Ken Pernezny, Lawrence Datnoff, and Richard Lentini2 1. This document is PP126, one of a series of the Plant Pathology Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Original publication date March 1994. Reviewed May 2009. Visit the EDIS Web site at http://edis.ifas.ufl.edu. 2. Ken Pernezny, Professor, Plant Pathology; Lawrence Datnoff, Former Associate Professor, Plant Pathology; Richard Lentini, Sr. Biological Scientist; Everglades Research and Education Center, IFAS, University of Florida, Belle Glade, FL 33430. The term "plates," where used in this document, refers to color photographs that can be displayed on screen from CD-ROM. These photographs are not included in the printed document. Sporadic outbreaks of a petiole necrosis of celery (Apium graveolens var. dulce), known locally as "brown stem", have been observed in Florida for over 40 years. In the 1992-93 winter vegetable season, a particularly severe outbreak of brown stem occurred in celery production fields throughout the Everglades Agricultural Area (EAA). One hundred percent of all fields surveyed had some brown stem, with average incidence about 5%. Losses to the industry were estimated at $5 million. At that time, no specific cause for brown stem had been established. The prevailing opinion was the disease was an environmental or physiological problem. The severe outbreak prompted a more thorough investigation into its cause. The research uncovered a common bacterial pathogen as the origin of the disease. Brown stem symptoms consist of a firm, brown discoloration throughout the petiole. Damage is especially evident in the heart region at the base of the stalk, but brown streaks may be seen along most of the length of the petiole (Plate 1 and Plate 2). Browning is confined to the ground parenchyma; vascular bundles appear as islands of healthy green among diseased cortical and pith tissues (Plate 3). The symptoms become more pronounced as celery approaches harvest maturity.
Brown Stem in Florida Celery 2 The isolation and identification of the causal agent of brown stem was recently made and the report has been submitted to the journal, Plant Disease. It was demonstrated that brown stem disease of celery is caused by the bacterium Pseudomonas cichorii. This is the same pathogen that causes bacterial blight of celery. Indeed, tests confirmed that bacterial strains recovered from brown stem lesions are indistinguishable from those causing typical bacterial blight lesions on celery leaf blades. Reports of brown stem are made only about every five or six years, whereas leaf spot symptoms caused by Pseudomonas cichorii are a yearly occurrence. The reasons for the sporadic nature of brown stem outbreaks are unknown. The weather in the winter of 1992-93 was unusual, with frequent rainfall and strong winds. These conditions, along with high humidity, might be essential for brown stem expression. Documented reports of weather conditions linked to brown stem incidence are lacking. Identification of environmental conditions important to brown stem development is the subject of current research. Do not apply foliar nitrogen during seasons favorable for bacterial blight and avoid over-fertilization with soil applied nitrogen. To help prevent the spread of the bacterium keep workers and farm equipment from brushing against wet plants. In the future, it may be possible to use varieties of celery with limited resistance to brown stem.