DEVELOPMENT AND DELIVERY OF INTEGRATED MANAGEMENT PACKAGES FOR THE MOST SERIOUS PEST AND DISEASES THREATENING US ALLIUM INDUSTRIES

• Sponsoring Institution: National Institute of Food and Agriculture
• Project Status: COMPLETE
• Funding Source: OTHER GRANTS
• Reporting Frequency: Annual
• Accession No.: 1016494
• Grant No.: 2018-51181-28435
• Cumulative Award Amt.: $3,291,766.00
• Proposal No.: 2018-03407
• Project Start Date: Sep 1, 2018
• Project End Date: Aug 31, 2024
• Grant Year: 2018
• Program Code: [SCRI]- Specialty Crop Research Initiative

Recipient Organization
WASHINGTON STATE UNIVERSITY
240 FRENCH ADMINISTRATION BLDG
PULLMAN,WA 99164-0001

Performing Department
Plant Pathology

Non Technical Summary
Onion and garlic are among the most valuable vegetable crops in the US and world. The annual farm-gate value of onion and garlic in the US exceeds $1.5 billion, with over $6 billion in added-value after processing. Over 20% of the world's onion seed is produced in the US and is valued at over $100 million annually. The ability of the US onion and garlic producers to meet domestic demand and compete on the world market is threatened by pests and diseases that are exceedingly complex and difficult to manage. Stakeholder surveys identified thrips, thrips-transmitted Iris yellow spot virus (IYSV), and soil-borne white rot as the main threats to the competitiveness and sustainability of the US Allium industry. Objectives of our proposal are to: 1) evaluate and implement practical, economical, environmentally sound and socially acceptable IPM tactics for control of thrips, IYSV and white rot; 2) release to stakeholders onion germplasm resistant to thrips and IYSV; and 3) communicate results and approaches to stakeholders through spoken, written, and electronic (websites and an eXtension portal Learning Network) venues. These objectives align directly with foci of the USDA Specialty Crop Research Initiative to: (1) identify and conduct research in plant breeding, genetics, and genomics to improve crop characteristics; (2) address threats from pests and diseases; and (3) improve production efficiency, productivity, and profitability.

Animal Health Component

80%

Research Effort Categories

Basic

20%

Applied

80%

Developmental

0%

Classification

Knowledge Area (KA)	Subject of Investigation (SOI)	Field of Science (FOS)	Percent
216	1451	1130	20%
211	0110	1081	20%
212	3110	1160	20%
601	4030	3010	20%
201	4020	3080	20%

Knowledge Area
212 - Pathogens and Nematodes Affecting Plants; 601 - Economics of Agricultural Production and Farm Management; 211 - Insects, Mites, and Other Arthropods Affecting Plants; 216 - Integrated Pest Management Systems; 201 - Plant Genome, Genetics, and Genetic Mechanisms;

Subject Of Investigation
0110 - Soil; 1451 - Onion, garlic, leek, shallot; 3110 - Insects; 4020 - Fungi; 4030 - Viruses;

Field Of Science
1130 - Entomology and acarology; 1160 - Pathology; 1081 - Breeding; 3010 - Economics; 3080 - Sociology;

Keywords

ipm

iris yellow spot virus

onion

host resistance

soil borne pathogens

sustainability

thrips

Goals / Objectives
The objectives of this project are to:Evaluate and implement sustainable IPM control tactics for onion thripsEvaluate and implement approaches for sustainable control of IYSVEvaluate and implement sustainable IPM control tactics for white rot Estimate profitability and assess social acceptance of new pest management approache

Project Methods
Objective I. Evaluate and implement sustainable IPM tactics for thripsIA. Evaluate multiple tactics for onion thrips management in field plotsThree onion phenotypes will be evaluated including two thrips-resistant, semi-glossy selections with significant amounts of total epicuticular wax, and a commercial cultivar with waxy foliage (=control). Past research has clearly shown that semi-glossy onions suffer significantly less thrips damage compared with waxy types, and can have more total epicuticular waxes than susceptible waxy onions. The standard commercial cultivars will be waxy and commonly grown in NY (cv. Bradley) and OR (cv. Vaquero). Three rates of N application will be examined including the standard industry rate and two that are comparatively lower. Past research has shown that lower N reduces thrips densities. Two insecticide programs will be evaluated including i) a standard weekly spray program and ii) an action threshold-based program and an untreated control for a total of three treatments.IB. Implement novel thrips management program in commercial fieldsThe novel thrips management program will include the IPM tactics evaluated in Obj. IA that performed the best in each region. For example, the reduced rate of nitrogen that reduces thrips damage, but does not reduce yield, and the novel insecticide program that uses an action threshold. The standard management program will include the recommended rate of nitrogen and a standard weekly insecticide program. These two management programs will be evaluated using two cultivars, the best performing thrips-resistant semi-glossy selection from Obj. IA and a commercial standard. In each field quarter (plot), thrips larval densities will be monitored weekly from 10 plants at 5 randomly-selected locations. This information will be used to determine if an insecticide application is needed for the novel program.IC. Development of elite thrips-resistant populations of long and short day onionsSemi-glossy selections that support fewer thrips and suffer significantly less feeding damage have been crossed with elite onion long-day (WI) and short-day (NM) populations with waxy foliage. Hybrids will be backcrossed (BC) on an annual cycle to the elite populations. BC progenies will also be genotyped for a SNP in the male-fertility restoration locus on chromosome 2 and those possessing the recessive ms allele selected. Selected BC progenies will be intercrossed and gas chromatography mass spectrometry (GCMS) used to identify progenies with lower amounts of H16 and higher amounts of fatty alcohols and alkanes. Individuals that are semi-glossy, have relatively high amounts of fatty alcohols and alkanes, and homozygous recessive at Ms will be caged, intercrossed with bees, and seed separately harvested from each plant to produce half-sib (HS) families.?OBJECTIVE II. evaluate and RELEASE ONION GERMPLASM to mitigate the effects of IYSVThe five best field-selected onion breeding lines that have performed well under heavy IYSV pressure will be evaluated in fields in NM and WA and compared with a susceptible commercial cultivar. The selected lines originated from crosses between early Sweet Spanish and Grano germplasm and have semi-glossy foliage, which is less vulnerable to thrips damage. These selections and the standard control will be evaluated under well-watered (not to exceed 30% managed allowed depletion [MAD] based upon crop evapotranspiration [ET]) and water-limited conditions (50% MAD based upon crop ET for the last three months of crop growth). Ten plants will be randomly selected (and labeled using plastic tags) in each field plot and IYS incidence and severity will be recorded. The relative levels of IYSV will be estimated by ELISA and PCR. Plant height, leaf number, and sheath diameter will be measured to determine any association between IYS incidence and severity and plant size. Leaf colors will be quantified using a chromameter. We will measure leaf area index (LAI) of plants in the field using a photosynthetically active radiation (PAR)/LAI ceptometer.OBJECTIVE III. EVALUATE AND IMPLEMENT SUSTAINABLE IPM TACTICS FOR WHITE ROTIIIA. Identify effective dosages of novel germination biostimulants Gas chromatography (GC) mass spectrometry (MS) and GC-pulsed flame photometric detection(PFPD) will be used to identify and characterize volatile sulfur compounds from various sources, including onion, garlic, and natural byproducts from the Allium industry (e.g. garlic powder, garlic juice, garlic processing effluent, and onion waste compost). Compounds will be identified by mass spectroscopy, and concentrations determined using solid phase microextraction GC-MS and GC-PFPD. The sulfur precursors in Allium byproducts will also be analyzed after enzymatic conversion. Dose response experiments will be conducted using replicated petri-plate assays. The viability of intact sclerotia will be tested by plating surface-sterilized sclerotia on WA. Data will be averaged across three experiments. Each treatment will have 5 replicates (500 sclerotia/treatment) and the experiment will be performed twice. The efficacy of sulfur compounds on sclerotia germination in various combinations will be determined in petri plate assays as described above.?IIIB. Evaluate germination biostimulants with in-furrow fungicide applications to reduce onion white rot losses under field conditionsGermination biostimulants and fungicide applications will be assessed for the control of white rot in the greenhouse and in field plots under different soil types and growing conditions. DADS will be included as a control for comparison with the germination biostimulants. Fungicides currently labeled for white rot control in onion (e.g. tebuconazole, fludioxonil), as well as novel fungicide chemistries with the potential to suppress white rot, will be included in the study at labeled or suggested rates. Experiments will include main plots consisting of germination biostimulants and subplots of in-furrow fungicide treatments. Disease and yield will be determined from the center two rows taken from the middle of each plot. Germination biostimulants will be spread and incorporated, chemigated, or shank-injected depending on the formulation (i.e. liquid, powder). Germination biostimulants will be applied in the spring of 2019 at rates determined to be most stimulatory (Obj. IIIA). The number of sclerotia will be quantified in soil samples before and after stimulant treatments and periodically throughout the trial.OBJECTIVE IV. IMPROVE PROFITABILITY BY TRANSLATING RESEARCH FINDINGS INTO PRACTICAL PEST MANAGEMENT PROGRAMS AND ASSESS THE SOCIAL BENEFITS OF IMPROVED MANAGEMENT TECHNIQUESWe will collaborate with stakeholders to obtain pesticide data for control of thrips in major US Allium growing regions. Product use, application rates, application method, and dates of application will be combined with pesticide cost data collected from university sources and agricultural chemical dealers. Yields and grade distributions corresponding with current and novel practices for thrips and IYSV will also be collected. Enterprise budgeting will be used to establish baseline cost, return, and breakeven estimates. Partial budgeting will be used to conduct cost benefit analyses that compare grower level impacts of different combinations of alternative management strategies developed in Obj. I and II. Grower level impacts will be aggregated to estimate regional impacts of improved management techniques. Regional analyses will be used to estimate the potential industry-wide impacts of increased yields and reduced pesticide use resulting from novel thrips and IYSV management strategies. To evaluate the economic benefits of improved white rot control methods, we will collaborate with stakeholders to estimate the portion of acreage currently impacted by the pest and diseases.

