Responding to growers' needs: Evaluation of management strategies for onion center rot, caused by Pantoea ananatis and Pantoea agglomerans

Open Access
Mazzone, Jennie Diehl
Graduate Program:
Plant Pathology
Master of Science
Document Type:
Master Thesis
Date of Defense:
November 29, 2016
Committee Members:
  • Dr. Beth K. Gugino, Thesis Advisor/Co-Advisor
  • Dr. María del Mar Jiménez Gasco, Committee Member
  • Dr. Kari A. Peter, Committee Member
  • Dr. William Lamont, Jr., Committee Member
  • onion
  • Pantoea ananatis
  • Pantoea agglomerans
  • center rot
  • cultivar
  • nitrogen
  • transplant
  • bactericide
  • management
  • integrated pest management
  • Allium cepa
  • bacteria
  • disease
  • Honduras
  • horticultural production guide
  • Rhizoctonia solani
  • tomato
  • tomato foliar blight
  • Pennsylvania
Onion growers in Pennsylvania are continually challenged by in-field and post-harvest yield losses due to bacterial pathogens. In 2013, losses due to bacterial disease reduced the number of marketable onion boxes over 40%, resulting in a total loss of $488,000. The primary bacterial pathogens in Pennsylvania include the onion center rot pathogens Pantoea ananatis and Pantoea agglomerans and are the focus of this research. Although, there are a number of cultural and in-season management practices currently used by growers to reduce the risk of center rot, unacceptable losses still frequently occur and there is a need to develop more targeted strategies that can be incorporated into an integrated pest management program. The three management strategies evaluated in this research were cultivar selection, augmented nitrogen fertigation programs and pre-plant onion transplant treatments. Currently, there are no known onion breeding programs targeting center rot, nor have there been many trials to evaluate the susceptibility of commercially available cultivars. To address this knowledge gap, thirteen onion cultivars were evaluated between 2015 and 2016 for center rot susceptibility, marketability and select horticultural characteristics. The only cultivar to have lower disease incidence and severity and comparable yields to grower standard cv. Candy was cv. Spanish Medallion. Preliminary data suggested that applying total crop nitrogen prior to onion bulbing increased total yield and reduced bacterial disease incidence. Also, it was observed that low lying areas in heavily manured fields used for onion production have had up to 83% bacterial bulb decay incidence at harvest. Based on this knowledge, we evaluated whether the timing and rate of nitrogen application could reduce center rot losses at harvest. A positive, quadratic relationship was found between foliar nitrogen levels at bulbing and center rot incidence at harvest. An interaction existed between rate and time but trends in this relationship were variable based on field trial location. Eliminating P. ananatis and P. agglomerans prior to planting through use of a transplant bactericide could reduce a potential source of inoculum and provide growers with another management tool. Hydrogen dioxide, hydrogen peroxide with mono- and di-potassium salts of phosphorus acid, copper sulfate pentahydrate and streptomycin sulfate were all effective at reducing P. ananatis and P. agglomerans as epiphytes on onion transplants and in-vitro. The results of this research would also be widely applicable to other onion production systems and has been influential in the development of a horticultural production guide to aid professionals and growers in low-input horticulture and disease management decisions in Honduras. The results of this research have increased the collective knowledge on the potential use of cultivar selection, nitrogen application rate and timing and bactericide sensitivity to manage onion center rot and will be used to provide growers higher precision disease management options.