Development of Enterobacter cloacae on onion plants, and effect of post-harvest curing temperature on development of Enterobacter bulb decay

• Published in: Phytopathology 2008-06, Vol.98 (6), p.S142-S142
• Main Authors: Schroeder, B K, Thyren, E, Sires, J L, du Toit, LJ
• Format: Article
• Language: English
• Subjects: Allium cepa; Enterobacter; Enterobacter cloacae
• ISSN: 0031-949X

Enterobacter cloacae was associated with an outbreak of Enterobaeter bulb decay of onion bulbs that caused economic losses during the 2004-05 storage season in Washington State. Trials were initiated to assess: 1) survival of E. cloacae on onion foliage, and 2) the effect of post-harvest curing temperature on development of Enterobaeter bulb decay in storage. A rifampicin-resistant strain of E. cloacae was mist-inoculated (10 super(3) and 10 super(5) cfu/ml) onto foliage of 5 to 8 week-old plants of the cultivar 'Vaquero' maintained in a humidity chamber. Bacteria were isolated from 5 replicate plants at inoculation, and weekly thereafter to quantify the population of E. cloacae. In addition, onion bulbs of 'Redwing' and 'Vaquero' were injected with 5 x 10 super(7) cfu E. cloacae/bulb, and then heat-cured at 25, 30, 35, or 40C for 2 or 14 days. Storage temperature was then decreased to 4C at a rate of 2.5C/day. Four replicates of 5 bulbs/curing temperature/curing duration were evaluated for symptoms after 1, 2, and 3 months of storage at 4C. E. cloacae populations on inoculated onion leaves remained >10 super(3) cfu/ml. In the storage trial, severity of Enterobaeter bulb decay increased with increasing curing temperature for both durations of curing. The research will clarify the ability of E. cloacae to maintain populations on onion foliage, the relationship of this to bulb infection, and the impact of post-harvest curing temperature on development of Enterobaeter bulb decay in storage.