Progress 09/01/18 to 08/31/24

Outputs
Target Audience:Fellow plant pathologists, entomologists, breeders, ag. economiists, hortiulturalists, extension specialists, and stakeholders. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?Funds were used to partially support the summer salary of a PhD student who conducted the study. The PhD student completed her doctorate. Additionally, funding supported undergraduate research assistants who assisted in this research. Training of graduate and undergraduate students with regards to trait measurement, instrument use, disease screening, seed cleaning, proper seed storage, statistical analysis, and data collection. Hosted two high school students as interns for summer to work on research project. The project provided mentorship of twopostdoctoral research associates who coordinated the planning, preparation, execution, and reporting of work related to these efforts. An undergraduate student technician was also trained in mycology and plant pathology techniques through their involvement in research activities. How have the results been disseminated to communities of interest?Results have been shared only with Cornell Cooperative Extension Educators, private agricultural consultants and New York onion growers in the Elba Muck production region where the study was conducted. Future opportunities will allow us to share the information at other onion grower meetings throughout North America as well as extension newsletters. We also intend to publish the results for the scientific community. An NMSU Onion Field Day was held on Wednesday, June 26, 2019, Wednesday, June 29, 2022, Wednesday, June 6, 2023. In total, there were 164 attendees. At each field day, a presentation was made regarding our research related to breeding for resistance to onion thrips and Iris yellow spot. In 2022, a presentation was made to the grant advisory committee regarding progress towards resistance to onion thrips and Iris yellow spot. Results have been disseminated through six regional grower meetings, one University seminar, and six scientific conferences including the American Phytopathological Society meetings, National Allium Research Conferences, and others. Publications included a total of three refereed, peer-reviewed manuscripts, three abstracts at professional meetings, two peer-reviewed technical reports, four Central Oregon Agricultural Research and Extension Center annual reports, and two publications in Onion World. What do you plan to do during the next reporting period to accomplish the goals? Nothing Reported

Impacts
What was accomplished under these goals? To reduce levels of IYSV in New York onion fields, early-season applications of methomyl supplemented a season-long insecticide program aimed at managing the vector of IYSV, onion thrips adults. Over this multi-year study, we observed a 65-68% reduction in incidence of IYSV in fields late in the season that received the methomyl applications compared with those that only received the season-long insecticide program. Mean bulb weight of onions from fields supplemented with the methomyl sprays were 23% higher than those that did not, but the difference was not statistically significant. A third year of this study is currently underway and similar trends have been observed. When exposed to high onion thrips pressure conditions and Iris yellow spot virus both of which are conducive for Iris yellow spot (IYS) disease development, plants of NMSU breeding lines that had been selected for reduced IYS disease symptoms exhibited fewer thrips per leaf early in the growing season, a lower IYS disease severity early in the growing season, and a greater bulb weight at harvest than plants of an open-pollinated landrace that were grown under the same conditions. The same NMSU breeding lines were shown to possess a high photosynthetic rate than the above-mentioned landrace when both were grown under biotic stressful growing conditions. Growth chamber and field trials were conducted to evaluate encapsulated garlic oil and diallyl disulfide (DADS), which is easier to handle and apply than liquid formulations. Encapsulated garlic oil and DADS were applied to naturally infested soils either as a dry formulation or as a suspension in water. Both the dry and wet formulations of encapsulated garlic oil and DADS significantly reduced sclerotia counts similar to the DADS-treated control. Trap crops were evaluated as a source of sclerotial germination stimulants in greenhouse and field trials. Infested plots were either left fallow or planted to onions; plots with onions were terminated with glyphosate at the second through sixth true leaf stages. A 24% reduction in sclerotia was observed when onions were terminated at the second leaf stage; however, sclerotia counts were similar to fallow plots by the third leaf termination timing and were greater at later termination timings. Field trials were conducted over two seasons to evaluate Pyraziflumid applied in-furrow for white rot management. Pyraziflumid significantly increased stand counts and plant heights and significantly reduced disease severity compared to the control. At harvest, plots treated with higher rates of Pyraziflumid exhibited increased marketable yields compared to the non-treated control. Diallyl disulfide (DADS) and other volatile sulfur compounds can stimulate sclerotial germination, and a dose-response was observed. Also, garlic juice, powder, raw onion, and the cabbages could stimulate sclerotial germination. However, the laboratory soil incubation experiments demonstrated the strong interaction of organic sulfur compounds with soil, reducing volatile sulfur compounds' efficacy. In addition, these compounds are often highly volatile and difficult to handle and apply. Therefore, a study was conducted to encapsulate DADS and garlic oil with β-cyclodextrin (β-CD) to protect sulfur volatiles from interactions with soil and againstoxidation, degradation, and evaporation. Microcapsule extract analysis showed that garlic oil and DADS were successfully encapsulated with greater than 90% recovery of the starting product. In addition, the micro-encapsulation process did not change the chemical compounds, but their proportions were altered. Furthermore, lab and growth chamber incubation experiments revealed that DADS andDAScould be slowly released into the soil from microcapsules and worked effectively for white rot sclerotia germination. When compared to liquid DADS and garlic oil, the encapsulated formulations DADS and garlic oil are equally effective but easier to handle, which can provide more flexibility in terms of timing, placement, and method of sclerotia germination stimulant applications. We estimated the benefits from public investment in research to develop IPM-based onion thrips management techniques. When estimated using the assumption of a maximum IPM adoption rate of 58%, the net present value of the research is$15.91 million, the benefit-cost ratio is 4.00, and the internal rate of return is 32%. A comprehensive analysis for evaluation of optimal use of insecticides and in season nitrogen fertilization to maximize profitability of dry bulb onion production in the Treasure Valley was conducted utilizing all three years of data from the research project. An assessment was administered to garlic and onion growers and handlers in Washington and California to improve understanding of stakeholder perceptions of allium white rot disease and to identify best practices for increasing adoption of new approaches to managing the disease. The survey captured about 46% of planted onion hectares and about 76% of planted garlic hectares in the two states. Respondents identified collaboration with commercial growers and demonstration of new management practices on a commercial scale as the highest impact practices for increasing confidence in adoption of new management techniques for white rot. A model was developed to improve understanding of factors that impact disease-free yield of onion produced in fields that have been naturally infected with the white rot pathogen and to quantify the responsiveness of yield to reductions in sclerotia populations. Results indicated that every one percent decrease in sclerotia populations resulted in a 0.07 percent increase in disease free yield. Results also indicated a high level of responsiveness of yield to fungicides use highlighting the important role of fungicides in development of white rot management programs that are economically viable.

