissions were calculated for two valorization pathways: (i) feed for cattle; and (ii) biosolarization. In order to make these two valorization pathways comparable three management options were analyzed whereby each part of the system was satisfied, i.e. a pest management sub-system and a cattle feed sub-system. The management options were (1) tomato pomace used for cattle feed and soil pest control using fumigant Telone II and herbicide glyphosate; (2) tomato pomace used for cattle feed and soil pest control using solarization; (3) alternative cattle feed (cottonseed, canola pellets and wheat straw) and soil pest control using biosolarization with tomato pomace. Options 2 and 3 result in a reduction of GWP and PED. Among management options, the GWP ranged from 64–98 kg CO2-e and 1502–2250 MJ for PED per t of pomace. The majority of impacts were beyond the tomato processors’ immediate control, therefore encouraging the diversion of tomato pomace to biosolarization may be desirable. Total savings per annum for biosolarization could be as large as 7.7 M kg CO2-e and 203,000 GJ annually.

First Report of Powdery Mildew Caused by Oidium lycopersici in Field-grown Tomatoes in California

First Report of Powdery Mildew Caused by <i>Oidium lycopersici</i> in Field-grown Tomatoes in California

Does mechanistic modeling of filter strip pesticide mass balance and degradation processes affect environmental exposure assessments?

Vegetative filter strips (VFS) are a widely adopted practice for limiting pesticide transport from adjacent fields to receiving waterbodies. The efficacy of VFS depends on site-specific input factors. To elucidate the complex and non-linear relationships among these factors requires a process-based modeling framework. Previous research proposed linking existing higher-tier environmental exposure models with a well-tested VFS model (VFSMOD). However, the framework assumed pesticide mass stored in the VFS was not available for transport in subsequent storm events. A new pesticide mass balance component was developed to estimate surface pesticide residue trapped in the VFS and its degradation between consecutive runoff events. The influence and necessity of the updated framework on acute and chronic estimated environmental concentrations (EECs) and percent reductions in EECs were investigated across three, 30-year U.S. EPA scenarios: Illinois corn, California tomato, and Oregon wheat. The updated framework with degradation predicted higher EECs than the existing framework without degradation for scenarios with greater sediment transport, longer VFS lengths, and highly sorbing and persistent pesticides. Global sensitivity analysis (GSA) assessed the relative importance of mass balance and degradation processes in the context of other input factors like VFS length (VL), organic-carbon sorption coefficient (Koc), and soil and water half-lives. Considering VFS pesticide residue and degradation was not important if single, large runoff events controlled transport, as is typical for higher percentiles considered in exposure assessments. Degradation processes become more important when considering percent reductions in acute or chronic EECs, especially under scenarios with lower pesticide losses.

Evaluation of the Effect of Rural Road Condition on Agricultural Produce Transportation

Road condition affects the operations and costs of vehicles that use the infrastructure. Various models of vehicle operating cost provide an indication of the effects of road roughness on fuel consumption, additional damage to a vehicle, and tire wear. These models do not include the effect of road conditions on the condition of and potential damage to transported freight. Such potential damages are mitigated through the use of improved vehicle technologies or packaging. In agricultural transportation, packaging often is not a solution because the use of older vehicle technology on mostly rural roads with lower levels of riding quality is a main contributor to the problem. This paper evaluates quantified effects of the riding quality on low-volume roads on the level of damage to tomatoes in California. The paper is partly based on a study that focused on vehicle–pavement interaction and its effects on the broader California economy. Vehicle responses to road conditions were measured during operations on a range of rural routes. Laboratory experiments were developed to replicate the dominant vibrations of the trucks and to measure the stresses that tomatoes typically undergo at these vibration levels. The damage and failure levels for the tomatoes during transportation were determined, and these damage levels were used to calculate typical costs to agricultural suppliers that are due to road conditions. The problem thus could be quantified and input data provided for a cost–benefit evaluation of the potential maintenance and improvement of various routes used to transport tomatoes.

