Progress 09/01/08 to 08/31/10

Outputs
OUTPUTS: This interdisciplinary (plant virology, entomology, horticulture, breeding), multi-state (AZ, CA) project addressed the introduction of a new, exotic virus of melon crops. The objectives were to determine the distribution of the whitefly-transmitted Cucurbit yellow stunting disorder virus (CYSDV), clarify the disease cycle, identify over-seasoning hosts, and develop chemical and cultural control management practices to reduce disease pressure. Twenty melon varieties and 100 melon germplasm were screened for CYSDV resistance. To determine potential reservoir hosts 176 weed and crop samples were collected from virus-affected areas (Sept 2008-Oct 2009). The CYSDV host range was determined by analyzing samples using RT-PCR and/or qPCR detection. CYSDV was detected in plant species within and outside of the Cucurbitaceae, and seven additional families containing virus hosts were identified. Species confirmed as virus hosts were malvaceous (3 Malva spp.; alkali mallow) and other weeds: morning glory, Physalis wrightii, velvetleaf, silverleaf nightshade, lambsquarters, pigweed, London rocket, and five hook bassia; cultivated hosts: alfalfa, bean, canteloupe, honeydew, cassaba, cucumber, watermelon, bean, lettuce (romaine), Hibiscus, and papaya. CYSDV was detectable by RT-PCR and qPCR in some hosts, while in others (mostly asymptomatic) detection was possible only by qPCR. Whitefly (B biotype) transmission experiments using melon as the indicator plant revealed differences in transmission efficiency. Studies confirmed that whiteflies could acquire CYSDV from lettuce (Lactuca sativa), buffalo gourd (Cucurbita foetidissima), alkali mallow (Sida hederacea), and ground cherry (Physalis wrightii) and transmit it to melon plants. Studies are proposed to examine the quantitative relationship between virus titer, symptom severity, and whitefly vector transmission efficiency. Geospatial analysis of 105 whitefly trap counts and melon fields (Yuma, AZ) was conducted. The goal of establishing a regional education and management program for AZ and CA producers to encourage implementation of 'best' practices was achieved, including a demonstration that a host free summer period abates early season CYSDV outbreaks and virus over-seasoning that leads to fall crop infection, and the dissemination of new knowledge about virus biology and whitefly dispersal patterns in southern Arizona (which can influence disease spread in AZ, CA and Sonora), resulted in increased regional awareness and understanding of CYSDV epidemiology. Row cover experiments and insecticide regimes duplicated in Yuma and Imperial Valley demonstrated new approaches for reducing exposure of melons to whitefly early in the growing season. Promising melon germplasm, PI 313970 and TGR-1551, show CYSDV tolerance and were incorporated in the USDA-ARS, Salinas melon breeding program. Data dissemination was carried out regularly. Collaborators presented research updates at monthly Task Force meetings (AZ) and/or scheduled CA Melon Board meetings (CA), and formal workshops organized by Nolte and Natwick. The combined team effort produced new information relevant to CYSDV and whitefly vector management. PARTICIPANTS: Collaborators were: William M. Wintermantel, Virologist, Vector biologist; USDA-ARS, 1636 East Alisal Street, Salinas, CA 93905; bill.wintermantel@ars.usda.gov Kurt Nolte; Director; Extension-Vegetable crops; Yuma County Cooperative Extension, 2200 W. 28th St. Suite 102. Yuma, AZ 85364; knolte@cals.AZ.edu Stacey Bealmear; Assistant Agent, Urban Horticulture, Yuma County Cooperative Extension, 2200 W. 28th St. Suite 102. Yuma, AZ 85364; staceyb@cals.AZ.edu John Palumbo, Entomology, University of Arizona, Yuma Agriculture Center, Yuma, AZ 85364 jpalumbo@ag.arizona.edu Robert Gilbertson, Virologist/Plant Pathologist, Department of Plant Pathology, 1 Shields Ave.; The University of CA, Davis, CA 95616; rlgilbertson@ucdavis.edu Eric Natwick, Extension Agronomist; Entomology; University of CA Cooperative Extension, 1050 East Holton Road, Holtville, CA 92250; etnatwick@ucdavis.edu TARGET AUDIENCES: Target audiences in CA and AZ were producers, pesticide applicators, county agents, seed companies, CA Melon Board, AZ CYSDV-Melon Task Force. Target audiences also were cucurbit (cucumber, melon, squash, watermelon) producers, field managers, entomologists and pathologists (University of Sonora, Hermosillo), and the producers organizations in Caborca, Hermosillo, and Obregon, Sonora where cucurbits are grown commercially. PROJECT MODIFICATIONS: Not relevant to this project.