Publications

• Type: Journal Articles Status: Published Year Published: 2024 Citation: 1) Yanping L. Qian, Gia Khuong Hoang Hua, Jeness C. Scott, Jeremiah K.S. Dung, and Michael C. Qian*. Encapsulation of Garlic Oil and Commercial Diallyl Disulfide Oil with ?-Cyclodextrin for Garlic White Rot Control. Crop Protection, Vol. 178, April 2024, pp106597 https://doi.org/10.1016/j.cropro.2024.106597
• Type: Journal Articles Status: Published Year Published: 2022 Citation: 2) Yan Ping L. Qian, Gia Khuong Hoang Hua, Jeness C. Scott, Jeremiah K.S. Dung, and Michael C. Qian. Evaluation of Sulfur-based Biostimulants for the Germination of Sclerotium cepivorum Sclerotia and their Interaction with Soil. J. Agric. Food Chem. Nov.18, 2022, 70, 48, 15038-15045 https://doi.org/10.1021/acs.jafc.2c05862
• Type: Journal Articles Status: Published Year Published: 2022 Citation: Regan, K.H., and B.A. Nault. 2022. Impact of reducing synthetic chemical inputs on pest and disease management in commercial onion production systems. Agronomy 12(6), 1292; https://doi.org/10.3390/agronomy12061292
• Type: Journal Articles Status: Published Year Published: 2024 Citation: Komondy, L., C. Hoepting, M. Fuchs, S. J. Pethybridge, and B. A. Nault. 2024. Identifying onion fields at risk of Iris yellow spot virus in New York. Plant Dis. https://doi.org/10.1094/PDIS-10-23-2097-RE
• Type: Journal Articles Status: Published Year Published: 2023 Citation: Greenway, G., S. Reitz, and B. A. Nault. 2023. A cost-benefit analysis of novel IPM-based approaches to onion thrips management in US dry bulb onions. Horticulturae 9(11), 1219; https://doi.org/10.3390/horticulturae9111219).
• Type: Journal Articles Status: Published Year Published: 2023 Citation: Komondy, L., C. Hoepting, M. Fuchs, S. J. Pethybridge, and B. A. Nault. 2023. Spatiotemporal patterns of iris yellow spot virus and its onion thrips vector, Thrips tabaci, in transplanted and seeded onion fields in New York. Plant Dis. 108(2): 398-406; https://doi.org/10.1094/PDIS-05-23-0930-RE
• Type: Journal Articles Status: Published Year Published: 2023 Citation: Sharma, S. and C.S. Cramer. 2023. Reduced Iris yellow spot symptom expression in the selected germplasm. Vegetable Research 3: 26. https://doi.org/10.48130/VR-2023-0026.
• Type: Journal Articles Status: Published Year Published: 2022 Citation: Shahabeddin Nourbakhsh, S. and C.S. Cramer. 2022. Onion germplasm possess lower early season thrips numbers. Horticulturae 8:123. https://doi.og/10.3390/horticulturae8080123
• Type: Journal Articles Status: Published Year Published: 2022 Citation: Shahabeddin Nourbakhsh, S. and C.S. Cramer. 2022. Onion size measurements as predictors for onion bulb size. Horticulturae 8:682. https://doi.og/10.3390/horticulturae8080682.
• Type: Journal Articles Status: Published Year Published: 2021 Citation: Cramer, C.S., S. Mandal, S. Sharma, S. Shahabeddin Nourbakhsh, I. Goldman, and I. Guzman. 2021. Recent advances in onion genetic improvement. Agronomy 11:482. https://doi.og/10.3390/agronomy110300482.
• Type: Conference Papers and Presentations Status: Published Year Published: 2021 Citation: Greenway, G., N. Kamal, S. Shahabeddin Nourbakhsh, and C.S. Cramer. 2021. Estimating potential changes in costs and returns from use of a partially onion thrips-resistant cultivar and action-based spray thresholds in Idaho and Eastern Oregon. Southwestern Entomologist. 46:349-356. https://doi.og/10.3958/059.046.0206.
• Type: Conference Papers and Presentations Status: Published Year Published: 2020 Citation: Hua, K. and Dung, J.K.S. 2020. Use of Alliums as trap crops to reduce white rot inoculum in infested field soil. Abstract. Phytopathology 110:S2.170.
• Type: Other Status: Published Year Published: 2022 Citation: Dung, J.K.S. and Hua, K. 2022. Comparison of fungicides for control of white rot on garlic in Oregon, 2020-2021. Plant Disease Management Reports 16:CF029. doi: 10.1094/PDMR16
• Type: Journal Articles Status: Published Year Published: 2021 Citation: Kamal, N. S. Shahabeddin Nourbakhsh, and C.S. Cramer. 2021. Reduced Iris yellow spot symptoms through selection within onion breeding lines. Horticulturae 7:12. https://doi.og/10.3390/horticulturae7060012.
• Type: Journal Articles Status: Published Year Published: 2019 Citation: Singh, N. and C.S. Cramer. 2019. Improved tolerance for onion thrips and Iris yellow spot in onion plant introductions after two selection cycles. Horticulturae 5:18. doi 10.3390/horticulturae5010018
• Type: Theses/Dissertations Status: Published Year Published: 2021 Citation: Shahabeddin Nourbakhsh, S. 2021. Thrips tolerance in onions: An examination of thrips population response to different plant size and foliage characteristics, and their effects on bulb weight. MS Thesis, New Mexico State Univ.
• Type: Other Status: Published Year Published: 2021 Citation: Cramer, C.S. and I. Guzman. 2021. Breeding for resistance to Iris yellow spot. Onion World. July/August, pp. 10-13.
• Type: Journal Articles Status: Published Year Published: 2024 Citation: Hua, G.K.H., Wilson, R.G., and Dung, J.K.S. 2024. Evaluation of bait crops for the integrated management of white rot (Sclerotium cepivorum) in Allium crops. Plant Disease 108(1):118-124. https://doi.org/10.1094/PDIS-04-23-0688-RE.
• Type: Conference Papers and Presentations Status: Published Year Published: 2022 Citation: Hua, K., Qian, Y.P., Qian, M., Wilson, R., and Dung, J.K.S. 2022. Use of sulfur compounds and Allium lure crops to reduce white rot inoculum in infested soils. Phytopathology 112(115):S3.42-43
• Type: Conference Papers and Presentations Status: Published Year Published: 2022 Citation: Hua, K., Wilson, R., and Dung, J.K.S. 2022. Use of Alliums as trap crops to reduce white rot inoculum in infested field soil. 2022 National Allium Research Conference.
• Type: Other Status: Published Year Published: 2021 Citation: Dung, J.K.S. and Hua, K. 2021. Comparison of fungicides for control of white rot on garlic in Oregon, 2019-2020. Plant Disease Management Reports 15:V032. doi: 10.1094/PDMR15
• Type: Other Status: Published Year Published: 2022 Citation: Hua, K., Wilson, R., and Dung, J.K.S.. 2022. Setting a Trap: Can Early Terminated Allium Trap Crops Reduce White Rot Infestations? Onion World (January 2022):16-18.
• Type: Other Status: Published Year Published: 2020 Citation: Hua, G.H.H. and Dung, J.. 2020. Here Today, Gone Tomorrow: Can Early Terminated Onion Trap Crops Reduce White Rot Infestations? Onion World (November 2020):32-33.
• Type: Other Status: Published Year Published: 2023 Citation: Dung, J., Scott, J., Qian, Y.P., and Qian, M. 2023. Evaluating Encapsulated Sclerotial Germination Stimulants for White Rot Management. Central Oregon Agricultural Research and Extension Center 2023 Annual Report:23-25.
• Type: Other Status: Published Year Published: 2021 Citation: Hua, K., and Dung, J. 2021. Microplot evaluation of Allium lure crops to reduce populations of white rot sclerotia in infested soil. Central Oregon Agricultural Research and Extension Center 2021 Annual Report:31-33.
• Type: Other Status: Published Year Published: 2020 Citation: Hua, K., and Dung, J.K.S. 2020. Use of Alliums as trap crops to reduce white rot inoculum in infested soils. Central Oregon Agricultural Research and Extension Center 2020 Annual Report:21-24.
• Type: Other Status: Published Year Published: 2020 Citation: Hua, K., and Dung, J.K.S. 2020. Comparison of fungicides for control of white rot on garlic in Oregon, 2019-2020. Central Oregon Agricultural Research and Extension Center 2020 Annual Report:19-20.

Progress 09/01/22 to 08/31/23

Outputs
Target Audience:Onion stakeholders, research and extension specialists/scientists at university, government and industry laboratories. Changes/Problems:None What opportunities for training and professional development has the project provided?Objectives 1 and 2: Funds were used to partially support the summer salary of a PhD student, Lidia Komondy, who conducted the study. Additionally, funding supported undergraduate research assistants who assisted in this research. Objective 3 involved the mentorship of a postdoctoral research associate who coordinated the planning, preparation, execution, and reporting of work related to these efforts. Training of graduate and undergraduate students with regards to trait measurement, instrument use, disease screening, seed cleaning, proper seed storage, statistical analysis, and data collection. How have the results been disseminated to communities of interest?An NMSU Onion Field Day was held on Wednesday, June 6, 2023. There were 37 attendees. A presentation was made regarding our research related to breeding for resistance to onion thrips and Iris yellow spot. Two publications were produced. Results have been shared with the New York onion growers whose fields were offered for this research. Future opportunities will allow us to share the information at other onion grower meetings in the Great Lakes region as well as extension newsletters. We also anticipate publishing the results for the scientific community. Results have been shared with the New York onion growers whose fields were offered for this research. Future opportunities will allow us to share the information at other onion grower meetings in the Great Lakes region as well as extension newsletters. We also anticipate publishing the results for the scientific community. Hua, G.K.H., Wilson, R.G., and Dung, J.K.S.. 2023. Evaluation of lure crops for the integrated management of white rot (Sclerotium cepivorum) in Allium crops. Plant Disease (in print). https://doi.org/10.1094/PDIS-04-23-0688-RE. Qian, Y., Hua, G.K.H., Scott, J.C., Dung, J.K.S., and Qian, M. 2022. Evaluation of sulfur-based biostimulants for the germination of Sclerotium cepivorum sclerotia and their interaction with soil. Journal of Agricultural and Food Chemistry Manuscript 70(48):15038-15045. https://doi.org/10.1021/acs.jafc.2c05862 Iftikhar, R., A. Ghosh, and H.R. Pappu (2023). Mitochondrial genetic diversity of Thrips tabaci (Thysanoptera: Thripidae) in onion growing regions of the USA.Journal of Economic Entomology. Published On-line April 13, 2023 https://doi.org/10.1093/jee/toad039 Greenway, G. 2023. Cost of Production and IPM Analysis for Treasure Valley Onions. Idaho Malheur County Onion Growers Annual Meeting, February 7, Ontario OR. What do you plan to do during the next reporting period to accomplish the goals?We intend to harvest onions in the fields that received and did not receive the additional insecticide applications in the event that the additional applications reduced thrips populations and their damage. We also would like to repeat this study in 2024.We will disseminate the assessment instrument for evaluation of stakeholder perceptions of white rot, evaluate the economic benefits of improved approaches to white rot, and submit a drafted manuscripts evaluating the costs and benefits of reduced nitrogen fertilization in onions. Will continue the barcoding of additional onion thrips populations from different onion growing regions of the country.

Impacts
What was accomplished under these goals? We attempted to reduce IYSV incidence in onion fields by applying additional foliar applications of insecticides during the initial onion thrips colonization period. Four pairs of onion fields were selected such that one field in each pair was treated with at least two applications of methomyl in addition to insecticides applied in a season-long thrips management program; the other field received only the insecticides applied in the season-long program. Unfortunately, the final mean percentage of onions testing positive for IYSV in fields that received the additional insecticide sprays was 68%, whereas those that received the standard insecticide spray program was 42% When exposed to high onion thrips pressure conditions and Iris yellow spot virus both of which are conducive for Iris yellow spot (IYS) disease development, plants of NMSU breeding lines that had been selected for reduced IYS disease symptoms exhibited fewer thrips per leaf early in the growing season, a lower IYS disease severity early in the growing season, and a greater bulb weight at harvest than plants of an open-pollinated landrace that were grown under the same conditions. A cohort of 39 onion growers were surveyed to evaluate perceived risk from the most serious pests and diseases facing the allium industry, to evaluate willingness to adopt new approaches to management, and to identify practices that would improve adoption of IPM. A manuscript was submitted March 21, 2023 and is pending publication. A second survey was developed for dissemination to a cohort of onion and garlic growers in California and Washington to assess the status of white rot, to evaluate current risk perceptions, and to estimate economics benefits of improved approaches to management. In the current study, 84 T. tabaci specimens were collected from Allium cepa from 15 different locations comprising four states of the USA. A total of 93 COI gene sequences including 9 accessions from GenBank originated from Raleigh, USA were analyzed to understand the genetic diversity and structure of T. tabaci. Twelve distinct haplotypes of T. tabaci infesting A. cepa were identified. Based on the phylogenetic analysis, all of the populations collected during the study clustered with thelytokous lineage. While nine T. tabaci sequences retrieved from GenBank comprised 4 haplotypes and corresponded to leek-associated arrhenotokous lineage.