Waste heat and water recovery opportunities in California tomato paste processing

Water and energy efficiency are important for the vitality of the food processing industry as demand for these limited resources continues to increase. Tomato processing, which is dominated by paste production, is a major industry in California – where the majority of tomatoes are processed in the United States. Paste processing generates large amounts of condensate as moisture is removed from the fruit. Recovery of the waste heat in this condensate and reuse of the water may provide avenues to decrease net energy and water use at processing facilities. However, new processing methods are needed to create demand for the condensate waste heat. In this study, the potential to recover condensate waste heat and apply it to the tomato enzyme thermal inactivation processing step (the hot break) is assessed as a novel application. A modeling framework is established to predict heat transfer to tomatoes during the hot break. Heat recovery and reuse of the condensate water are related to energy and monetary savings gained through decreased use of steam, groundwater pumping, cooling towers, and wastewater processing. This analysis is informed by water and energy usage data from relevant unit operations at a commercial paste production facility. The case study indicates potential facility seasonal energy and monetary savings of 7.3 GWh and $166,000, respectively, with most savings gained through reduced natural gas use. The sensitivity of heat recovery to various process variables associated with heat exchanger design and processing conditions is presented to identify factors that affect waste heat recovery.

Good to Think with

This article focuses on the relationships between individuals along the innovation chain that made the rapid mechanization of the tomato harvest possible in 1960s California. Based on oral histories, extension documents, trade journal stories and advertising materials, it argues that two factors enabled the rapid shift from hand to machine labor. First, the Bracero Program's political fragility combined with the economic importance of California's tomato crops to produce an imagined future shortage of labor, motivating the University of California and regional growers to prioritize research on tomato mechanization. Second, mechanizing tomatoes enabled men from different backgrounds to think in ways that were highly desirable given the era's emphasis on managerial and scientific systems. These factors worked in tandem to produce a machine that could harvest tomatoes, and a desire on the part of those who made significant investments to purchase and implement those machines, before the end of Bracero labor in 1964 crystallized the economic and socio-political rewards that would follow. By emphasizing the second set of factors, the article illuminates the importance of personal rewards in the mechanization process along the innovation chain from design, development and dissemination to implementation.

Comparing environmental impacts of regional and national-scale food supply chains: A case study of processed tomatoes

This study uses life cycle assessment methodology to quantify the energy use, greenhouse gas (GHG) emissions, and water use of processed tomato products grown, processed, and consumed within the Great Lakes region of the United States, and tomato products produced in California and then shipped to the Great Lakes region for consumption. The purpose is to assess the potential for regional food systems to reduce selected environmental impacts, particularly the energy and GHG footprints, of consumer-ready, processed food products, when compared to national-scale food systems in which consumer products are shipped long distances. The study also examines the role of different types of food processing in influencing life cycle energy use, water use, and emissions.Our results indicate that California-produced conventional and organic tomato paste and canned diced tomatoes are almost equivalent in energy use and GHG emissions to regionally produced and consumed products, but use of developed water resources is significantly higher for California-grown products. California tomato production benefits from higher per hectare yields and soil amendments with lower carbon dioxide emissions. These efficiencies substantially offset the added energy use and GHG emissions associated with long-distance shipment of products to the Great Lakes region, as long as shipments are made by rail rather than by truck. Paste, the more processed and concentrated product evaluated, amplifies any environmental advantages or disadvantages accrued in the field production stage, due to its raw tomato to finished product ratio of 6:1, suggesting that comparative regional advantage can play a role in lowering life cycle environmental impacts of highly condensed foods shipped long distances.

