Source: PENNSYLVANIA STATE UNIVERSITY submitted to
IDENTIFICATION OF FACTORS ASSOCIATED WITH ONION BACTERIAL DISEASES TO FACILITATE THE DEVELOPMENT OF AN INTEGRATED PEST MANAGEMENT PROGRAM
Sponsoring Institution
National Institute of Food and Agriculture
Project Status
TERMINATED
Funding Source
Reporting Frequency
Annual
Accession No.
0225017
Grant No.
2011-34103-30711
Project No.
PEN04433
Proposal No.
2011-00535
Multistate No.
(N/A)
Program Code
QQ.NE
Project Start Date
Aug 15, 2011
Project End Date
Aug 14, 2014
Grant Year
2011
Project Director
Gugino, B.
Recipient Organization
PENNSYLVANIA STATE UNIVERSITY
208 MUELLER LABORATORY
UNIVERSITY PARK,PA 16802
Performing Department
Plant Pathology & Environmental Microbiology
Non Technical Summary
During the past 5 to 10 years, bacterial bulb decay, caused by a number of different bacterial pathogens, has assumed much greater importance in the Northeast region. In PA and NY, annual losses range from 5 to 40%. However, these losses are variable, between fields and within the same field; in many cases the full extent of disease losses is not evident until at or post-harvest. In part this is because bacterial bulb decay often affects only a single internal scale while outer scales remain firm, such infected bulbs are virtually impossible to detect. Such onion are shipped and consequently rejected, which often results in entire loads being dumped, despite only a small percentage of bulbs being infected. In order to develop an integrated pest management plan it is important to understand what factors are associated with increased bacterial disease. One key factor is identifying where the bacterial pathogens are coming from (transplants, weeds, soil, etc.) so that management efforts can be directed towards excluding or reducing the pathogen from the field. For example, if we learn that bacteria present on the surface of visibly healthy onion transplants are associated with disease losses observed later in the growing season then research could be directed towards determining the most effective way to obtain pathogen-free transplants. Another potential factor is onion thrips, the most common insect pest in onion fields in the Northeast region and worldwide. The damage caused during feeding creates a wound or opening for the bacteria to get into the plant. Additionally, observations from grower fields and preliminary on-farm research trials in PA and NY suggest that excessive nitrogen fertility is also correlated with greater losses from bacterial diseases. By gaining a better understanding of the factors contributing to bacterial diseases in commercial production fields we will be able to fine-tune current management recommendations to reduce the likelihood of severe losses from bacterial pathogens as well as facilitate additional research trials to develop more targeted research-based management plans. The ultimate goal of this project is to develop knowledge-based, sustainable and cost-effective management strategies for bacterial diseases of onion in the Northeast and in other relevant production regions. In the long-term, success of the project will be reflected in reduced economic losses from bacterial diseases and reduced reliance on copper-based fungicide inputs through the integration of cultural management practices that include the optimization of nitrogen inputs for maintaining yields, minimizing thrips-induced injury and protecting plantings against wind-induced injury.
Animal Health Component
(N/A)
Research Effort Categories
Basic
50%
Applied
50%
Developmental
(N/A)
Classification