Publications

• Type: Journal Articles Status: Published Year Published: 2022 Citation: Regan, K.H., and B.A. Nault. 2022. Impact of reducing synthetic chemical inputs on pest and disease management in commercial onion production systems. Agronomy 12(6), 1292; https://doi.org/10.3390/agronomy12061292.
• Type: Journal Articles Status: Under Review Year Published: 2023 Citation: Greenway, G., S. Reitz, S. Rondon and B.A. Nault. Extension Impacts on Onion IPM: Current Perspectives from the Industry. Journal of Extension.
• Type: Journal Articles Status: Published Year Published: 2023 Citation: Sharma, S. and C.S. Cramer. 2023. Reduced Iris yellow spot symptom expression in the selected germplasm. Vegetable Research 3: 26. https://doi.org/10.48130/VR-2023-0026.
• Type: Journal Articles Status: Published Year Published: 2023 Citation: Wood, J.B., C.S. Cramer, R. Steiner, R. Heerema, B.J. Schutte, and I. Guzman. 2023. Onions selected for reduced symptom expression of Iris yellow spot have higher photosynthetic rates. HortScience 58:254-258. https://doi.rog/10.21273/HORTSCI16878-22.
• Type: Journal Articles Status: Published Year Published: 2022 Citation: Qian, Y., Hua, G.K.H., Scott, J.C., Dung, J.K.S., and Qian, M. 2022. Evaluation of sulfur-based biostimulants for the germination of Sclerotium cepivorum sclerotia and their interaction with soil. Journal of Agricultural and Food Chemistry Manuscript 70(48):15038-15045. https://doi.org/10.1021/acs.jafc.2c05862 .
• Type: Journal Articles Status: Published Year Published: 2023 Citation: Hua, G.K.H., Wilson, R.G., and Dung, J.K.S.. 2023. Evaluation of lure crops for the integrated management of white rot (Sclerotium cepivorum) in Allium crops. Plant Disease (in print). https://doi.org/10.1094/PDIS-04-23-0688-RE.
• Type: Journal Articles Status: Under Review Year Published: 2023 Citation: Qian, Y., Hua, G.K.H., Dung, J.K.S., and Qian, M. 2023. Encapsulation of garlic oil and diallyl disulfide with ?-cyclodextrin for white rot control in Allium crops. Crop Protection (submitted).
• Type: Conference Papers and Presentations Status: Published Year Published: 2022 Citation: Hua, K., Qian, Y.P., Qian, M., Wilson, R., and Dung, J.K.S.. 2022. Use of sulfur compounds and Allium lure crops to reduce white rot inoculum in infested soils. Abstract. Phytopathology 112(115):S3.42-43
• Type: Journal Articles Status: Published Year Published: 2022 Citation: 2. Iftikhar, R., A. Ghosh, and H.R. Pappu (2023). Mitochondrial genetic diversity of Thrips tabaci (Thysanoptera: Thripidae) in onion growing regions of the USA Journal of Economic Entomology. Published On-line April 13, 2023 https://doi.org/10.1093/jee/toad039

Progress 09/01/21 to 08/31/22

Outputs
Target Audience:Onion stakeholders, research and extension specialists/scientistsat university, government and industry laboratories Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?Cramer, NMSU:Training of graduate and undergraduate students with regards to trait measurement, instrument use, disease screening, seed cleaning, proper seed storage, statistical analysis, and data collection. Hosted two high school students as interns for summer to work on research project. Reitz, OSU:One post-doc worked on the project; eleven undergraduate research assistants, including two who conducted their undergraduate research thesis as part of the project. Pappu, WSU: One post-doctoral fellow worked full time on the project; received training in determining IYSV levels in onion genotypes using qPCR, carried out barcoding of onion thrips collected from various onion producing areas in different states How have the results been disseminated to communities of interest?Oral and poster presentations on white rot management, screening for IYSV resistance and thrips resistance, optimal insecticidal regimen for thrips control were made by the members of the team: Nault, Cramer, Reitz, Havey, Pappu, and Dung.was made to the stakeholder community at the 2022 National Allium Research Conference in Denver in February 2022. An NMSU Onion Field Day was held on Wednesday, June 29, 2022. There were 73 attendees. A presentation was made regarding our research related to breeding for resistance to onion thrips and Iris yellow spot. A presentation was made to the grant advisory committee regarding progress towards resistance to onion thrips and Iris yellow spot. Four publications were produced and five additional presentations were made. Research reports available at https://agsci.oregonstate.edu/mes/malheur-experiment-station Meeting presentations Idaho-Malheur County Onion Growers Annual Meeting, (Reitz: 2020, 2021, 2022) Pacific Northwest Vegetable Association (Reitz: 2019, 2020, 2021, 2022; Greenway 2022). Popular Press:Greenway, G. and Feibert, E. 2022. Crunching the Numbers: An Economic Analysis of IPM-Based Thrips Management Strategies. Onion World. March 9, 2022. https://onionworld.net/2022/03/09/crunching-the-numbers-an-economic-analysis-of-ipm-based-thrips-management-strategies/ An Oral presentation of the economics of IPM strategies was delivered at the annual Pacific Northwest Vegetable Association meeting November 16th-17th 2022. What do you plan to do during the next reporting period to accomplish the goals?An assessment of grower adoption of IPM approaches to management will be administered and evaluated to estimate the societal benefits of the research.We intend to repeat the field research project on optimizing the pesticide regimen for thirps control.Complete peer-review manuscripts for publication

Impacts
What was accomplished under these goals? White rot treatments were identified that produced the greatest benefits relative to the cost of the treatment. Incorporating in furrow fungicide treatments at planting was estimated to increase yield by an average of 1.78 tons per acre resulting in an estimated revenue increase of $320-$400 per acre. Three years of data from the Malheur Experiment Station was used to evaluate the costs and returns associated with various IPM strategies and evaluate the benefit cost ratios associated with various managerial tactics. Investment in judicious nitrogen management was estimated to return between $2-$4 for each dollar spent. Judicious insecticide use was also found to provide a strong return on investment. Natural variation in onion for amounts and types of epicuticular waxes was assessed and specific accessions were identified with large amounts of total wax and lighter green leaf color associated with resistance to onion thrips. Independent sources of this unique phenotype were intercrossed to produce a new populationwith unique wax profiles and suffer less feeding damage by thrips. Seed is being increased of the population for more evaluations and eventual release to stakeholders. When exposed to high onion thrips pressure conditions and Iris yellow spot virus both of which are conducive for Iris yellow spot (IYS) disease development, NMSU breeding lines that had been selected for reduced disease symptoms exhibited fewer thrips per plant early in the growing season, a lower disease severity and fewer plants with disease early in the growing season, and a greater bulb size at harvest than a commercial cultivar grown under the same conditions. Field trials have demonstrated that threshold-based sampling can successfully reduce insecticide applications without sacrificing yield and quality. We demonstrated that the threshold-based insecticide program can outperform the calendar-based insecticide program in terms of the benefit/cost ratio. Onion thrips (Thrips tabaci Lindeman, Thysanoptera: Thripidae) is a key pest of Allium cepa in the USA. Additionally, T. tabaci vectors IYSV. However, there is limited information available on the genetic variation within and between T. tabaci populations in the USA and its key evolutionary parameters. In the current study, 83 T. tabaci specimens were collected from A. cepa from 15 different locations comprising four states of the USA. A total of 92 COI gene sequences of T. tabaci from A. cepa were analyzed to understand the genetic diversity and structure of T. tabaci collected from onion host. Seven distinct haplotypes of T. tabaci infesting A. cepa were identified from the current collection, while nine T. tabaci sequences retrieved from GenBank comprised 5 haplotypes. Overall, 15 haplotypes of T. tabaci infesting A. cepa were identified in the world that includes the ten haplotypes in the USA. In the phylogenetic analysis, all the populations collected during the study clustered with thelytokous lineage, while T. tabaci sequences retrieved from GenBank corresponded to leek-associated arrhenotokous lineage. The highest genetic variation was found in Elba and Malheur populations with 3 haplotypes identified in each. The results suggest that haplotypes 1 and 7 are more frequently prevailing haplotypes in the north-western USA, with haplotype 1 being the predominant all over the country. The eastern USA appears to have a more diverse group of haplotypes. The populations from Hungary constituted distinct haplotypes and a haplotype from Kingston linked it with the predominant haplotype.

