PURDUE UNIVERSITY
BP-8-17 January 1974

BACTERIAL CANKER OF TOMATO W. R. Stevenson, D. H. Scott, P. C. Pecknold Extension Plant Pathologists

Bacterial canker is potentially one of the most destructive diseases of tomato.
Caused by the bacterium Corynebacterium michiganense (Smith) Jensen, canker is distributed throughout the world in every major tomato-growing region. Only sound management practices based upon correct diagnosis and application of control measures will reduce the prevalence of this disease.

Symptoms of Bacterial Canker

Plants may be infected at any stage of growth. Seedlings that may be infected at planting time usually cannot be distinguished from healthy seedlings until several days after transplanting in the greenhouse or field. Wilting of infected plants is generally the first noticeable symptom. Initially, lower leaves wilt and curl upwards with recovery during nighttime periods. Leaflets on one side of the petiole wilt at first with the entire leaf wilting eventually.
Wilting proceeds slowly upwards to uppermost leaves, which eventually die from the margins inward. The petiole, however, characteristically remains green and firm-ly attached to the main plant stem. Yellow to dark brown streaking on the surface of stems and petioles may accompany wilting. Streaks may break open in late stages of development to form cankers. As the disease progresses, pith tissue becomes yellow to brown in color with soft cavities at variable intervals. When a stem from an infected plant is cut lengthwise, a light
yellow to tan-colored streak may be observed just beyond the vascular tissue.
These streaks appear similar to streaks associated with infection by Fusarium and Verticillium. Thus, diagnosis on the basis of streaking alone is not a reliable diagnostic symptom. Such streaking does not occur in the roots of plants infected with canker.

Fruit symptoms include a birds-eye spotting of fruits. Margins of spots are white and flat while centers are tan colored, small, and raised. Fruits from infected plants are often stunted in size, show a mottling of the surface and a ribbed appearance, and may fall prematurely from infected plants.

Control

Once introduced to field or greenhouse tomato plantings, the bacterial canker pathogen is extremely difficult to control. Fungicides commonly used for disease control in tomato production have little or no effect on the canker bacterium. Fixed copper sprays may help to reduce secondary spread, but do not prevent spread completely. The use of air blast sprayers in canker infected fields may, in fact, aid in field movement of bacteria by blowing bacteria from infected to healthy plants. Superficial wounds created by blowing water droplets and small particles of soil allow easy entrance of bacteria into the plant.

Control can be achieved by careful

COOPERATIVE EXTENSION SERVICE, PURDUE UNIVERSITY, WEST LAFAYETTE, INDIANA
Department of Botany and Plant Pathology, Life Science Building