Knowledge Area (KA)Subject of Investigation (SOI)Field of Science (FOS)Percent
2121451116050%
2161451116050%
Goals / Objectives
During the past 5 to 10 years, bacterial bulb decay has assumed much greater importance in the Northeast region. In PA and NY, annual losses range from 5 to 40%. However, disease losses are variable, both among and within fields; in many cases the full extent of disease losses is not evident until harvest or thereafter. The objective of this project is to identify factors associated with bacterial disease incidence in commercial onion fields in order to facilitate the development of an integrated pest management program for onion bacterial diseases in the Northeast region. We hypothesize that infested transplants, weeds, soil, and thrips are sources of bacterial inoculum in commercial fields. Furthermore, we hypothesize that injury from thrips, wind whipping and high levels of soil nitrogen contribute to bacterial disease incidence and severity. These factors were selected for evaluation based on preliminary evidence of their association with the incidence and severity of onion bacterial diseases in PA and/or NY. Using intensive small plot surveys of commercial fields as well as several replicated on-farm component research trials we will determine the relationship of these factors to onion bacterial disease incidence and severity and test our hypotheses. The goal of this proposal is to identify important relationships and utilize such knowledge to fine-tune recommendations with regard to important sources of bacterial pathogens, nitrogen, thrips and weed management as well as facilitate additional trials to develop more targeted research-based management plans to reduce the likelihood of severe losses from onion bacterial pathogens.
Project Methods
To identify factors related to bacterial disease incidence in commercial onion fields, an intensive field survey will be conducted in 25 to 30 fields in PA and the same number in NY in each of two years for a total of 50 to 60 fields per year and 100 to 120 fields over the course of the project. In each field, three plots approximately 1 bed wide (4 to 6 rows per bed) by 30 ft long (240 onions per plot or more for direct seeded plots) will be flagged and GPS coordinates recorded. Plots will be managed by the grower using his or her standard practices. Commercial fields will be selected to reflect a range of historical problems with bacterial decay from none or minimal to extensive losses. Variability between fields will be needed to relate the described independent variables to the dependent variable (bacterial disease incidence and severity). In PA, the focus will be fields grown from cv. Candy transplants on plastic mulch. In NY, primarily muck land fields direct-seeded with the cvs. Red Bull, Mercury, Red Wing and Red Zepelen will be studied however several transplants fields may be included as well. These reflect the dominant production systems in each state. The three plots within each field will be located to capture maximum potential variability within the field (e.g. in PA top and bottom of slope, wooded border, etc.; in NY, the edges and middles of the fields). From each plot or field, data regarding the bacteria associated with onion transplants, weeds, thrips and soil will be collected and evaluated for pathogenicity. Soil and or plant nitrogen content will be measured at three critical time points during the growing season and yield and disease assessments will be made during the season and or at harvest. A sub-sample of 75 to 100 onion bulbs will be dried, stored and graded after months to reflect typical production practices. Field management history and microclimate data for each field will be collected throughout the season. Data will be analyzed using an analysis of covariance (ANCOVA) in PROC MIXED in SAS v. 09.2 to test whether the independent variables measured had an effect on bacterial disease incidence and severity (dependent variable) as well as yield. In addition, a series of replicated on-farm small plot trials will be conducted to compliment the small-plot intensive surveys to fine-tune our understanding of the relationships between bacterial disease and nitrogen fertility, thrips and wind-induced injury. Based on the results of the intensive field survey and replicated on-farm trials, the PIs anticipate being able to fine-tune recommendations with regard to important sources of bacterial pathogens, nitrogen, thrips and weed management recommendations as well as facilitate further research trials to develop more targeted research-based management plans. Research results will be disseminated to onion producers and interested stakeholders via one-on-one interactions, twilight, local and regional meetings and newsletter articles. Also, the extensive on-farm research itself will increase grower awareness about onion bacterial diseases and the need to manage them using an integrated strategy.

