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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). |