Publications

• Type: Journal Articles Status: Published Year Published: 2022 Citation: Regan, K.H. and B.A. Nault. 2022. Impact of reducing synthetic chemical inputs on pest and disease management in commercial onion production systems. Agronomy 12(6), 1292; https://doi.org/10.3390/agronomy12061292
• Type: Journal Articles Status: Published Year Published: 2022 Citation: Havey, M.J. 2022. Variation for epicuticular waxes among plant introductions of onion. Hortscience 57(9):10591063. https://doi.org/10.21273/HORTSCI16697-22https://doi.org/10.21273/HORTSCI16697-22
• Type: Journal Articles Status: Published Year Published: 2022 Citation: Shahabeddin Nourbakhsh, S. and C.S. Cramer. 2022. Onion germplasm possess lower early season thrips numbers. Horticulturae 8:123. https://doi.og/10.3390/horticulturae8080123
• Type: Journal Articles Status: Published Year Published: 2022 Citation: Shahabeddin Nourbakhsh, S. and C.S. Cramer. 2022. Onion size measurements as predictors for onion bulb size. Horticulturae 8:682. https://doi.og/10.3390/horticulturae8080682.
• Type: Journal Articles Status: Published Year Published: 2021 Citation: Cramer, C.S., S. Mandal, S. Sharma, S. Shahabeddin Nourbakhsh, I. Goldman, and I. Guzman. 2021. Recent advances in onion genetic improvement. Agronomy 11:482. https://doi.og/10.3390/agronomy110300482.
• Type: Theses/Dissertations Status: Published Year Published: 2021 Citation: Shahabeddin Nourbakhsh, S. 2021. Thrips tolerance in onions: An examination of thrips population response to different plant size and foliage characteristics, and their effects on bulb weight. MS Thesis, New Mexico State Univ.
• Type: Journal Articles Status: Accepted Year Published: 2022 Citation: Hua, K., Wilson, R., and Dung, J.K.S. 2022. Evaluation of lure crops for the integrated management of white rot (Sclerotium cepivorum) in Allium crops. Plant Disease (accepted with revision).
• Type: Other Status: Published Year Published: 2021 Citation: Regan, K. and B. Nault. 2021. Less is more: Reducing inputs benefits onion production in muck soil. Onion World 37(4): 8-10.
• Type: Other Status: Published Year Published: 2022 Citation: Dung, J.K.S. and Hua, K. 2022. Comparison of fungicides for control of white rot on garlic in Oregon, 2020-2021. Plant Disease Management Reports 16:CF029. doi: 10.1094/PDMR16
• Type: Other Status: Published Year Published: 2021 Citation: Hua, K., and Dung, J.. 2021. Microplot evaluation of Allium lure crops to reduce populations of white rot sclerotia in infested soil. Central Oregon Agricultural Research and Extension Center 2021 Annual Report:31-33.
• Type: Conference Papers and Presentations Status: Awaiting Publication Year Published: 2022 Citation: Hua, K., Qian, Y.P., Qian, M., Wilson, R., and Dung, J.K.S.. 2022. Use of sulfur compounds and Allium lure crops to reduce white rot inoculum in infested soils. Abstract. Phytopathology
• Type: Conference Papers and Presentations Status: Published Year Published: 2022 Citation: Hua, K., Wilson, R., and Dung, J.K.S.. 2022. Use of Alliums as trap crops to reduce white rot inoculum in infested field soil. Oral presentation. 2022 National Allium Research Conference. https://alliumnet.com/wp-content/uploads/2022/05/Schedule_and_Abstracts_NARC_W3008_StR_Feb.21.22.pdf
• Type: Other Status: Published Year Published: 2022 Citation: Hua, K., Wilson, R., and Dung, J.K.S.. 2022. Setting a Trap: Can Early Terminated Allium Trap Crops Reduce White Rot Infestations? White rot Onion World (January 2022):16-18

Progress 09/01/20 to 08/31/21

Outputs
Target Audience:Audiences targeted to receive information generated from this project included onion growers, University extension educators and faculty, professional crop consultants, agri-chemical company representatives, vegetable seed company representatives and the public. Efforts to transfer knowledge about our research have focused on research reports, verbal presentations at stakeholder-based meetings, extension educator-based workshops and on-farm visits. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?Nault:The project involved mentoring a postdoctoral researcher who continues to focus on this research as a major component of her appointment. She presented results from first and second years of the project at the Entomological Society of America Virtual Annual Meeting in November 2020 and Eastern Branch Virtual Meeting of the Entomological Society of America (EB-ESA) in March 2021. She also presented results from both years of the project at an extension meeting held in Elba, NY amongst local onion growers, Cornell Cooperative Extension staff, and agri-chemical reps in August 2021 and in an article published in Onion World Magazine in May 2021, providing experience with extension through both oral and written formats. This experience continues to provide her with opportunities in professional development and science communication opportunity. Pappu: One post-doctoral fellow is receving mentoring who is focusing on evaluating the effect of IYSV on various onion varieties using serological and molecular tools. The post-doc carried out detailed analyses of the genetic diversity of a global collection of IYSV genome sequences to determine the evolutionary patterns of the virus. Havey:A graduate student (Mr. Derek Hunsaker) was supported by this grant and completed the MS degree at the University of Wisconsin-Madison in August 2020. Dung:Objective 3 involves the mentorship of a postdoctoral research associate who coordinates the planning, preparation, execution, and reporting of work related to these efforts. Cramer:Training of graduate students, undergraduate students and interns with regards to trait measurement, instrument use, and data collection. Hosted 2 high school students as interns for 6 weeks to work on research project. Hosted undergraduate student enrolled in the minority ENHANCE program to work on research project. How have the results been disseminated to communities of interest?Nault: The objectives of the project and research progress have been disseminated to onion growers, University Extension educators and faculty, and the public. Efforts to transfer knowledge about our research occurred primarily at a regional twilight meeting, local extension meeting, and through conversations with individual growers cooperating in the project. Pappu: One referred journal publication on the genetic diversity and evolutionary pattners of Iris yellow spot virus was published in Frontiers of Microbiology. Dung: Results were presented at the 2021 Virtual California Garlic and Onion Research Symposium (talk) and the American Chemical Society Spring 2021 Meeting (poster). A webinar was also conducted for the Hort Innovation Onion Fund of Australia. Cramer:Stakeholder field presentation for La Semilla Food Center Farmer Fellowship Training Program. Title: Agroecological Farmers for a Hotter, Drier Future in the Chihuahuan Desert. June 23, 2021. 18 participants What do you plan to do during the next reporting period to accomplish the goals?Nault: Research plans include completing analysis of data from three years of field experiments and publishing these results in a peer-reviewed manuscript and presenting them at the Entomological Society of America National Meeting in November 2021. Additionally, an article will be written to publish in VegEdge, a weekly newsletter produced by the Cornell Cooperative Extension Vegetable Program, servicing vegetable growers throughout Western New York. Dung: Research plans include completing analysis of data from lab, greenhouse, and field experiments and publishing these results in at least two peer-reviewed manuscripts. Results of the project will be shared at the California Garlic and Onion Research Symposium in February 2022, the next National Allium Research Conference meeting (which will be held in conjunction with the annual meeting of the Colorado Fruit and Vegetable Growers Association on February 28 and March 1, 2022), and the 2022 meeting of the American Phytopathological Society Pacific Division.