Progress 08/15/11 to 08/14/14

Outputs
Target Audience: All onion growers in the Northeast region stand to benefit from this project. Smaller scale growers sell primarily sweet onions, through local produce auctions and direct markets. These lucrative markets pay $1.00/lb or more for jumbo and colossal sized bulbs. Reducing losses from bacterial diseases will directly and immediately impact farm profitability. As we succeed in developing an IPM approach to manage bacterial bulb decay that relies heavily on cultural practices, current growers will sustain or increase their acreage and more small-scale diversified vegetable growers will start growing onions, thus building the fresh market onion industry in the Northeast. Reduced incidence of bacterial diseases, especially when it is undetectable in the bulb, will greatly decrease loads being rejected and the dumping of healthy onions along with the rotten ones for large-scale muck onion growers. The results of this research would also be applicable for states such as New Jersey who are looking to build local production to support a processing industry that traditionally ships onions form the Pacific Northwest. The general public will benefit from having affordable locally-grown onions of superior quality available to the year round. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided? Understanding the environmental and on-farm management factors that are contributing to onion yield losses associated with bacterial disease incidence was the focus of Emily E. Pfeufer’s Ph.D. research in the Department of Plant Pathology and Environmental Microbiology at Penn State. Dr. Pfeufer successfully defended and graduated in August 2014. A research poster presentation given by Emily Pfeufer titled “Common weeds as potential sources of bacterial pathogen inoculum causing onion bulb rots in Pennsylvania” resulting from this research project was awarded 1st place in the Biological Sciences Division at the 2013 Penn State Gamma Sigma Delta Research Competition and 2nd place in the 2013 Penn State Graduate Exhibition Research Competition. She was also selected through a competitive process to present in the I.E. Melhus Graduate Student Symposium titled “What’s in our toolbox to minimize the risk of plant disease?” at the 2013 Annual American Phytopathological Society Meeting in Austin, TX. This is one of the most prestigious awards that graduate students can receive from our national society. We are currently working on publishing these research results several peer-reviewed journals over the upcoming months. How have the results been disseminated to communities of interest? The extension responsibilities of the PIs have facilitated the rapid dissemination of project results to onion producers and interested stakeholders. In Pennsylvania and New York, research results were disseminated at numerous vegetable grower meetings/regional conferences during the course of the project including the Mid-Atlantic Fruit and Vegetable Convention, Empire State Fruit and Vegetable Expo and Lancaster Onion Co-op meeting as well as during the 4th Annual Discovery Day at the Southeast Agricultural Research and Education Center which is geared towards the media and legislators who are interested in learning more about agricultural research that directly impacts the Commonwealth. On a national and international level, results were presented at the 2013 and 2014 American Phytopathological Society meeting in Austin, TX and Minneapolis, MN, respectively, at the 2013 and 2014 W2008 Multi-state regional project meetings in Las Cruces, NM and Denver, CO, the 62nd Annual Muck Crops Research Conference in Bradford, ON in April 2013, University of Wisconsin Extension and WPVGA Grower Conference in February 2013 and Great Lakes Fruit and Vegetable Farm Market EXPO in December 2012. Results were also disseminated throughout the season through one-on-one with the growers collaborating in the intensive field survey project as well as trade journal and newsletter articles. In addition, PIs participated in the Onion ipmPIPE and continued to disseminate the Diagnostic Pocket Series to interested growers and other stakeholders. What do you plan to do during the next reporting period to accomplish the goals? Nothing Reported