Impacts
Understanding the virus host range and distribution in the Yuma-Imperial Valley interface (together with data from Sonora) enabled us to conclude that the host range of the virus was much more extensive than anticipated. Results of field sampling to determine the host range and study the disease epidemiology indicated that a number of alfalfa fields are infected with CYSDV, however, fortunately, it seems to be a relatively poor source of the virus for whitefly transmission. Producers and/or their field managers increased sanitation practices by removing weeds nearby fields and participated in a host free summer period to reduce viral inoculum prior to fall planting. Additionally, CYSDV was shown to have established widely throughout the region, indicating continuation of judicious practices would be required to sustain melon production in AZ and CA. Monitoring whitefly populations at selected locations in the Yuma Valley and construction of weekly whitefly density maps, provided new insights into yearly migration patterns and how they are influenced by the intricacy of the area. This was particularly evident during the cucurbit host free period of July 5th- August 5th. Following the cucurbit host free period, significant regional reduction in whitefly numbers was observed, yet the City of Yuma and Yuma Mesa areas increased (YM) or maintained (CoY) whitefly numbers. It appeared that whitefly dispersal during periods of crop host removal significantly affected other crops within a geographic area by increasing new infestations. And, the specific directional whitefly counts revealed that whitefly entered the adjacent urban setting from the West countering the notion that urban migration of whitefly to agricultural areas. Overall, measures were implemented to more effectively manage the whitefly vector (timing of insecticides at first sighting of whitefly dispersal to melon fields, use of new insecticides to kill immature and adult whiteflies, better sanitation practices involving weed hosts and volunteer melon seedlings in the off-seasons (after spring and fall crops), implementation of a modified-host free period (when possible based on market demand for the product). Certain melon varieties identified by monitoring yield loss in relation to symptom severity are now grown as preferred varieties in the absence of durable resistance. These collective measures have minimized losses compared to those experienced in the two years following the initial outbreak, have sustained melon production for the region, and have slowed the spread of CYSDV to unaffected areas. Germplasm screening and subsequent crosses with promising materials identified in the USDA and other worldwide collections identified several promising accessions that have been integrated into the regional melon improvement breeding program.

Publications

• Abstract: Wintermantel, W.M., Gilbertson, R.L., Brown, J.K., and Natwick, E.T. (2010). Emergence and establishment of Cucurbit yellow stunting disorder virus in California and Arizona poses a threat to desert melon production. APS Meeting, Nashville TN August 2010 (poster).
• Website: (2010) UC IPM On-Line: Pest Management Guidelines: Cucurbits- Cucurbit Yellow Stunting Disorder UC ANR Publication 3445 http://www.ipm.ucdavis.edu/PMG/r116100211.html