Impacts
What was accomplished under these goals? A laboratory trial was conducted to evaluate encapsulated garlic oil and diallyl disulfide (DADS), which is easier to handle and apply than previous formulations. Encapsulated garlic oil and DADS were applied to naturally infested soils at a rate equivalent to 2 gal/A either as a dry formulation or as a suspension in water. Both the dry and wet formulations of encapsulated garlic oil and DADS reduced sclerotia counts by approximately 75%, similar to the DADS-treated control. Trap crops were evaluated for use as a source of sclerotial germination stimulants in a field trial. Infested plots were either left fallow (control) or planted to onions; plots with onions were terminated with glyphosate at the second through sixth true leaf stages. Soils were sampled before planting, at termination, and four weeks later. A 24% reduction in sclerotia was observed when onions were terminated at the second leaf stage; however, sclerotia counts were similar to fallow plots by the third leaf termination timing and were greater at all subsequent termination timings. Replicated greenhouse trials conducted in 2020 and 2021 also show similar reductions in sclerotia when onions are terminated at the two-leaf stage. Pyraziflumid is a novel fungicide that exhibited efficacy at suppressing white rot in a field trial conducted in 2020. A garlic field trial was conducted in Madras, OR in 2021 to evaluate Pyraziflumid applied at three rates (3.1, 4.6, and 6.2 oz/A) in-furrow for white rot management. All three rates of Pyraziflumid significantly increased stand counts and plant heights and significantly reduced disease severity compared to the control. At harvest, plots treated with Pyraziflumid at 6.2 oz/A exhibited significantly increased marketable yields compared to the non-treated control. DADS has been demonstrated as an effective biostimulant for white rot sclerotia germination. However, soil incubation experiments suggested that the DADS has interactions with soil exists. Depending on soil type, it was hypothesized that the sulfur compounds could bind to soil particles or be metabolized by microorganisms, reducing the efficiency of DADS on sclerotia germination. Therefore, new experiments were conducted to encapsulate DADS and garlic oil with β-cyclodextrin (β-CD) to protect them from reacting with soil. In addition, encapsulation can protect the DADS and garlic oil against oxidation, heat and light-induced degradation, and evaporation. The micro-capsules are much easier to handle than the liquid form. The maximum inclusion efficiency was achieved by co-precipitating DADS/garlic oil with β-cyclodextrin at 15:85 ratio (w/w). Oil analysis showed that the garlic oil was successfully encapsulated with greater than 90% powder recovery. In addition, the lab sclerotia germination study using encapsulated DADS and garlic micro-capsules showed a 75% reduction in sclerotia counts, as effective as the DADS solution treatment. In New York, we have evaluated onion thrips densities and marketable bulb yield in response to reduced rates of NPK fertilizer and either weekly insecticide applications or applications made only after an action threshold of 1 thrips larva/leaf has been reached. We have compared a grower's typical rate of NPK fertilizer, half that rate, and no fertilizer, each managed with either an action threshold-based insecticide program or a weekly insecticide program. This experiment has been replicated in four fields in 2019, eight fields in 2020, and nine fields in 2021. Data collection are ongoing for the current 2021 season. Although onion thrips were significantly lower in plots receiving a weekly insecticide application than those following an action-threshold based insecticide program, they were kept below the economic injury level of 2.2 thrips larvae per leaf on average. This indicates that action threshold programs were successful at controlling onion thrips densities to an acceptable level. Fertilizer rate had no significant effect on onion thrips densities and did not provide any additional control beyond that provided by insecticide application. In New York muck onion systems, neither fertilizer rate nor insecticide spray frequency significantly affected onion yield. Thus, action threshold-based insecticide programs were successful in this system. There is great potential for growers to reduce insecticide inputs by following action-thresholds and to reduce fertilizer applications without compromising onion yield. In Oregon, the following parameters were evaluated: onion thrips densities and marketable bulb yield in response to nitrogen fertilization rates, and weekly insecticide applications, insecticide applications made only after an action threshold of 1 thrips larva/leaf has been reached, or no insecticide applications. To determine fertilization levels, weekly soil and tissue sampling for nutrients wasconducted. Data collection are ongoing for the current 2021 season. The experiment was replicated in 2019 and 2020. In 2020 trial conducted in Oregon, no differences were observed in thrips populations or yield among the fertilization treatments. Results showed the importance of the judicious use of insecticides for thrips management. As in the New York research, action threshold-based insecticide programs were successful in the Oregon system and there are opportunities for growers to reduce their insecticide and nitrogen applications and save 2 - 4% of their input costs without reducing yields. For objective 2 from the 2020 evaluation, plants of 'Stockton Early Yellow' possessed more juvenile and total thrips at 9 and 11 weeks after transplanting (WAT) than plants of 4 NMSU germplasm lines when averaged over irrigation treatments. There were no differences in thrips number per plant between the two irrigation treatments. Thrips number per plant increased from 9 to 13 WAT and decreased afterwards for all entries. At each observation date, plants of all entries exhibited a similar number of leaves, plant height, and sheath diameter when grown using either irrigation treatment. When averaged over entries, there were no differences in photosynthetic measurements between irrigation treatments at each observation date. At 11, 13, and 15 WAT, plants of 'Stockton Early Yellow' exhibited a lower carbon assimilation (CA) rate and more severe Iris yellow spot (IYS) than plants of all other 4 entries. For each entry, CA rate decreased from 11 to 17 WAT. Plants of NMSU 12-238 produced bulbs of the largest size while plants of 'Stockton Early Yellow' produced the smallest bulbs. In Oct. 2020, 'NuMex Freedom' onion bulbs and seed were placed in the field as in the previous year to promote thrips spread throughout the field. In Jan. 2021, seed of 29 NMSU germplasm lines and 'Stockton Early Yellow', an IYS-susceptible cultivar was sown in flats. Onion plants were grown in the greenhouse and field environments in 2021 and leaves sampled to determine types and amounts of epicuticular waxes on foliage. Onion plants with semi-glossy leaves showed resistance to thrips feeding damage. Most plants had relatively low amounts of total wax, however a population was developed with semi-glossy foliage, but with total wax equal to or exceeding waxy susceptible plants. Seed is being increase of this synthetic population for release to stakeholders. Seed of two inbred lines (B5336 A&B and B5351C) were formally released by the USDA to stakeholders. The hybrid produced by crossing of these two inbreds (B5336A x B5351C) is named 'USDA-Maia' and is the first semi-glossy hybrid onion adapted for production across the Great Lakes Region and Pacific Northwest. 'USDA-Maia' shows resistance to pink root, Fusarium basal rot, and thrips feeding damage, and produces well storing onion bulbs with yellow skins and relatively low pungency.

Publications

• Type: Journal Articles Status: Awaiting Publication Year Published: 2021 Citation: Tabassum, A., R.V. Shunmugiah, Y. Zhai, Romana Iftikhar, C.A. Olaya and H.R. PappuViruses without Borders: Global Analysis of the Population Structure, Haplotype Distribution, and Evolutionary Pattern of Iris yellow spot orthotospovirus (Family Tospoviridae, Genus Orthotospovirus). Frontiers in Microbiology.
• Type: Journal Articles Status: Published Year Published: 2021 Citation: Greenway, G., N. Kamal, S. Shahabeddin Nourbakhsh, and C.S. Cramer. 2021. Estimating potential changes in costs and returns from use of a partially onion thrips-resistant cultivar and action-based spray thresholds in Idaho and Eastern Oregon. Southwestern Entomologist. 46:349-356. https://doi.og/10.3958/059.046.0206.
• Type: Journal Articles Status: Published Year Published: 2021 Citation: Kamal, N. S. Shahabeddin Nourbakhsh, and C.S. Cramer. 2021. Reduced Iris yellow spot symptoms through selection within onion breeding lines. Horticulturae 7:12.
• Type: Other Status: Published Year Published: 2021 Citation: Hua, K. and Dung, J. 2021. Use of Alliums as Trap Crops to Reduce White Rot Inoculum in Infested Soils. Central Oregon Agricultural Research and Extension Center 2020 Annual Report:19-20.
• Type: Other Status: Published Year Published: 2021 Citation: Hua, K., and Dung, J. 2021. Comparison of Fungicides for Control of White Rot on Garlic in Oregon, 2019-2020. Central Oregon Agricultural Research and Extension Center 2020 Annual Report:17-18.
• Type: Journal Articles Status: Published Year Published: 2021 Citation: Hua, K., and Dung, J.K.S.. 2021. Comparison of fungicides for control of white rot on garlic in Oregon, 2019-2020. Plant Disease Management Reports 15:V032.
• Type: Other Status: Published Year Published: 2021 Citation: Regan, K. and B. Nault. 2021. Less is More: Reducing Inputs Benefits Onion Production in Muck Soil. Onion World Magazine, May-June 2021 Issue.
• Type: Journal Articles Status: Published Year Published: 2021 Citation: Havey, M.J., D. Hunsaker, and E.D. Munaiz. 2021. Genetic analysis of the unique epicuticular-wax profile of Odourless Greenleaf onion. J. Amer. Soc. Hort. Sci. 146:118-124. https://doi.org/10.21273/JASHS05024-20
• Type: Journal Articles Status: Published Year Published: 2021 Citation: Iglesias, L., M.J. Havey, and B.A. Nault. 2021. Potential for managing onion thrips (Thrips tabaci) in organic onion production using multiple IPM tactics. MDPI Insects 12(3):207. https://doi.org/10.3390/insects12030207
• Type: Other Status: Published Year Published: 2021 Citation: Chitturi, Anitha, Erik B. G. Feibert, Kyle Wieland, Ian Trenkel, Alicia Rivera, and Stuart Reitz. 2021. Management of Onion Thrips with Threshold-Based Insecticide Applications and Reduced Nitrogen Fertility2020. In: Reitz, S. R. (ed) Oregon State University Malheur Experiment Station Annual Report 2020, Department of Crop and Soil Science Ext/CrS 165: 170-181. https://agsci.oregonstate.edu/system/files/r_ipm_report_2020.pdf
• Type: Other Status: Published Year Published: 2021 Citation: Murray, Katie, Stuart Reitz, and Paul Jepson. (2019). An Integrated Pest Management Strategic Plan for Treasure Valley Onions: Oregon and Idaho. Corvallis, OR, Oregon State University Extension Service. https://catalog.extension.oregonstate.edu/sites/catalog/files/project/pdf/em9254.pdf

Progress 09/01/19 to 08/31/20

Outputs
Target Audience:Audiences targeted to receive information generated from this project included onion growers, University extension educators and faculty, professional crop consultants, agri-chemical company representatives, vegetable seed company representatives and the public. Efforts to transfer knowledge about our research have focused on verbal presentations at stakeholder-based meetings, extension educator-based workshops and on-farm visits. Changes/Problems:State and University restrictions related to COVID-19 greatly affected our ability to showcase our field research in demonstration plots with growers in summer 2020. What opportunities for training and professional development has the project provided?For Objective 1 in NY, the project involved mentoring a postdoctoral research associate who continues to focus on this research as a major component of her appointment. She presented first-year results of our project at the Annual Meeting of the Entomological Society of America in November 2019 as well as co-presented them at the Empire State Producer's EXPO in January 2020. COVID has disrupted our plans to demonstrate 2020 field results to growers. Nevertheless, working on growers farms and communicating results from the project continue to provide her with opportunities in professional development and science communication opportunity. A graduate student (Mr. Derek Hunsaker) at the University of Wisconsin was supported by this grant and successfully completed the MS degree in August 2020. Objective 2 involves mentorship of one post-doctoral associate who is working on testing the response of various onion cultivars for IYSV infection by determining the relative levels of the virus and viral RNA using ELISA and qPCR. Objective 3 involves the mentorship of a postdoctoral research associate who is focused on this project and coordinates the planning, preparation, execution, and reporting of work related to these efforts. Prior to the COVID-19 pandemic, she visited grower fields to survey for disease, take samples, and learn about agricultural operations related to Allium production. She co-presented results from her first year of research at the 2020 California Garlic and Onion Research Symposium in Tulare, CA and the American Phytopathological Society's 2020 Plant Health Meeting. How have the results been disseminated to communities of interest?Results of this project have been disseminated to onion growers, University Extension educators and faculty, and the public only via presentations at meetings. Additional conference and Extension presentations, field visits, and workshops will occur as soon as COVID restrictions subside. Research results and updates have been communicated to the White Rot Scientific Advisory Committee via bi-monthly video conferences. A white rot webinar will be presented August 21, 2020 for a brown bag seminar series hosted by the Washington State University Mt. Vernon NW Washington Research and Extension Center. What do you plan to do during the next reporting period to accomplish the goals?In NY, research plans for next reporting period include repeating the experiments in onion growers' fields. Results of the project will be shared at the Empire State Producer's EXPO in January 2021, Eastern Branch Meeting of the Entomological Society of America in February 2021, and regional meetings throughout NY in February and March 2021. A field day will also be planned for the summer of 2021 to share the results of the research project to our stakeholders at one of our on-farm research sites. The website of the Brian Nault Laboratory will be updated with results from both years of the project and general information on onion production using less fertilizer and onion thrips management. New elite inbredand synthetic populations with semi-glossy foliage will be released in late 2020 or early 2021 to stakeholders. Research plans for Objective 3 in 2020-2021 include repeating trap crop greenhouse and field experiments in central Oregon and California, and repeating fungicide efficacy trials. The Fresno field trial will be re-sampled in late August and planted to garlic in October to mid-November.Efforts to microencapsulate germination stimulants for improved application and efficacy will continue. Further research will study the release of volatile sulfur compounds from the encapsulation complex in different soils and effects on sclerotia germination. Results of the project will be shared at the Central Oregon Farm Fair and Trade Show in February 2021, the California Garlic and Onion Research Symposium in February 2021, and regional meetings throughout the U.S. Pacific Northwest in 2021.

