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Disease Note

Occurrence of Bacterial Stem Rot Caused by Pseudomonas cichorii in Greenhouse-grown Lettuce in Ontario. B. N. Dhanvantari, Research Station, Agriculture Canada, Harrow, Ontario, N0R 1G0. . Plant Dis. 74:394. Accepted for publication 16 January 1990. . DOI: 10.1094/PD-74-0394A.

A firm dark-brown stem rot and necrotic streaking on petioles of inner leaves were observed on lettuce (Lactuca sativa L. 'Butterhead') grown with the nutrient film technique in a Norfolk County greenhouse. These symptoms were observed when the plants were near maturity and after the heads were cut open. About 10% of the plants in a 0.4-ha area were affected. Isolations from infected tissue consistently yielded motile, gram-negative bacteria identified as Pseudomonas cichorii (Swingle) Stapp according to the results of LOPAT and other key tests in Bergey's Manual of Systematic Bacteriology (1984). The isolated bacteria were pathogenic to celery, chrysanthemum, lettuce, and tomato upon wound inoculation of young potted plants with toothpicks dipped in 2- to 3-day-old colonies on King's medium B. Lesions were produced in tissue adjacent to and distal from the point of inoculation in 10 days (celery, chrysanthemum, and lettuce) to 14 days (tomato) after moist-chamber incubation for the first 2 days. This is the first report for Ontario of the disease, which appears to be similar to varnish spot of California field-grown lettuce (1).

Reference: (1) R. G. Grogan et al. Phytopathology 67:957, 1977.