Research in the Ullman Lab

Ullman Laboratory Staff

Sandra Kelley, Staff Research Associate
mailto:skkelley@ucdavis.edu

     Sandra is the operations manager for the Ullman Laboratory and conducts research on aphid transmission of citrus tristeza virus. She is the Chair of the departmental Greenhouse Use Committee and serves on the College of Agriculture and Environmental Sciences Greenhouse Committee. Sandra has her M.S. in Plant Pest Protection and Management from the University of California at Davis.

---

Ashley Cameron, Post Graduate Researcher
ancameron@ucdavis.edu

     Ashley is investigation the efficacy of induced resistance in controlling thrips and tospoviruses. Ashley has her B.S. in Genetics from University of California at Davis.

---

Amal Salem, Postdoctoral Researcher
ancameron@ucdavis.edu

     Amal is investigating the role of aphid transmission in the genetic diversity and transmissibility of citrus tristeza virus. Amal has her Ph.D. from Cairo University.

 

Ullman Laboratory Mission

     The research focus in the Ullman laboratory is on insect/virus/plant interactions and development of management strategies for insect-transmitted plant pathogens. Dr. Ullman was hired to conduct research in this area with the specific mandate of fostering multidisciplinary, cross divisional collaborative efforts. Consequently, the lab has many collaborations that are national and international in scope. The specific goals of the Ullman research program are to expand knowledge of insect vector/pathogen interactions on a cellular level, to determine how these interactions influence epidemiology and management of diseases caused by insect transmitted pathogens and to understand mechanisms of host plant resistance against insect vectors or their transmission of viruses. The research questions addressed have necessitated conducting investigations with a variety of insect vector species, including thrips, aphids, leafhoppers, whiteflies and mealybugs, and, several plant virus systems tospoviruses, citrus tristeza virus, potato leafroll virus, curlytop virus). The research approaches have varied from very basic studies in the laboratory to more applied investigations in the field. In general, the short-term goal of these investigations has been to elucidate basic information that is currently lacking regarding the inter-relationships between insect vectors, plants and plant pathogenic viruses. The long-term goal of the program is to translate advances in understanding of these relationships into technologies or methodologies that can be applied as novel strategies for preventing epidemics of insect transmitted pathogens.

Current Research Projects

• Can elicitors of induced resistance be used to control thrips and tospoviruses in ornamental plants? (Primary Collaborator: Karen Robb, University of California Cooperative Extension Service, San Diego County)

     Thrips and the tospoviruses they transmit remain one of the most severe and intractable control problems that ornamental growers face across the nation. In California, epidemics have been especially severe in chrysanthemums and a relatively new crop, lisianthus. Plantings of lisianthus have grown tremendously in the state and growers have serious problems with tospovirus infection. Thrips quickly gain resistance to most insecticides and conditions associated with the Food Quality Protection Act make new strategies for their control even more important. The only methods for controlling tospoviruses are those that revolve around prevention. Once a plant has been infected there is no cure. New tospoviruses are emerging worldwide, many of them are transmitted by the western flower thrips and infect ornamentals (Ullman et al. 2002, see publication list).
     Induced resistance involves plant-mediated changes associated with initial attack by herbivores and pathogens that negatively influence subsequent attackers. The jasmonate pathway (i.e., the octadecanoid pathway) and the salicylate pathway (conditioning systemic acquired resistance, SAR) are two of the biochemical response mechanisms that can be triggered by various attackers. The components of these pathways, jasmonic and salicylic acids (JA and SA, respectively), act as signals that trigger naturally occurring chemical responses that protect the plant from insect and pathogen invaders. We have been exploring the use of JA and SA elicitors as tools for controlling thrips and tospoviruses. Our data shows a wide range of responses, depending on the plant species and use of wetting and spreading agents. Our findings show that with correct application thrips can be dramatically reduced. We do not yet have complete data for reduction of tospoviruses. We were concerned that possible cross-talk or negative interactions might occur between these pathways and tested this possibility. Elicitation of both pathways did not negatively impact thrips control, although plant defense against some other pests was reduced (Thaler et al. 2002, see publication list). We are currently evaluating two currently registered products with active ingredients that stimulate the jasmonate and salicylate plant pathways for defense.
     Bion® (marketed in Europe) or Actigard® (marketed in the USA by Syngenta) has the active ingredient benzo [1,2,3] thiadizaole-7-carbothioic acid-S-methyl ester or benzothiadiazole (BTH). BTH acts like SA and elicits systemic acquired resistance (the salicylate pathway). It is best tested for control of bacteria and fungi. Messenger (Eden Bioscience Corporation) has the active ingredient harpin (a protein derived from the bacteria Erwinia amylovora). Harpin triggers a cascade of responses that stimulate the salicylate pathway AND the jasmonate pathway. It has also been shown to stimulate nutrient uptake and photosynthesis. When it is effective, the response is initiated within 10 minutes of treatment and depending on the plant species, may continue for several weeks. We will test these products alone and in combination as tools for protecting chrysanthemums and lisianthus against thrips and tospoviruses. We are also testing a JA analog, coronalan. To our knowledge, we are the first to test these products in ornamental cropping systems.

