Environmental and management factors associated with bacterial rots of onion in Pennsylvania
E. E. PFEUFER (1), M. A. Mansfield (1), B. K. Gugino (1). (1) Pennsylvania State University, University Park, PA, U.S.A.
Bacterial rots, including center rot (<i>Pantoea ananatis</i> and <i>P. agglomerans</i>), soft rot (<i>Pectobacterium carotovora</i> and <i>Pseudomonas marginalis</i>), and slippery skin (<i>Burkholderia gladioli</i> pv. <i>allicola</i>), are significant diseases of onion in Pennsylvania, and may result in up to 50% yield loss. Growers attempt to manage these diseases using copper fungicides and cultural practices; however, variability in marketable yields still occurs. On-farm trials were conducted in 2011 and 2012 on 28 and 26 farms, respectively, to identify potential sources of inoculum as well as production factors related to harvest disease incidence. At-planting soil, transplant, and midseason weed samples were screened for eight bacterial onion pathogens using a multiplex PCR protocol. At-planting and at-harvest soil N, leaf and bulb tissue N, soil temperature, and other factors were analyzed in a multivariate linear regression model. <i>P. agglomerans</i> and <i>P. marginalis</i> were common on and in over half of onion transplants and were most common on weed surfaces. A strong negative relationship between leaf tissue N at midseason and total harvest losses was suggested in a multivariate linear regression model, while a positive relationship was suggested between preharvest soil temperatures and disease. These results relate the importance of reducing soil temperatures, ensuring adequate soil fertility early in the season, and taking measures to reduce the impact of inoculum sources in the production system.
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