Impacts
What was accomplished under these goals? In New York,various rates of fertilizer and insecticide spray programs were evaluated for their impact on onion thrips infestations and onion bulb yield in commercial muck onion fields. Four fields were selected and growers applied three different treatments of N-P-K within 0.1 to 0.3 acre blocks. Treatments included a standard fertilizer rate (N= 89-125 lb/acre; P= 100-150 lb/acre; K= 145-200 lb/acre), half the standard rate, and no fertilizer. Across all fertilizer treatments, insecticides were applied to manage thrips following an action threshold of 1 thrips per leaf. Within each fertilizer treatment, a subplot was created such that it would receive an insecticide application every week (i.e., weeks the grower skipped spraying because the action threshold was not reached in the field, we treated the subplot with an insecticide using a backpack sprayer). Results indicated that onion thrips infestation levels were not impacted by fertilizer treatment. Onion thrips densities were significantly lower in plots treated weekly with insecticides than in portions of the field only sprayed following the action threshold. However, all thrips densities were below the economic injury level in both treatments and 2-5 fewer sprays were made in the action threshold treatment. Onion bulb yield did not differ across the three fertilizer treatments. Surprisingly, bulb yield in plots that received the full standard rate of fertilizer and half this rate had the same yield as plots that were not fertilized. Onion plants were grown in the greenhouse and field environments in 2020 and leaves sampled for analyses of types and amounts of epicuticular waxes on foliage. Populations included four commercial onions used by Dr. Brian Nault for thrips studies in NY (Alisa Craig, Avalon, Bradley, Rossa di Milano, and a USDA experimental hybrid B5336 x B5351 with semi-glossy foliage). Alsoevaluated were USDA breeding lines and an experimental synthetic population, all with semi-glossy foliage. Most of the semi-glossy breeding lines had relatively low amounts of total wax, however the synthetic population was uniformly semi-glossy with individual plants accumulating total wax equal to or exceeding the waxy control. These plants will be selected, progenies produced, and used to produce new semi-glossy lines with high amounts of total wax and still retain the semi-glossy phenotype associated with thrips resistance. Individual bulb weight, height, and diameter evaluated in 2019 was greater when entries were grown using the well watered treatment (WWT) (not to exceed 30% managed allowed depletion [MAD] based upon crop evapotranspiration [ET]) than when they were grown using the water limited treatment (WLT) (50% MAD). For both irrigation treatments, Rumba produced smaller bulbs on average than all other entries. Onions grown using the WWT in 2019 had higher carbon assimilation (CA) rates than onions grown using the WLT at 12 and 14 weeks after transplanting (WAT), suggesting that decreased amounts of water may decrease CA rates. Rumba plants exhibited a reduced CA rate at 8, 10, 12, and 14 WAT when they were grown using the WLT as compared to the WWT. NMSU 12-236 plants exhibited a reduced CA rate at only 12 and 14 WAT when they were grown using the WLT as compared to the WWT. The difference between the 2 entries would indicate that 12-236 plants were more tolerant of water stress than Rumba plants. At 12, 14, and 16 WAT, all entries in 2019 exhibited a lower leaf area index (LAI) for plants grown using the WLT as compared to plants grown using the WWT. In Oct. 2019, 'NuMex Freedom' onion bulbs and seed were placed in the field as in the previous year to promote thrips spread throughout the field. In Jan. 2020, seed of 4 NMSU lines and Stockton Early Yellow, an Iris yellow spot (IYS) susceptible cultivar was sown in flats. Two row of plants were transplanted in Mar. to 3.3 m long field plots. Field design and irrigation management were the same as the previous year. On 8 May, irrigation treatments were initiated. Ten plants/plot were randomly-selected for data measurements. Starting on 12 May and every 2 weeks after, plant height, leaf number and sheath diameter were measured. A portable photosynthesis system was used to determine net photosynthesis/CA rate, stomatal conductance and transpiration rate on 5 plants/plot. These measurements were repeated for 4 additional times 2 weeks apart. Starting on 18 May and 4 additional times 2 weeks apart, adult and juvenile thrips were counted. On 3 June, IYS symptom severity was rated on a scale of 0 to 4 and repeated for 3 additional times 2 weeks apart. On the same dates LAI was measured using a photosynthetically active radiation ceptometer. Once a plant matured, the plant was harvested, the date of maturity, bulb height, diameter, and weight was recorded. Individual bulbs that exhibited fewer IYS symptoms were selected from plots. Data for measured traits are in the process of being analyzed or collected. For the evaluation of sulfur compounds for use as germination stimulants, diallyl disulfide (DADS), isopropyl disulfide, dipropyl disulfide (DPDS), and dimethylsulfoxide were evaluated alone at 0.1, 1, and 2 gal/A rates and in all two-, three-, and four-way combinations (1 gal/A each) in growth chamber trials. All individual compounds significantly reduced sclerotia counts in soil, with the lowest sclerotia counts recorded in DADS (1 and 2 Gal/A) or DPDS (2 Gal/A) treated soils. Additive or synergistic effects were not observed when sulfur compounds were combined. Novel fungicides were screened for white rot control in a garlic field trial. Pyraziflumid, Pydiflumetofen, Benzovindiflupyr were evaluated as in-furrow applications and compared to Tebuconazole, Penthiopyrad, and a non-treated control. All of the fungicides increased stand counts and plant heights and reduced disease severity in April. By June, plots treated with Tebuconazole, Pyraziflumid, and Pydiflumetofen exhibited reduced disease severity. Tebuconazole and Pyraziflumid significantly increased marketable yields. For the use of trap crops as germination stimulants, seeds of white-, red-, sweet- or bunching onion were sown in pots filled with white rot-infested soil. Sclerotia counts were significantly reduced in all trap crop treatments at 3- and 7 weeks post-emergence (wpe) termination, but only in the red onion trap crop treatment at 11 wpe termination. At 4 weeks after crop termination, sclerotia levels remained unchanged when seedlings were terminated at 3 wpe, but sclerotia counts increased in soil cultivated with bunching, white, or sweet onions and terminated at 11 wpe. Investigations into new sources and formulations of germination stimulants included natural sources of sulfur compounds were evaluated for sclerotia germination. The results showed that garlic juice, garlic powder, and raw onion all could stimulate sclerotia germination. Germination efficiency of pure garlic oils distilled from California Early and Late varieties was similar to DADS. Over 100 garlic varieties have been screened to identify germplasm with high contents of DADS that could be planted for the production and distillation of biostimulants. The fate of volatile organic sulfur compounds when applied to the soil was studied. It was found that, depending on the type of soils, organic matter, and soil microorganisms, DADS can bind to soil or be metabolized by microorganisms. In either case, it reduces the efficiency of germination stimulation. Efforts were made to encapsulate DADS and garlic oil with β-cyclodextrin to protect volatiles against environmental and biological degradation, and to allow for slower release and easier application in the field. Garlic oil was successfully encapsulated with β-cyclodextrin and > 90% powder recovery. DADS was the major constituent of garlic oil encapsulated (63% of the total). Encapsulation was also successful with pure DADS.

Publications

• Type: Journal Articles Status: Published Year Published: 2020 Citation: Munaiz, E.D., P.A. Townsend, and M.J. Havey. 2020. Reflectance spectroscopy for non-destructive measurement and genetic analysis of amounts and types of epicuticular waxes on onion leaves. Molecules 25:3454; doi:10.3390/molecules25153454
• Type: Conference Papers and Presentations Status: Accepted Year Published: 2020 Citation: Hua, G.K.H., and Dung, J.K.S. 2020. Use of Alliums as trap crops to reduce white rot inoculum in infested field soil. Abstract. American Phytopathological Society Plant Health 2020 Meeting (accepted).