Assessing drivers of N2O production in California tomato cropping systems

Environmental conditions and agricultural management events affect the availability of substrates and microbial habitat required for the production and consumption of nitrous oxide (N2O), influencing the temporal and spatial variability of N2O fluxes from soil. In this study, we monitored for diurnal and event-related patterns in N2O emissions in the field, evaluated how substrate availability influenced denitrification, and assessed N2O reduction potential following major events in two tomato (Lycopersicon esculentum) management systems on clay loam soils: 1) conventional (sidedress fertilizer injection, furrow irrigation, and standard tillage) and 2) integrated (fertigation, subsurface drip irrigation, and reduced tillage). Potential denitrification activity, substrate limitation, and reduction to N2 were measured with an anaerobic slurry technique. In the field, we found no consistent diurnal patterns. This suggests that controlling factors that vary on an event-basis overrode effects of diurnally variable controls on N2O emissions. The lack of consistent diurnal patterns also indicates that measuring N2O emissions once per day following major events is sufficient to adequately assess annual N2O emissions in those systems. Nitrous oxide emissions varied per event and across functional locations in both systems. This illustrates that mechanisms underlying N2O emissions vary at relatively small temporal and spatial scales and demonstrates the importance of studying N2O emissions in the context of events and functional locations. In the conventional system, N2O fluxes were high [74.2±43.9–390.5±90.1μgN2O-Nm−2h−1] and N2O reduction potential was significant. Both management systems exhibited carbon limitation on denitrification rates; and rates were N limited in the third fertigation event in the integrated system. Our findings suggest that denitrification is strongly contributing to high N2O emissions in conventional tomato cropping systems in California. Hence, management practices that reduce the conditions that favor denitrification, such as subsurface drip irrigation, are promising strategies for N2O reduction.

Keiferia lycopersicella

<scp>K</scp>eiferia lycopersicella

Reduced nitrous oxide emissions and increased yields in California tomato cropping systems under drip irrigation and fertigation

Understanding the effect of various agricultural management practices on nitrous oxide (N2O) emissions is crucial to advise farmers and formulate policies for future greenhouse gas (GHG) reductions. In order to estimate present N2O emissions, annual N2O budgets must be thoroughly and precisely quantified from current farms under conventional and alternative management, but subject to practical and economic constraints. In this study, field sites were located on two on-farm processing tomato (Lycopersicon esculentum) fields, under contrasting irrigation managements and their associated fertilizer application strategy: (1) furrow irrigation and sidedress fertilizer injection (conventional system) and (2) drip irrigation, reduced tillage, and fertigation (integrated system). Nitrous oxide emissions were monitored for seven to ten days following major events of cultivation, irrigation, fertilization, harvest, and winter precipitations. Total weighted growing season emissions (15 March–1 November 2010) were 2.01±0.19kgN2O-Nha−1 and 0.58±0.06kgN2O-Nha−1 in the conventional and integrated systems, respectively. The highest conventional system N2O emission episodes resulted from fertilization plus irrigation events and the first fall precipitation. In the integrated system, the highest N2O fluxes occurred following harvest and the first fall precipitation. Soil chemical and physical properties of soil moisture, inorganic nitrogen (N), and dissolved organic carbon (DOC) were low and less spatially variable in the integrated system. Used as an index of substrate availability, soil ammonium (NH4+) and nitrate (NO3−) exposures were significantly lower in the integrated system. Of great importance is that the drip irrigation water and fertilizer management of the integrated system also increased crop yield (119Mgha−1 vs. 78Mgha−1), highlighting the potential for decreasing N2O emissions while simultaneously improving the use of water and fertilizer for plant production.

Water Energy Nexus at a California Tomato Processing Facility

A Water Energy Nexus assessment at a California tomato processing facility reveals opportunities to advance corporate sustainability objectives by enhancing thermal energy efficiency, reducing electricity consumption, and conserving ground water resources. The adoption of energy efficiency measures and water recovery recommendations will deliver economic benefits from reduced energy costs, lower air pollution emissions, preservation of ground water resources, and reduced discharge of waste water to the environment. A base line is developed to account for the water energy intensity of processing tomatoes at this facility. This base line will be used to compare the economic and environmental benefits of adopting resource efficiency measures. Food companies that adopt tangible resource conservation and efficiency improvements can attribute sustainability principles to long term water and energy conservation investments.