Impacts
What was accomplished under these goals? During the past five to ten years, bacterial bulb rots of onion have become the most significant diseases affecting commercial onion production in the Northeast and Mid-Atlantic regions with annual losses ranging from 5 to 40%. Losses are often variable, both between and within fields; in many cases, the full extent of disease loss is not evident until harvest or thereafter. Currently, small-scale diversified fresh markets as well as large-scale onion producers, lack effective tools with which to manage bacterial diseases in onion. The goal of this research was to identify potential sources of the bacterial pathogens as well as environmental and production factors associated with increased bacterial disease losses in order to augment existing disease management recommendations and inform further research into the development of effective management strategies. In PA and NY, a unique on-farm systems approach was used to collect data on forty environmental and management factors from 108 fields over the course of the two-year project. In PA onion transplants, either locally grown or imported from the Southern U.S. and weeds were identified as potential sources of bacterial pathogens in the production system. In addition, factors related to plant nutrition (specifically foliar nitrogen and carbon as well as early season soil nitrate content) and soil temperatures near the physiological onset of onion bulbing were associated with increased bacterial disease incidence at harvest. The data generated from this project has increased our overall knowledge about the bacterial bulb rot - onion pathosystem in the Northeast and Mid-Atlantic regions. Through leveraged funding from the PA Specialty Crop Block Grant Program and state grower associations, plans are underway to conduct replicated research trials to elucidate management practices such as adjusting the timing of nitrogen applications and the use of pre-transplant treatments to improve the management and reduce losses due to bacterial bulb rots of onion. Objective 1. Identify factors associated with bacterial disease incidence in commercial onion fields in order to facilitate the development of an integrated pest management program for onion bacterial diseases in the Northeast region. In PA in 2011 and 2012, replicated on-farm survey plots were established on 28 and 26 farms, respectively to identify potential sources of inoculum as well as production factors related to harvest disease incidence. In NY, replicated plots were established in 22 and 32 fields in 2011 and 2012, respectively. Farms were selected with the assistance of regional extension educators; all PA growers grew ‘Candy’ onions on raised beds with plastic mulch and drip irrigation, fields averaged between 0.5 to 1.0 hectare in size, and were rotated. The majority of PA growers grow transplant onions 15 cm between each plant within the row, four rows across the bed. NY growers grew nine different cultivars (primarily bold cooking onions, with one red cultivar included), which may or may not have been grown on plastic mulch, ranged in size from 2 to 10 hectares, with some fields cropped with onions continuously for over ten years. Forty environmental and production factors were collected at three times during the growing season each year. Bacterial species were detected and identified generally by PCR from sources such as transplants, soil, weeds and harvested bulbs. In PA, pathogenicity tests were conducted with select isolates from each potential inoculum source. Pathogenic isolates of Pectobacterium carotovorum subsp. carotovorum (Pcar), Pantoea agglomerans (Pagg), and Pseudomonas marginalis pv. marginalis (Pmar), were the most common bacterial pathogens in the PA onion cropping system and occurred in soil, transplant and weed tissues, in addition to being present as epiphytes on both onion transplants and common weeds. Pathogenicity tests of Pagg, Pcar, and Pmar isolates from the surfaces and tissue of weeds demonstrated a range in virulence among the weed-derived isolates, ranging from non-pathogenic to highly aggressive. In addition, rep-PCR strain tracking of Pantoea ananatis isolates indicated matching strains from surface-disinfested weed tissue collected at mid-season and a latently infected onion that had been in storage. This suggests that weeds may play a role in onion bacterial diseases by supporting a wide diversity of strains of these bacteria. Pathogenicity testing also suggested that a higher proportion of pathogenic isolates were isolated as epiphytes from the surface of the common weed lambsquarters than from redroot pigweed and purslane. In NY, Burkholderia cepacia was most commonly identified from symptomatic bulbs at harvest with 74% of the finds, followed by Enterobactor cloacea (21%) and Pantoea ananatis (6%). Transplants and weeds were not surveyed for bacteria pathogenic to bacteria in NY. However, B. cepacia was identified in 83% of the soil samples collected in the NY survey. Several lines of evidence support the role of transplants as a source of inoculum. First, a relatively high frequency (22%) of detections of B. gladioli pv. alliicola in symptomatic onions at harvest coincided with a high frequency (64%) of B. gladioli pv. alliicola detected as endophytes from surface-sterilized transplants in 2012. Results from pathogenicity tests on Pcar, Pagg, and Pmar isolates from transplants indicated that over 52% of isolates, regardless of species, isolation location, or pathogenicity test, induced discoloration or maceration on onion. Combined, these results suggest research avenues for more directed disease management strategies for reducing the impact of environmental inoculum sources on bacterial rots of onion. To determine the environmental and management factors associated with high bacterial disease incidence, independent variables were placed in a series of stepwise multiple linear regression models. Foliar nitrogen and foliar carbon were negatively related to total incidence of bacterial rots of onion from the PA datasets, while pre-season levels of soil nitrate were positively related to total incidence of bacterial rots from PA and NY. Foliar nutrient levels implicate early-season fertility in managing bacterial rots of onion, while associations between soil NO3 and rot suggest ammonium or organic N may be more effective N sources in managing bacterial rots. In addition, soil temperatures near the physiological onset of onion bulbing were positively related to total incidence of bacterial rot in PA in 2011 and in the combined NY dataset, which agrees with previously published results. These results suggest greater complexity is necessary for N fertility recommendations: not only should growers be provided with a recommended field rate, but also the timing and type of N applied may play roles in bacterial disease development. In addition, if possible, growers should also take steps to lower soil temperatures, particularly near bulbing. The results of this research have been used to leverage funding to conduct research trials designed to develop more targeted management tools and recommendations related to the source and application timing of nitrogen during the production season, evaluation of cultivar susceptibility and pre-plant treatments to reduce bacterial populations associated with onion transplant. In NY, further research efforts will focus on understanding when onion plants become infected with bacterial pathogens and reducing the inoculum in the soil. The goal of this project is to develop knowledge-based, sustainable and cost-effective management strategies for bacterial diseases of onion in the Northeast and Mid-Atlantic regions. Through funding from the NE-IPM Competitive Grants Program we have been able to greatly advance our understanding of the factors associated with onion bacterial diseases and growers are already augmenting their production practices as a result.