Progress 09/01/08 to 08/31/09

Outputs
OUTPUTS: 1. Developed and optimized a real-time, quantitative PCR and RT-PCR assays for CYSDV detection in cultivated and wild plant hosts in Arizona and California. 2. Based on sampling during 2007-2009, the known distribution of the introduced CYSDV is presently four counties in Arizona and two counties in California where the majority of melon crops are produced in the SW deserts of the US. The virus also persists south of us in Sonora and probably other states on the west coast of Mexico, therefore southerly sources of whiteflies and virus persist as well. 3. CYSDV has become persistent in the lowland deserts of Arizona and California, and has been a problem each year since its introduction in 2006 indicating additional work will be required to manage this new disease together with already existing whitefly-transmitted viruses that are native to the region. 4. CYSDV has a broader than expected host range. In addition to cucurbit species that were initially thought to be the only hosts of CYSDV, a number of confirmed and additional suspect plant species in at least five different families have been identified using RT-PCR and qPCR assays. Follow-on work is in progress to confirm non-cucurbit hosts through transmission studies and molecular confirmation (See Tables 1,2). 5. Produced the first whitefly density and distirbution maps for Yuma County (Nolte and Palumbo) to aid in understanding short and long-term dispersal patterns within the county and surrounding areas. Areas near the Colorado River and the UA Experimental plots have high densities in the spring and fall seasons. Cotton is a major source of late summer whiteflies for fall melon crops. It may be that whiteflies migrate south to north in the Spring season and that local overwintering populations together contribute to the Spring population. 6. Research-based information regarding the most effective chemistries including row cover strategies for whitefly control, in keeping with minimizing development of resistance. CA trials were tailored to local planting times, wihtefly pressures, varieties grown in Holtvillle but information is applicable to Yuma and La Paz counties as well. 7. Progress toward identifying germplasm with possible resistance genes that can be introgressed into cultivated varieties through the USDA- Salinas melon breeding program. 8. Educational materials and regular updates and workshops have been an integral component of the project. These interactions have contributed to and producer/field manager participation, and have proven tremendously useful to rapid information dissemination and the overall problem-solving and progress toward management that is knowledge-based. PARTICIPANTS: Principal Investigator: Judith K. Brown, Univ. of Arizona, Tucson, AZ; jkbrown@ag.arizona.edu Cooperating Personnel Robert L. Gilbertson, University of California-Davis, Davis, CA 95616; rlgilbertson@ucdavis.edu James D. McCreight, USDA-ARS, Salinas, CA; jim.mccreight@ars.usda.gov Eric T. Natwick, UCCE-Imperial County, El Centro, CA; etnatwick@ucdavis.edu William M. Wintermantel, USDA-ARS, Salinas, CA; bill.wintermantel@ars.usda.gov Erin Taylor and Kurt Nolte, Cooperative Extension, The University of Arizona; etaylor@ag.arizona.edu; knolte@ag.arizona.edu Locations Department of Plant Pathology, University of California-Davis Department of Plant Sciences, University of Arizona-Tucson University of California Desert Research and Extension Center, El Centro, CA USDA-ARS, 1636 East Alisal Street, Salinas, CA Maricopa-Pinal Counties; Yuma County; The University of Arizona-Coop Ext. TARGET AUDIENCES: The proposed research and survyes, and follow-up workshops were coordinated with Area Extension personnel in AZ and CA to achieve initial steps to: establish CYSDV detection systems in AZ (RT-PCR and qPCR - Brown), CA (RT-PCR - Wintermantel), SON RT-PCR - Guerrero/Brown); analyze plant samples from suspect fields and potential weed reservoirs; monitor whitefly patterns (in southern AZ) in relation to disease distribution, and investigate transmission/detection parameters for CYSDV-begomovirus complexes (Gilbertson). An initial goal was to determine if CYSDV would persist from year to year (2007 and onward) and if so, to make initial in roads into integrated management practices that could be implemented to reduce the damage to melon crops by this new disease in the region (AZ: Palumbo, Nolte, Taylor, Brown; CA: Natwick, Wintermantel). In a short timeframe, the team together with producers and PCAs (AZ Melon Task Force & CA Melon Board) determined that the best management and/or cultural practices involved a voluntary melon/watermelon host-free period (mid-July to mid-Aug), seasonal monitoring of whitefly and virus prevalence (Nolte, Taylor, Natwick) in order to better time pesticide applications (and avoid unnecessary applications), encourage managers to respond to virus survey/whitefly sticky trap information by applying pesticides when whiteflies dispersed to melon fields, implement 'best' practices pesticide regimes including new and soft chemistries when possible (including, row covers though economics precludes this practices, mostly) (Natwick and Palumbo), and continue with the development of CYSDV-resistant germplasm, which is presently lacking in the U.S. or elsewhere. Two promising CYSDV melon lines were examined with respect to inheritance of tolerance [TGR-1551 (PI 482420) and PI 313970] and >100 melon accessions were assessed for resistance in AZ and CA plots (McCreight). Numerous research updates were presented by various team members at extension sponsored educational meetings (hosts:Nolte, Taylor, Natwick), and a CYSDV bulletin was produced and distributed in AZ (Nolte, Brown, Taylor) and/or information posted at the UC-Davis IPM website. Task force and Melon Board meetings were held several times a year in AZ, CA, and SON to provide producers and field managers with the most up to date information. Team members presented several abstracts at their respective professional meetings, and refereed journal articles were published on the topic. PROJECT MODIFICATIONS: Not relevant to this project.