Evolution of Conservation Tillage Systems for Processing Tomato in California’s Central Valley

Traditional processing tomato (Solanum lycopersicum) production in California’s Central Valley relies heavily on tillage to produce high yields. However, recent research and farm innovation have produced a variety of conservation tillage (CT) management alternatives that cut costs, reduce soil disturbance, and produce fewer emissions. A 12-year study in Five Points, CA, demonstrated that CT methods reduced tractor passes by 40%, lowered tillage costs by ≈$80 per acre in 2011 dollars, and achieved comparable yields as standard tillage (ST) methods. As comparable yield performance and net profitability are further demonstrated, an array of CT systems will become increasingly attractive to producers and more common in Central Valley tomato growing areas.

Distinct influence of filter strips on acute and chronic pesticide aquatic environmental exposure assessments across U.S. EPA scenarios

Vegetative filter strips (VFS) are proposed for protection of receiving water bodies and aquatic organisms from pesticides in runoff, but there is debate regarding the efficiency and filter size requirements. This debate is largely due to the belief that no quantitative methodology exists for predicting runoff buffer efficiency when conducting acute and/or chronic environmental exposure assessments. Previous research has proposed a modeling approach that links the U.S. Environmental Protection Agency’s (EPA’s) PRZM/EXAMS with a well-tested process-based model for VFS (VFSMOD). In this research, we apply the modeling framework to determine (1) the most important input factors for quantifying mass reductions of pesticides by VFS in aquatic exposure assessments relative to three distinct U.S. EPA scenarios encompassing a wide range of conditions; (2) the expected range in percent reductions in acute and chronic estimated environmental concentrations (EECs); and (3) the differential influence of VFS when conducting acute versus chronic exposure assessments. This research utilized three, 30-yr U.S. EPA scenarios: Illinois corn, California tomato, and Oregon wheat. A global sensitivity analysis (GSA) method identified the most important input factors based on discrete uniform probability distributions for five input factors: VFS length (VL), organic-carbon sorption coefficient (Koc), half-lives in both water and soil phases, and application timing. For percent reductions in acute and chronic EECs, VL and application timing were consistently the most important input factors independent of EPA scenario. The potential ranges in acute and chronic EECs varied as a function of EPA scenario and application timing. Reductions in acute EECs were typically less than percent reductions in chronic EECs because acute exposure was driven primarily by large individual rainfall and runon events. Importantly, generic specification of VFS design characteristics equal across scenarios should be avoided. The revised pesticide assessment modeling framework offers the ability to elucidate the complex and non-linear relationships that can inform targeted VFS design specifications.

Use of vegetated agricultural drainage ditches to decrease pesticide transport from tomato and alfalfa fields in California, USA

Irrigation and storm water runoff from agricultural fields has the potential to cause impairment to downstream aquatic receiving systems. Over the last several years, scientists have discovered the benefit of using edge-of-field practices, such as vegetated agricultural drainage ditches, in the mitigation of pesticides and sediment. After demonstrating this practice's feasibility in California, field trials were initiated to document irrigation runoff pesticide mitigation in California alfalfa and tomato fields. In the alfalfa field, chlorpyrifos concentration was decreased by 20% from the inflow to the ditch outflow. Thirty-two percent of the measured chlorpyrifos mass was associated with ditch plant material. In the tomato field, permethrin concentration was decreased by 67% and there was a 35% reduction in suspended sediment concentration from inflow to the ditch outflow. When surface water was not present in the ditch systems, the sediment was a significant repository for pesticides. Based on the field trials, vegetated agricultural drainage ditches can be successfully used as part of a suite of management practices to reduce pesticide and sediment runoff into aquatic receiving systems.

