Celery (Apium graveolens) is grown extensively in the coastal counties (Ventura, Santa Barbara, San Luis Obispo, Monterey, and Santa Cruz) of California. In 2004 and 2005, field plantings of celery in Ventura and Monterey counties showed symptoms of a petiole and crown rot. Initial symptoms consisted of a light tan discoloration at the crowns and on outer petioles that were in contact with soil. These discolored areas developed a soft, brown, watery rot. Affected petioles wilted and later collapsed. White mycelium and small (0.5 to 3.0 mm in diameter), irregularly shaped, black sclerotia formed on diseased tissues. Isolations from symptomatic petioles, crowns, mycelium, and sclerotia produced colonies of Sclerotinia minor. Eight-week-old celery transplants (cv. Conquistador) grown in a peat-moss based rooting medium in 10-cm2 pots were used to test pathogenicity. Colonized agar plugs (one plug per plant) from eight celery isolates were inserted into slots made in the potting mix adjacent to the crowns and lower petioles of the transplants. Noncolonized plugs were placed in slots for control celery plants. Twenty plants were used for each isolate and control, and all test plants were incubated in a greenhouse at 21 to 23°C. Disease development was rapid, and after 4 days, inoculated celery plants exhibited brown necrosis at inoculation points. After 9 days, celery crowns were decayed and petioles collapsed. S. minor was reisolated from necrotic crown and petiole tissues. Noninoculated plants were asymptomatic. The experiment was repeated and results were similar. To our knowledge, this is the first report of celery as a host of S. minor in California (2). In the United States, S. minor has been reported on celery in Florida (1). Celery in California is only occasionally infected by S. minor and is more often infected by S. sclerotiorum.
Reference: (1) D. F. Farr et al. Fungi on Plants and Plant Products in the United States. The American Phytopathological Society. St. Paul, MN, 1989. (2) M. S. Melzer et al. Can. J. Plant Pathol. 19:272, 1997.