Progress 09/01/18 to 08/31/19

Outputs
Target Audience:Updates on research progress on resistances and control strategies for thrips, IYSV, and white rotwere presented at the joint research conference of the National Onion Association (main stakeholder group for onion in North America), the National Allium Research Conference (NARC), and the International Allium Research Conference (IARS), attended by growers, processors, shippers, and research personnel. The target audience for this research is the numerous individuals and companies involved in the US Allium industries. These interested parties include growers, shippers, handlers, brokers, dealers, salespersons, breeders, and researchers. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?For USDA-ARS, acooperative agreement was established with the University of Wisconsin and agraduate student was hired to carry out research on types and amounts of epicuticular waxes on thrips resistant and susceptible onions. Training of undergraduate students and interns with regards to trait measurement, instrument use, and data collection. At Oregon State University, a Postdoctoral Scholar was hired to carry out research on white rot biology, epidemiology, and integrated management. Undergraduate students were also trained on methodologies related to experimental design, microbiological techniques, disease assessment, data collection, and data analyses. How have the results been disseminated to communities of interest?Updates provided at joint NOA/NARC/IARS symposium. A presentation was made at the 2019 annual meeting of Multistate Research Project W3008: Integrated Onion Pest and Disease Management on July 24, 2019 regarding research work on onion thrips. A presentation was made on February 11, 2019, at the California Garlic and Onion Symposium in Tulare, CA updating the California Allium industry on white rot research progress and outcomes. There were approximately 60 attendees consisting of growers, packers, crop advisors, and chemical representatives. What do you plan to do during the next reporting period to accomplish the goals?Evaluations of epicuticular waxes and thrips resistance in field plots over years. 3. Lab experiments will be conducted to test four compounds (DADS, DMSO, DPDS, and IPDS) individually and in all possible 2-, 3-, and 4-way combinations for their ability to induce sclerotia germination. SPME-GC-MS will be used to monitor effective volatile sulfur compound concentration in the soils. Experimental field sites in Madras, OR and Tulelake, CA were infested and planted to garlic and onion, respectively, to promote inoculum production for 2019-2020 field trials. A microplot trial will be established in September 2019 at the Central Oregon Agricultural Research and Extension Center in Madras to evaluate novel in-furrow fungicides (e.g. Solatenol, Adeppidyn, Pyraziflumid) for white rot suppression in garlic with and without sclerotial germination stimulants. Field plots will be established and treated at a commercial site near Fresno, CA in January 2020 and at the Irrigated Research and Extension Center in Tulelake, CA in April 2020 to evaluate novel in-furrow fungicides for white rot suppression in garlic and onion, respectively, with and without sclerotial germination stimulants. Soil samples will be collected from all field experimental plots for volatile sulfur analysis. Volatile sulfur compounds exuded by garlic roots in field growth periods will be studied in both Madras, OR and Tulelake, CA.

Impacts
What was accomplished under these goals? Several onion breeding lines and germplasm were screened for thrips feeding and resistance to IYSV. Cv. Rumba had higher thrips damage and IYSV incidence compared to breeding lines. Selected volatiles were evaluated for their effect on scelrotia of white rot fungus. DADS was found to be most effective. Allyl isothiocyanate, which is available as a commercial biofumigant product, significantly reduced sclerotia viability (0% viable) compared to the control (96% viable) and may provide another option for reducing white rot inoculum in infested fields. In October 2018, onion bulbs were placed on the first and last bed of the study and at the front and back borders of the field study. In addition, seed of 'NuMex Freedom' was sown at the same time on every seventh bed to ensure that thrips are spread throughout the field the following year. On 7 January 2019, seed of four NMSU germplasm lines and 'Rumba', an IYS-susceptible cultivar was sown in flats at the Fabian Garcia Science Center in Las Cruces, NM. Plants were transplanted to 3.3 m long field plots on 5-11 March 2019 with 2 rows of plants per plot and 7.5 cm between plants within the row. Plants were irrigated using drip irrigation tape that was placed 10 cm beneath the surface of the bed and centered on the bed. The field was arranged using a split-plot design with irrigation as whole plots and selections as subplots. Each whole plot was replicated three times and within whole plots, selections were arranged in a RCBD with four replications. On 21 April 2019, irrigation treatments of well-watered (not to exceed 30% managed allowed depletion [MAD] based upon crop evapotranspiration [ET]) and water-limited conditions (50% MAD based upon crop ET) were initiated. Total available water for the particular soil type was determined for a 0.3 m and 0.5 root depth. Ten plants were randomly-selected from each plot and identified with a plastic label. Starting on 7 May 2019 and every two weeks afterwards, plant height, leaf number, and sheath diameter were measured for each of the ten plants. In addition, a portable photosynthesis system was used to make direct gas exchange measurements and calculations including net photosynthesis/CO2 assimilation rate (A), stomatal conductance (gsw), and transpiration rate (E) on five plants per plot. These measurements were repeated for four additional times two weeks apart. On the same dates, leaf area index (LAI) of the plants within each plot was measured using a photosynthetically active radiation (PAR)/LAI ceptometer. Starting on 8 May 2019 and four additional times two weeks apart, the number of adult and juvenile thrips were counted from each of the ten plants from each plot. Leaf samples were collected from five plants per plot and sent to Michael Havey at the University of Wisconsin-Madison for epicuticular wax analysis and determination. At the time that leaf samples were taken, leaf color was quantified using a chromameter. On 5 June 2019, the severity of Iris yellow spot symptoms was rated for each of the ten plants on a scale of 0 to 4, where 0 = no symptoms; 1 = 1-2 small lesions per leaf; 2 = more than 2 medium-sized lesions; 3 = lesions coalescing on more than 25% of the leaf tissue; 4 = more than 50% leaf is dead. These ratings were repeated for two additional times two weeks apart. At the same times, leaf samples were collected from each of the ten plants and sent to Hanu Pappu at Washington State Univ. to determine the presence and amount of Iris yellow spot virus particles found within the tissue. Once a plant matured, the plant was harvested, the date of maturity recorded and bulb height, diameter, and weight was measured. At bulb maturity, individual bulbs, that exhibited fewer IYS disease symptoms, were selected from plots. Once all bulbs in the plot were mature, bulbs were harvested, counted and weighed. At 8 and 10 weeks after transplanting, plants of 'Rumba' possessed more juvenile and total thrips than plants of the four NMSU germplasm lines when averaged over irrigation treatments. At 12 weeks, plants of 'Rumba' grown under the deficit irrigation treatment had fewer juvenile and total thrips than plants of 'Rumba' grown under the well watered treatment. For both irrigation treatments, plants of 'Rumba' exhibited more thrips than plants of the NMSU germplasm lines when thrips were counted at 12 weeks. After 12 weeks, the number of thrips per plant decreased for all entries except for NMSU 12-337. At 16 weeks after transplanting, plants of NMSU 12-337 possessed more juvenile and total thrips than plants of other entries. This difference was mainly due to the maturity of plants of NMSU 12-243, 12-236, and 12-238, the poor performance of 'Rumba' plants, and the actively growing plants of NMSU 12-337. When averaged over all entries, plants grown under the well watered treatment exhibited a greater number of leaves, plant height, and sheath diameter than plants grown under the deficit irrigation treatment from 10 to 16 weeks after transplanting. At 12, 14, and 16 weeks, plants of 'Rumba' exhibited more severe Iris yellow spot disease symptoms than plants of all other four entries. Data for other traits and characters measured are still being collected or in the process of being analyzed. 3. Eight treatments (allyl isothiocyanate-AITC, diallyl disulfide-DADS, diethyl disulfide-DEDS, dimethyl disulfide-DMDS, dimethyl sulfoxide-DMSO, dimethyl trisulfide-DMTS, dipropyl disulfide-DPDS, and isopropyl disulfide-IPDS) were applied to 250 cc of naturally-infested soil at a rate of 10 gal/acre. All treatments significantly (P=0.0002) reduced sclerotia populations compared to the non-treated control. DADS was the most effective, reducing sclerotia populations by 66%. IPDS and DPDS reduced sclerotia by 48% and 46%, respectively, and were not significantly different from DADS; these compounds may be suitable alternatives for DADS. Preliminary results indicate a synergistic effect of dimethyl sulfoxide with several of the treatments, providing similar or enhanced control at lower rates of biostimulants (0.1 to 1 gal/A) than when the treatments were used alone at higher rates. Allyl isothiocyanate, which is available as a commercial biofumigant product, significantly reduced sclerotia viability (0% viable) compared to the control (96% viable) and may provide another option for reducing white rot inoculum in infested fields. The diallyl disulfide in soil released from garlic was quantified by using the headspace solid phase microextraction-gas chromatography-mass spectrometry (SPME-GC-MS) method. Two varieties of garlic (California Early and California Late) were planted (10 cloves/container) in the greenhouse and 5 g of rhizosphere soil were collected from each container at approximately 30, 50, 70, and 100 days after planting. The amount of DADS detected in the rhizosphere ranged between 6 and 84 ppb, indicating that low levels of DADS are required for sclerotia germination and infection around the root zone. A laboratory experiment is currently underway to determine the longevity and fate of DADS in different field soils over time.

Publications

• Type: Journal Articles Status: Published Year Published: 2019 Citation: Singh, N. and C.S. Cramer. 2019. Improved tolerance for onion thrips and Iris yellow spot in onion plant introductions after two selection cycles. Horticulturae 5:18. doi 10.3390/horticulturae5010018.
• Type: Conference Papers and Presentations Status: Other Year Published: 2019 Citation: Scott, J.C., Jeliazkova, E., Cheng, Q., Qian, Y., Qian, M., and Dung, J.K.S. 2019. Evaluation of alternatives to soil fumigants and diallyl disulfide for the management of white rot. 2019 National Allium Research Conference. Hunsaker, D., R. Groves, and M.J. Havey. 2019. Variation for Epicuticular Waxes across Diverse Onion Germplasm. 2019 National Allium Research Conference. Munaiz, E.D., S. Damon, R.L. Groves, and M.J. Havey. 2019. Leaf waxes and thrips resistance. 2019 National Allium Research Conference.
• Type: Other Status: Published Year Published: 2018 Citation: Dung, J. and Scott, J. 2018. Microplot evaluation of sclerotia germination stimulants for white rot control in garlic. Central Oregon Agricultural Research and Extension Center 2018 Annual Report: 26-28.
• Type: Other Status: Published Year Published: 2019 Citation: Pappu, H.R. 2019. Screening for resistance to Iris yellow spot virus: An update. Presentation made a the 2019 Annual Washington State Onion Field Day, Prosser, WA. August 29, 2019.
• Type: Conference Papers and Presentations Status: Published Year Published: 2019 Citation: Tabassum, A., Y. Zhai, R. Iftikhar, S.V. Ramesh, and Pappu, H.R. 2019. Genetic diversity of Iris yellow spot virus. International Conference on Advances in Plant Virology. Rome, Italy. October 29-31, 2019.