Use of vegetated agricultural drainage ditches to decrease toxicity of irrigation runoff from tomato and alfalfa fields in California, USA

The current study investigated the potential of vegetated drainage ditches for mitigating the impact of agricultural irrigation runoff on downstream aquatic ecosystems. Water column toxicity to larval fathead minnow (Pimephales promelas),and the amphipod Hyalella azteca was measured for 12 h or less at the ditch inflow and outflow, using custom-built in situ exposure systems. In addition, water and sediment samples were subject to standard toxicity tests with Ceriodaphnia dubia and H. azteca, respectively. No acute toxicity to larval fathead minnow was observed; however, runoff was highly toxic to invertebrates. Passage through a 389- to 402-m section of vegetated ditch had a mitigating effect and reduced toxicity to some degree. However, runoff from an alfalfa field treated with chlorpyrifos remained highly toxic to both invertebrate species, and runoff from a tomato field treated with permethrin remained highly toxic to H. azteca after passage through the ditch. Predicted toxic units calculated from insecticide concentrations in runoff and 96-h median lethal concentration (LC50) values generally agreed with C. dubia toxicity measured in the laboratory but significantly underestimated in situ toxicity to H. azteca. Sediments collected near the ditch outflow were toxic to H. azteca. Results from the current study demonstrate that experimental vegetated ditches were unable to eliminate the risk of irrigation runoff to aquatic ecosystems. In addition, protective measures based on chemical concentrations or laboratory toxicity tests with C. dubia do not ensure adequate protection of aquatic ecosystems from pyrethroid-associated toxicity.

Population analyses of the vascular plant pathogen Verticillium dahliae detect recombination and transcontinental gene flow

The fungal pathogen Verticillium dahliae has resulted in significant losses in numerous crops in coastal California, but lettuce remained unaffected until the mid-1990s. Since then outbreaks have decimated entire fields, but the causes of this sudden susceptibility of lettuce remain elusive. The population structure of V. dahliae isolated from coastal California (n=123) was investigated with 22 microsatellite markers, and compared with strains from tomato in central California (n=60), spinach seed imported from Washington State and Northern Europe (n=43), and ornamentals from Wisconsin (n=17). No significant differentiation was measured among hosts in coastal California or with the spinach and Wisconsin ornamental sampling groups. In contrast, the tomato sampling group was significantly differentiated. Significant gene flow was measured among the various geographic and host sampling groups, with the exception of tomato. Evidence of recombination in V. dahliae was identified through gametic disequilibrium and an exceedingly high genotypic diversity. The high incidence of V. dahliae in spinach seed and high planting density of the crop are sources of recurrent gene flow into coastal California, and may be associated with the recent outbreaks in lettuce.

Characterization of Curtoviruses Associated with Curly Top Disease of Tomato in California and Monitoring for These Viruses in Beet Leafhoppers.

Curly top disease is caused by a complex of curtoviruses (family Geminiviridae), and it continues to plague tomato production in California. To better understand the etiology of curly top of tomatoes in California, polymerase chain reaction (PCR)-based methods were developed and used to characterize the curtoviruses involved, and to monitor for these viruses in the beet leafhopper vector, Circulifer tenellus. From 2002 to 2008, 86 processing and fresh market tomato fields in the Central Valley of California were surveyed for the incidence of curly top symptoms. Representative samples with curly top symptoms were collected from the surveyed fields, as well as from another 24 fields. The incidence of curly top symptoms in most fields ranged from trace (<1%) to low (1 to 5%); however, in 2002, 2003, and 2008, some fields had medium (5 to 20%) or high (>20%) incidences. PCR with general and species-specific primers was used to establish that the predominant species associated with tomato curly top disease were Beet mild curly top virus (BMCTV) and, to a lesser extent, Beet severe curly top virus (BSCTV). The incidence, relative amount, and species of curly top virus in leafhoppers, collected at monthly intervals by the California Department of Food and Agriculture (CDFA) personnel during 2003 to 2008, was also determined. The predominant species detected were BMCTV and BSCTV. The highest incidences of curly top in tomato fields were associated with high populations of leafhoppers (e.g., in 2003 when populations were two times greater than average) having high incidences and levels of curly top virus early in the growing seasons (e.g., March to May 2003 and 2008). Detection of curly top virus in leafhoppers early in the growing season was consistent with acquisition of virus from reservoir hosts in the foothills. However, continued detection of curly top virus in leafhoppers throughout the growing season and development of curly top in late-planted fresh market tomatoes were consistent with the presence of inoculum sources (e.g., weeds or crop plants) in the agricultural areas of the Central Valley. Geographical locations or "hotspots" having higher proportions of curly top virus-positive leafhoppers were identified, which may reveal areas having high concentrations of curly top virus reservoir hosts. The application of these molecular tools has provided new insight into curly top of tomato in California, and may lead to improved curly top management.