Publications

  • Type: Theses/Dissertations Status: Published Year Published: 2014 Citation: Pfeufer, E.E. 2014. Sources of inoculum, epidemiology, and integrated management of bacterial rots of onion (Allium cepa) with a focus on center rot, caused by Pantoea ananatis and Pantoea aggloerans. Ph.D. Dissertation, The Pennsylvania State University, University Park, PA, August 2014.
  • Type: Journal Articles Status: Published Year Published: 2014 Citation: Bonasera, J.M., J.A. Asselin, and S.V. Beer. 2014. Identification of bacteria pathogenic to or associated with onion (Allium cepacia) based on sequence differences in a portion of the conserved gyrase B gene. Journal of Microbiological Methods 103: 138-143.
  • Type: Conference Papers and Presentations Status: Awaiting Publication Year Published: 2014 Citation: Gugino, B.K., M.A. Mansfield and E.E. Pfeufer. 2014. Bacterial rots of sweet onion in Pennsylvania: tracking sources of infection and targeting critical management points. Phytopathology: S27.
  • Type: Journal Articles Status: Published Year Published: 2013 Citation: Carr, E. A., Zaid, A. M., Bonasera, J. M., Lorbeer, J. W., and Beer, S. V. 2013. Infection of onion leaves by Pantoea ananatis leads to bulb infection. Plant Disease: 97: 1524-1528.


Progress 08/15/12 to 08/14/13

Outputs
Target Audience: All onion growers in the Northeast region stand to benefit from this project. Smaller scale growers sell primarily sweet onions, through local produce auctions and direct markets. These lucrative markets pay $1/lb or more for jumbo and colossal sized bulbs. Reducing losses from bacterial diseases will directly and immediately impact farm profitability. As we succeed in developing an IPM approach to manage bacterial bulb decay that relies heavily on cultural practices, current growers will sustain or increase their acreage and more small-scale diversified vegetable growers will start growing onions, thus building the fresh market onion industry in the Northeast. Reduced incidence of bacterial diseases, especially when it is undetectable in the bulb, will greatly decrease loads being rejected and the dumping of healthy onions along with the rotten ones for large-scale muck onion growers. The results of this research would also be applicable for states such as New Jersey who are looking to build local production to support a processing industry that traditionally ships onions form the Pacific Northwest. The general public will benefit from having affordable locally-grown onions of superior quality available to the year round. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided? Understanding the environmental and on-farm management factors that are contributing to onion yield losses associated with bacterial disease incidence has been the focus of Emily E. Pfeufer’s Ph.D. research in the Department of Plant Pathology and Environmental Microbiology at Penn State. It is anticipated that she will graduate in Spring/Summer of 2014. A research poster presentation given by Emily Pfeufer titled “Common weeds as potential sources of bacterial pathogen inoculum causing onion bulb rots in Pennsylvania” resulting from this research project was awarded 1st place in the Biological Sciences Division at the 2013 Penn State Gamma Sigma Delta Research Competition and 2nd place in the 2013 Penn State Graduate Exhibition Research Competition. She was also selected through a competitive process to present in the I.E. Melhus Graduate Student Symposium titled “What’s in our toolbox to minimize the risk of plant disease?” at the 2013 Annual American Phytopathological Society Meeting in Austin, TX. This is one of the most prestigious awards that graduate students can receive from our national society. How have the results been disseminated to communities of interest? In Pennsylvania and New York, research results were disseminated at several vegetable grower meetings/conferences including the 2013 Mid-Atlantic Fruit and Vegetable Convention and Lancaster Onion Co-op meeting as well as during the 4th Annual Discovery Day at the Southeast Agricultural Research and Education Center which is geared towards the media and legislators who are interested in learning more about agricultural research that directly impacts the Commonwealth. On a national and international level, results were presented at the 2013 American Phytopathological Society meeting in Austin, TX in August 2013, at the W2008 Multi-state regional project meeting in Las Cruces, NM in November 2012, the 62nd Annual Muck Crops Research Conference in Bradford, ON in April 2013, University of Wisconsin Extension and WPVGA Grower Conference in February 2013 and Great Lakes Fruit and Vegetable Farm Market EXPO in December 2012. Results were also disseminated throughout the season through one-on-one with the growers collaborating in the intensive field survey project. In addition, I participated in the Onion ipmPIPE and continued to disseminate the Diagnostic Pocket Series to interested growers and other stakeholders. What do you plan to do during the next reporting period to accomplish the goals? Data analysis from the extensive data set collected in 2011 and 2012 will continue and promises to further elucidate the factors most closely associated with onion bacterial diseases. Identification of these factors will facilitate the development, augmentation and/or implementation of targeted management practices that reduce losses due to bacterial diseases without compromising yield. Based on these results as well as results from trials conducted in previous years, additional field trials will be designed and conducted to better understand the biology and epidemiology of bacterial diseases on onion to further develop integrated disease management strategies that reduce both in-field and post-harvest storage losses.

