MANAGEMENT AND BIOLOGY OF ARTHROPOD PESTS AND ARTHROPOD-BORNE PLANT PATHOGENS

Control of arthropods that transmit pathogens is arguably one of the biggest challenges to human health and agriculture. Many serious plant and animal pathogens are dependent upon arthropod vectors for transmission between hosts. Nearly all arthropod-transmitted animal pathogens are internalized and circulate in their insect vectors, while plant pathogens are divided between those that circulate in their vectors and those that are carried on the cuticle linings of mouthparts and foreguts. The mechanisms of circulative transmission are only beginning to be dissected, but already commonalities among transmission of both circulative plant and animal pathogens have been discovered. Our experimental systems offer innovative approaches to manage circulative- transmitted plant pathogens that have been recalcitrant to the development of host resistance and for which the economic and environmental costs of vector control has been prohibitive, unsustainable and/or ineffective. Scientists' incomplete understanding of interactions among insect vectors, plant pathogens and plant hosts limits the development of new tools to block or interfere with pathogen transmission by insects in the field. We address this problem by attempting to discover genes and products that mediate the associations among insect vectors, circulative plant pathogens and plant hosts. The new technologies and knowledge are expected to be extended and applied to the study of other circulative pathogens and will greatly impact growers, industry stakeholders, and other research communities. The project will also focus on maintaining the extensive ARS Collection of Entomopathogenic Fungal Cultures (ARSEF). ARSEF contains 12,500 isolates representing 700 fungal taxa from 1,300 hosts and 2,400 locations worldwide, and will be managed to ensure ongoing accession, preservation, identification, and distribution of fungal isolates for development and deployment as biocontrol agents and for research purposes. The ARSEF collection also plays a central role in revising taxonomies of fungi using the state-of-the-art systematic methods. Final Report. New Project under OSQR review. Objective 1: ARSEF continues to provide the following services: 1) fungal culture deposition; 2) distribution; and 3) identification. ARSEF accessioned 199 new fungal isolates. 187 isolates were shipped in response to 36 requests from non-profit institutions in the US and abroad. ARSEF provided fungal identification services by examining morphological characters and/or by sequencing of diagnostic loci, oftentimes requiring establishment of pure fungal cultures. A subset of deposits are being processed for identification to genus or species via DNA sequencing. Data and services are publicly available on the ARSEF website. Catalogs of common fungal genus or insect host order have been compiled for the ARSEF website. Research focuses on fungal pathogens of Diaphorina citri, the Asian citrus psyllid, and vector of citrus greening disease, whitefly Biotype B, mosquitoes and the sugarcane aphid. A new agreement between ARSEF and the Agricultural Genetic Resources Preservation Research was approved to back up critical fungal strains. Sub-Objective 2.1: Identification of pathogen, host, and vector components that regulate uptake and transmission of pathogens by sap- sucking insects. Work focused on aphids that transmit the circulative, plant pathogenic poleroviruses. ARS scientists discovered that the P0 protein from potato leafroll virus (PLRV), a plant virus that is spread by the green peach aphid, suppresses the aphid immune system. The weakened aphid immune system makes the aphid more susceptible to an aphid- infecting virus, called a densovirus. Densoviruses induce the formation of winged aphids, which would enable the aphid to move plant viruses long distances. In host plants, P0 suppresses the silencing machinery by marking the protein argonaut 1 (AGO1) for degradation. P0 forms an E3 ubiquitin ligase complex in planta that ubiquitinates AGO1. Current research is focused on whether E3 ubiquitin ligase activity is involved in the effect of P0 on the aphid antiviral immune system. ARS scientists have shown that P0 can exert its effect on the aphid antiviral immune system in the context of the plant host. It is not known if P0 signals indirectly through the plant and whether the plant is required for this effect. Ongoing experiments are testing between the hypotheses as to whether P0 exerts its effect directly on the aphid or indirectly via the plant. Research has advanced on the viral structural protein that regulates aphid transmission. Data show that the PLRV structural protein that regulates aphid transmission forms a particular structure that is conserved among different poleroviruses, suggesting a conserved function in virus transmission by aphids. Mutant forms of the protein are lethal to aphids when delivered by an artificial diet. Research is focused on developing and optimizing transmission blocking strategies using this form of the virus structural protein, characterizing aphid proteins that bind to this protein and visualization of the virus at the atomic level. This work will generate new fundamental knowledge about aphid transmission of poleroviruses and help our team to optimize a strategy to block virus transmission to transfer to growers. An invasive polerovirus, Cotton leafroll dwarf virus (CLRDV) is an emerging threat to cotton grown in the United States. ARS scientists in Ithaca, NY are collaborating with ARS scientists in Stoneville, MS to translate the Potato leafroll virus management strategies to the new emerging cotton polerovirus. While there is a wealth of data on polerovirus biology as a result of studies on PLRV and the related yellow dwarf viruses, very little is known about the biology of CLRDV, its interactions with host cotton varieties and transmission by the cotton aphid, Aphis gossypii. The impact of this virus on cotton production is currently unknown, and management strategies are nonexistent. Together with a Cornell PhD student, the Lead Scientist traveled to the ARS location in Stoneville, MS to collect A. gossypii genotypes from cotton. Over 40 aphids were collected from various sites in Mississippi and Alabama. Two A. gossypii clones survived and are reproducing parthenogenetically under lab conditions. These clones will have their genomes sequenced next year as a part of the Ag100 Pests Project. Research is focusing on determining whether plants collected from the field are infected with CLRDV for aphid transmission studies and generation of a CLRDV infectious clone for laboratory research. Work on this sub-objective also focused the bacterium associated with citrus greening in the USA, Candidatus Liberibacter asiaticus (CLas). Liberibacter crescens is the only axenically cultured Liberibacter and serves as a surrogate for functional genomic studies of the pathogenic â¿¿Ca. Liberibacterâ¿