Impacts
a. Innovations in IPM for Melon Producers In AZ, the first Melon Task Force comprising producers, field managers, UA-Extension, and UA-Researcherswas established to come together to solve a common problem and save the melon industry. The Brown and C. Guerrero labs (UA and Universidad de Sonora) collaborated to establish a PCR lab for CYSDV detection at UNISON in Hermosillo. A technician trained in the Tucson lab and is proficient in the RT-PCR assay. Producers and government funds were combined to purchase PCR equipment and reagents for CYSDV detection in Sonora. b. Economic Benefits As a result of new knowledge that all cucurbits are hosts of CYSDV the AZ melon producers established a voluntary cucurbit host free period from mid-July to mid-August in Yuma County to save the fall melon crop there. Late-held watermelon fields are an important source of whiteflies and virus for the earliest planted melon fields. Certain melon varieties were identified as being more tolerant than others to CYDSV losses, making some of these the most commonly planted and thereby reducing lost profits. Knowledge that CYSDV infects plants in families other than the Cucurbitaceae has strengthened the interest in continuing research to identify important overseasoning virus and whitefly reservoirs throughout the region. c. Implementation of IPM A regional education and management program was initated for AZ and CA producers to encourage implementation of 'best' practices for whitefly control (research by J. Palumbo and E. Natwick). Producers and field managers are more aware of how their practices affect others. Knowledge-based research has given field managers facts upon which to base management strategies. Insecticide applications are encouraged based on timing of whitefly dispersal. Progress has been made in the breeding program toward identifying several CYSDV tolerant accessions. 2. Potential Impacts a. Implementation of IPM Continue to through the AZ Task Force and CA Melon Board to provide regional grower/manager education programs to familiarize growers with the virus and its epidemiology and establish practices that will minimize disease impact. Efforts are continuing in AZ and CA counties to be viligent about whitefly population increases, particularly early in the growing seasons, and to remove crop residues expediently after harvest. The USDA Salinas melon breeding program is continuing efforts to develop resistance varieties. Continued judicious use of best practices for whitefly management b. Safeguarding the environment& Economic benefits Continuing studies with the cooperation of producers and PCAs in Maricopa-La Paz counties to determine the natural host range of CYSDV in Arizona and California and to determine through transmission and molecular studies which hosts are most important as reservoirs of the virus in winter, spring, summer, and fall months. Knowledge will help reduce pesticide use. Knowledge of the spread of CYSDV into Maricopa and La Paz counties has encouraged producers there to join the effort in monitoring whitefly dispersal and alternate virus reservoirs, thereby expanding the region wide effort.

Publications

• 1. Referred Publications Papayiannis, L.C., S. Hunter, S.C., Lacofides, T., and Brown, J.K. 2009. Detection of Cucurbit yellow stunting disorder virus in cucurbit leaves using sap extracts and real-time TaqMan reverse transcription (RT) polymerase chain reaction (PCR). J. Phytopathol doi: 10.1111/j.1439-0434.2009.01647.x.
• Wintermantel, W.M., Brown, J.K., and Gilbertson, R.L. 2007. Widespread emergence of Cucurbit yellow Wintermantel, W.M., Hladky, L.L., Cortez, A.A., and Natwick, E.T. 2009. A new expanded host range of Cucurbit yellow stunting disorder virus includes three agricultural crops. Plant Disease 93: 685-690.
• 2. Short Communications Brown, J.K., Guerrero, J.C., Matheron, M., Olsen, M., and Idris, A.M. 2007. Widespread outbreak of Cucurbit yellow stunting disorder virus (CYSDV) in melon, squash, and watermelon crops in the Sonoran Plateau region of the Western USA and Pacific Coast of Mexico. Plant Dis. 91: 773.
• Kuo, Y.W., Rojas, M.R., Gilbertson, R. L., and Wintermantel, W.M. 2007. First report of Cucurbit yellow stunting disorder virus in California and Arizona, in association with Cucurbit leaf crumple and Squash leaf curl virus. Plant Dis. 91: 330.
• 3. Abstracts Nolte, K., Palumbo, J., Brown, J.K., Tellez, M., and Bealmer, S. 2008. Integrating GIS in the epidemiology and management of the Cucurbit yellow stunt disorder virus (CYSDV). The Horticulture Society of America, National Meeting, 2008 (Abstract; Oral Presentation).
• Wintermantel, W.M., Brown, J.K., and Gilbertson, R.L. 2007. Widespread emergence of Cucurbit yellow stunting disorder virus (CYSDV) in the southwestern desert melon production region of the United States and Mexico. APS meeting San Diego, CA July 28-August 1, 2007 (Oral Presentation).
• Papayiannis, L.C., Hunter, S.C., and Brown, J.K. 2008. Detection of Cucurbit yellow stunting disorder virus (CYSDV) in cucurbit leaves using sap extracts and real-time, quantitative polymerase chain reaction (qPCR). Third European Whitefly Symposium. Aguadulce, Almeria, Spain October 20-24, 2008.
• Papayiannis, L.C., S. Hunter, and J.K. Brown. 2008. Real time polymerase chain reaction (qPCR) for detection of Cucurbit yellow stunting disorder virus (CYSDV) in cucurbit leaves in total RNA and crude sap extracts. American Phytopathological Society meeting, St. Paul, MN. July 26-July 30, 2008 (Poster).