Impacts
What was accomplished under these goals? In Pennsylvania in 2011 and 2012, replicated on-farm survey plots were established on 28 and 26 farms, respectively to identify potential sources of inoculum as well as production factors related to harvest disease incidence. The extensive dataset generated continues to be a source of new information. A total of 235 bacterial isolates were recovered from 192 samples of the four most common weed species (crabgrass, redroot pigweed, purslane and lambsquarters) collected from commercial onion fields in 2011. Nearly 60% of the culturable bacteria isolated were potential pathogens of onion. Pseudomonas marginalis was commonly cultured from all types of weeds, while Pantoea agglomerans was commonly associated with crabgrass and purslane. Pectobacterium carotovorum was common only to redroot pigweed. Based on pathogenicity tests, all the bacterial isolates from lambsquarters were able to cause onion bulb rots while other weeds were found to have mixed populations of pathogenic and nonpathogenic bacteria on their surfaces. By sampling common weeds are onion fields in 2011, it was shown that weeds are a potential source of bacterial inoculum that causes diseases in onion bulbs. A rep-PCR method was developed to facilitate our ability to track bacterial strains within the same bacterial species. This will enable us to further link bacterial isolates collected from the surface of transplants, weeds, and soil from the on-farm survey plots to those isolated from symptomatic onion bulb tissue at harvest or after storage and further facilitate the development of management strategies to reduce these potential sources of bacterial inoculum. At-planting and at-harvest soil nitrogen, leaf and bulb tissue nitrogen, soil temperature and other factors were analyzed in a multivariate linear regression model. A strong negative relationship between leaf tissue nitrogen at midseason and total harvest losses was suggested, while a positive relationship was also identified between pre-harvest soil temperatures and bacterial disease incidence. These results relate the importance of reducing soil temperatures through use of alternative plastic mulches, ensuring adequate soil fertility early in the season and taking measures to reduce the impact of inoculum sources in the production system. A follow-up replicated field trial was conducted in 2013 to evaluate nitrogen source (calcium nitrate vs. ammonium sulfate) in combination with fertilizer application timing (pre-solstice or full-season). No differences in disease incidence or marketable yield were suggested from plots fertilized with different nitrogen forms however, onions fertilized with ammonium sulfate had significantly higher sulfur content, a key component in onion pungency (P < 0.0001) and not desirable for sweet Spanish-type onions. Collectively, plots inoculated with Pantoea spp. (the causal agents of center rot) had significantly higher disease incidence than uninoculated plots (P = 0.009), and center rot incidence and marketable yield trended based on interactive effects between inoculation status and fertilization timing (P < 0.16). With funding leveraged from the Pennsylvania Vegetable Growers Association, two additional field trials were conducted in 2013 to evaluate the effects of inoculum pressure and onion maturity at harvest on harvest and post-harvest losses due to bacterial diseases caused by several pathogens. The results of this research will provide growers with additional information on the relationship between the timing of harvest and bacterial diseases losses so they can make more informed decisions about when to harvest fields under pressure from bacterial diseases. The data from these two trials is still being analyzed and the first post-harvest storage assessments will begin in October 2013 during the next reporting cycle.