An Outbreak of a Necrosis Disease of Tomato in California in 2008 was Caused by a New Ilarvirus Species Related to Parietaria mottle virus.

During the 2008 early-summer growing season, virus-like necrosis symptoms, most similar to those induced by Tobacco streak virus (TSV), were observed in leaves, stems, and petioles of processing tomato plants in the Central Valley of California. Symptoms were observed in numerous fields in Merced, San Joaquin, and Yolo counties, though the incidence of the disease in most fields was not high (not more than 5% but over 20% in some areas). Antibody-based tests of representative samples of the disease for infection with Tomato spotted wilt virus, TSV, and Tomato apex necrosis virus, which cause similar symptoms, were negative. A putative virus-like agent was sap- and graft-transmitted to tomato plants and induced necrotic spots in leaves and stem and petiole necrosis symptoms that were similar to those observed in the field. Eventually, these plants recovered from these symptoms. In sap-transmission experiments, the virus-like agent induced systemic symptoms in Chenopodium quinoa and C. amaranticolor (stunted growth and leaf curl and necrosis), Nicotiana benthamiana (necrotic leaf and stem lesions), N. tabacum cvs. Havana and Turkish (stunted growth and necrotic etching and ringspots followed by recovery for cv. Havana but not for cv. Turkish), and Datura stramonium (mild mottle and ringspots in newly emerged leaves followed by recovery); no symptoms were observed in inoculated common bean (cv. Topcrop), pumpkin (cv. Small Sugar), pepper, and N. glutinosa plants. Virus minipurification was performed with leaves from noninfected and infected D. stramonium plants, and polyacrylamide gel electrophoresis analyses revealed a protein band of ~29 kDa in infected but not noninfected plants. This protein was purified and subjected to liquid chromatography-mass/mass spectrometry analysis. Four peptides, obtained from the trypsin-digested protein, each had the highest match (score of 118) with the capsid protein (CP) of Parietaria mottle virus (PMoV), an ilarvirus that induces leaf and stem necrosis in tomatoes in Europe (1). Using sequences of PMoV and other ilarviruses, a single primer was designed from the 3' nontranslated region and paired with primers designed from conserved regions of ilarvirus RNAs 1, 2, and 3. In reverse transcription-PCR analyses, these primer pairs directed the amplification of the expected-sized fragments for ilarvirus RNAs 1, 2, and 3 from RNA extracts prepared from leaves with the unusual necrosis symptoms. Sequence analyses confirmed these were ilarvirus fragments. Partial RNA 1, 2, and 3 sequences were 81, 84, and 82% identical, respectively, with those of PMoV and 80, 77, and 69% identical, respectively, with those of TSV. The amino acid sequence of the CP gene (GenBank Accession No. FJ236810) was 86 and 61% identical to those of PMoV and TSV, respectively. Together, these results indicate the necrosis disease of tomato is caused by a new ilarvirus species, tentatively named Tomato necrotic spot virus, although further studies are needed to confirm this. The mode of transmission of this new ilarvirus to tomatoes in the field is unknown, but it may involve thrips feeding on infected pollen, a known method of transmission for TSV (2).