Objectives

• To test the feasibility and optimum conditions for controlling thrips and tospoviruses in chrysanthemums and lisianthus with compounds eliciting induced plant resistance: Bion® /Actigard®, Messenger® and Coronalan.
• Assess efficacy of each product alone for thrips control and tospovirus prevention (laboratory and field).
• Assess efficacy of the products used in combination for thrips control and tospovirus prevention (laboratory and field).
• Determine the optimum timing and methodology for application (laboratory and field).
• Assess impacts on plant growth and yield.
Laboratory assays are underway and field experiments will be conducted in autumn 2002 with grower cooperators in San Diego, California.

THIS RESEARCH HAS BEEN FUNDED BY THE AMERICAN FLORAL ENDOWMENT, THE CALIFORNIA CUT FLOWER COMMISSION (KEE KITYAMA RESEARCH FOUNDATION), BARD AND PRIVATE DONATIONS BY MELLANO AND CO.
• Identification of a Thrips Receptor for Tomato Spotted Wilt Virus (Bunyaviridae, Tospovirus). (Primary Collaborator: Thomas L. German, University of Wisconsin)

     Tomato spotted wilt tospovirus (TSWV) and related tospoviruses are transmitted by several species of thrips and cause epidemics in many crops worldwide, infecting more than 600 plant species. In spite of the serious nature of TSWV epidemics and the profound need for novel control measures, basic information about vector/virus interactions that could lead to development of these measures is scant. We propose that by understanding the receptor-ligand interactions that mediate virus acquisition, it will be possible to design strategies to prevent acquisition by blocking virus attachment in the vector, or to engineer the ligand for use as a tool to deliver novel toxins to thrips. Recently, we have documented that the membrane glycoproteins (GPs) of TSWV selectively bind a 50 kDa protein present in extracts from whole insects and dissected midguts of the TSWV vector, the western flower thrips (WFT). The 50 kDa protein was shown to be abundant in larvae, the developmental stage known to acquire TSWV, but absent or present in low quantities in adults, which are refractory to acquisition of the virus. Anti-idiotypic antibodies that mimic the TSWV GPs specifically bound this protein in western blots and labeled midgut membranes of larval WFT. The 50 kDa protein was not detected in nonvector insects, nor did TSWV proteins other than the GPs bind thrips vector proteins. Based on our earlier documentation of events in virus acquisition by thrips and these recent findings, we hypothesize that the TSWV GPs, which are embedded in the viral membrane, serve as attachment proteins (ligands) that interact with cellular receptor(s) in the WFT midgut to mediate virus acquisition and that the 50 kDa thrips protein we identified serves as one such cellular receptor or a component thereof. This hypothesis is consistent with mechanisms of virus acquisition described for mosquito transmitted membrane-bound viruses of vertebrates. Our specific objectives are to: (1) Identify and characterize the cellular receptor(s) present in the thrips midgut, (2) Identify and clone the open reading frame(s) encoding the thrips cellular receptor protein(s), and, (3) Establish the relationship of occurrence and localization of the cellular receptor(s) to thrips development and vector competency. The research benefits from an interdisciplinary approach in which all the PI laboratories have complimentary expertise and infrastructure for conducting the needed experiments.

THIS RESEARCH HAS BEEN FUNDED BY BARD AND BY USDA COMPETITIVE GRANTS PROGRAMS.

• Aphid Transmission Of Citrus Tristeza Virus And How It Determines Genetic Variability And Symptom Expression In The San Joaquin Valley (Primary Collaborators: Elizabeth Grafton-Cardwell, Bryce Falk,Dave Gumpf, MaryLou Polek, Amal Salem, Hany Sheta, Luis Rubio, Ray Yokomi)

     Citrus tristeza virus (CTV) (Closteroviridae, Closterovirus) is transmitted by aphids and can be found at low levels in many locations in the San Joaquin Valley (SJV) and worldwide in every location that grows citrus. Molecular characterization revealed that many SJV CTV isolates are composed of virion populations that can be genetically diverse, even within a single tree (Falk et al. 2000). Molecular diversity in citrus tristeza isolates from California. Virus Genes 21:139-145). Biological characterization of CTV isolates using a range of plant host species shows that SJV CTV isolates also vary relative to the appearance and severity of symptoms that they cause (Polek and Gumpf, unpublished). Most SJV CTV isolates are mild when compared to those found in other countries.
     We have shown that A. gossypii transmission from CTV-infected citrus in SJV commercial orchards resulted in infections that were genetically different from the parent (source) tree in the orchard (Sheta, Ullman and Falk, unpublished). When A. gossypii and A. spiraecola transmitted CTV from the same parent tree, both aphid species could transmit the same or different members of the virus population (Salem, Ullman and Falk, unpublished). Biocharacterization of some of these isolates indicate that aphid transmission some times results in a symptom phenotype (severity rating) that is higher than the parent tree source. Although the virus does not replicate in the aphid (it is semipersistently transmitted), passage by the aphid results in dramatic changes to the virus population structure. In some cases, genetic diversity was dramatically narrowed. In others, and this is apparently more common, genetic diversity of the virus increased after aphid passage. These are the first data to provide quantitative genetic evidence that aphids transmit particular isolates selectively and to reveal their impact on virus population structure and genetic diversity. We are embarking on experiments to determine how brown citrus aphid transmission will impact the population structure of California isolates. This is an important concern for the citrus industry in California and the results will help predict the potential impact of the brown citrus aphid in CTV epidemics in the San Joaquin Valley.

THIS RESEARCH HAS BEEN FUNDED BY THE CITRUS RESEARCH BOARD, THE CALIFORNIA COALITION FOR TRISTEZA RESEARCH AND USDA-CSREES SPECIAL RESEARCH PROGRAMS.