Publications

  • Type: Conference Papers and Presentations Status: Published Year Published: 2012 Citation: C.A. Hoepting. 2012. An IPM approach to managing bacterial diseases of onions. In: Proceedings of the 2012 Great Lakes Fruit, Vegetable and Farm Market EXPO (online): http://www.glexpo.com/summaries/2012 summaries/onion.pdf. Grand Rapids, MI, USA. December 4-6, 2012.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2013 Citation: Pfeufer, E.E., M.A. Mansfield, and B.K. Gugino. 2013. Environmental and management factors associated with bacterial rots of onion in Pennsylvania. Phytopathology 103:S2.173.
  • Type: Other Status: Published Year Published: 2013 Citation: Pfeufer, E.E. and B.K. Gugino. 2013. Environmental factors and production practices associated with bacterial diseases of onion. 2013 Mid-Atlantic Fruit and Vegetable Convention Proceedings, PA Vegetable Growers Association, Richfield, PA. Pp. 171-174.


Progress 08/15/11 to 08/14/12

Outputs
OUTPUTS: Intensive survey plots were established in 28 and 30 onion fields in Pennsylvania and in 22 and 33 onion fields in New York in 2011 and 2012, respectively. In each field, three plots approximately 1 bed (4 to 6 rows/bed) by 30ft long were established. Soil temperature at the 2-in. depth was collected during the growing season in two plots per farm. Bacterial species associated with onion transplants, weeds, and soils were isolated and identified using a combination of culturing and molecular techniques. Mid-season visual bacterial disease and thrips damage assessments were made. Soil inorganic and potentially mineralizable nitrogen levels were assessed in each plot at planting and harvest. At onion bulbing, foliar tissue was harvested for assessment of total nitrogen. At harvest, yield assessments were made on the center 15 ft of bed. Onions were visually assessed for bacterial disease and graded (>4.0 in. colossal, 3.0-4.0 in. jumbo, 2.25-3.0 in. medium, <2.25 in. small). At total of 30 healthy (asymptomatic) onions were dried, placed in storage and reassessed for bacterial disease after four months. Bacterial pathogens were isolated and identified from a sub-set of symptomatic onion bulbs collected at harvest. Twelve seed lots in NY were also sampled for potential bacterial pathogens. In addition in NY, two on-farm small-plot field trials were conducted in 2011 and 2012 in muck onion fields to evaluate the effect of soil nitrogen on bacterial bulb decay. In 2011, 75 lb per acre and 125 lb per acre rates of applied nitrogen were compared and in 2012, 50, 100 and 150 lb per acre of nitrogen were compared. Results of this research thus far have been disseminated in PA and NY via presentations at several vegetable grower meetings/conferences including the Oswego Onion Twilight Meeting, Empire State Fruit and Vegetable Expo, Northeast Vegetable Grower's Meeting and New Holland Vegetable Day attended by over 250 growers and interested stakeholders. In addition, an article was published in the popular trade magazine "Onion World". At the end of the 2011 season, collaborating growers in PA received individual reports sharing their farm specific data and how it ranked compared to other farms participating in this project further increasing grower knowledge and awareness about onion bacterial diseases. PARTICIPANTS: Project directors include: B.K. Gugino, The Pennsylvania State University, C.A. Hoepting, Cornell Cooperative Extension, S.V. Beer, Cornell University. Training and professional development includes: Emily E. Pfeufer, PhD student, Department of Plant Pathology and Environmental Microbiology, The Pennsylvania State University, and Ali M. Zaid, Post-doctoral fellow, Department of Plant Pathology and Plant-Microbe Biology, Cornell University. TARGET AUDIENCES: All onion growers in the Northeast region stand to benefit from this project. Smaller scale growers sell primarily sweet onions, through local produce auctions and direct markets. These lucrative markets pay $1/lb or more for jumbo and colossal sized bulbs. Reducing losses from bacterial diseases will directly and immediately impact farm profitability. As we succeed in developing an IPM approach to manage bacterial bulb decay that relies heavily on cultural practices, current growers will sustain or increase their acreage and more small-scale diversified vegetable growers will start growing onions, thus building the fresh market onion industry in the Northeast. Reduced incidence of bacterial diseases, especially when it is undetectable in the bulb, will greatly decrease loads being rejected and the dumping of healthy onions along with the rotten ones for large-scale muck onion growers. The results of this research would also be applicable for states such as New Jersey who are looking to build local production to support a processing industry that traditionally ships onions form the Pacific Northwest. The general public will benefit from having affordable locally-grown onions of superior quality available to the year round. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.

Impacts
An extensive data set on potential factors associated with onion bacterial diseases has been collected from over 58 and 55 fields in Pennsylvania and New York, respectively during 2011 and 2012. More specifically in NY, 22 and 33 fields were sampled in 2011 and 2012. These represented 7 and 8 growers and 6 and 7 different onion cultivars in 2011 and 2012, all grown on muck soils. In PA, 28 and 30 fields were sampled, one field per grower. All the fields represented onion cv. Candy grown on plastic mulch with drip irrigation on mineral soils. A comprehensive analysis of these data sets promises to elucidate the factors most closely associated with onion bacterial diseases. Identification of these factors will facilitate the development, augmentation and/or implementation of targeted management practices that reduce losses due to bacterial diseases without compromising yield. In PA in 2011, in-field losses from bacterial diseases ranged from 0 to 50.4% with additional storage losses ranging between 2.1 and 41.6%. In NY, losses were considerably less ranging between 0 and 17.3%. Data collection is not complete, but the incidence of bacterial bulb decay at harvest is even lower in 2012. Preliminary analysis of 2011 data in PA correlated warmer mid-season soil temperatures and visual disease ratings to increased in-field losses due to bacterial disease at harvest. More losses also occurred when onions were grown on black as opposed to white plastic; however, this practice is not recommended due to increased pressure from thrips. The bacterial pathogens commonly associated with symptomatic onions at harvest in PA were also associated with onion transplants collected at planting. In New York, preliminary analysis of 2011 data indicated a relationship between soil levels of available nitrogen-nitrogen collected in mid-season (July 7-9 leaf stage) and incidence of bacterial bulb decay at harvest; as soil nitrogen increases bacterial bulb decay increases. More than 78 samples of muck-land soils were collected from fields planted to onions near the time of planting. These samples were analyzed for the presence of bacterial pathogens found earlier to be associated with onions culled by grower-shippers during grading following storage. Samples of seeds and seedling transplants also were analyzed for the presence of bacterial pathogens found earlier to be associated with harvested and stored onions. No bacterial pathogens of consequence were isolated from 12 batches of seed collected from growers. From seedling transplants, many strains of Pantoea agglomerans were isolated. When tested for pathogenicity in the laboratory or greenhouse, all except for two failed to cause symptoms of pathogenicity. Two strains from one batch of transplants caused symptoms of center rot. From the over 78 samples of muck-land soil analyzed, strains of Burkholderia cepacia (causes sour skin) and Enterobacteria cloacae (causes Enterobacter bulb decay) were isolated frequently, while strains of P. ananatis were isolated somewhat less frequently. These survey results suggest that several of the important bulb pathogens of onion overwinter in muck-land soil in New York.

Publications

  • Beer, S. V., J.-A. Asselin, J. M. Bonasera, A. M. Zaid, and C. A. Hoepting. 2012. Research yields greater understanding of bacterial diseases of onion in New York. 2012 Empire State Fruit & Vegetable Expo Proceedings. http://www.hort.cornell.edu/expo/2012proceedings.php.
  • Carr, E. A., A. M. Zaid, J. M. Bonasera, J. W. Lorbeer, and S. V. Beer. 2012. Progression of the center rot pathogen Pantoea ananatis from onion leaves to bulb infection and enhanced pathogenicity assays. Plant Disease (In Review).
  • Hoepting, C. A. 2012. Exploring the relationship between nitrogen and bacterial diseases of onions. In: Proceedings of the 2012 Empire State Fruit and Vegetable Expo, Cornell Cooperative Extension and New York State Vegetable Growers Association. Syracuse, NY, USA. January 24-26, 2012. http://www.hort.cornell.edu/expo/2012proceedings.php.
  • Hoepting, C. A. and S. V. Beer. 2012. Exploring the relationship between nitrogen, plant spacing and bacterial diseases of onion in New York: Reduced nitrogen and closer spacing could result in less rot. Onion World (In Press).
  • Pfeufer, E. E., M. A. Mansfield, J. Stoltzfus, and B. K. Gugino. 2012. Identification of factors associated with bacterial diseases of onion: A case study of two Pennsylvania farms. Phytopathology 102: S1.7.
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