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Project Leader: Helene R. Dillard, Cornell University, NYSAES,
Department of Plant Pathology, Geneva, NY 14456
Cooperators: Carol MacNeil, Extension Vegetable Area Specialist; Abby
Seaman, Extension IPM Area Specialist; John Gibbons, CCE; Meg McGrath, Long
Island Horticultural Research Lab
Abstract (nontechnical):
The objective of this study was to identify sources of on-farm inoculum of
Clavibacter michiganensis subsp. michiganensis (CMM), the causal
agent of bacterial canker of tomatoes. Two hundred ninety seven samples from
inanimate (swabbing from walls, floor, wood, hoses, etc.) and animate sources
(weeds, other plants, tomatoes) from 3 commercial greenhouses were tested to see
if they carried the CMM pathogen. A wide variety of methods were utilized in
attempts to conclusively identify the bacteria, including an agglutination kit
and a commercial diagnostic testing service that used a quick ELISA test. Any
bacteria isolated that were likely to be the pathogen were further tested to see
if they could cause disease on tomatoes. The various isolation procedures were
cumbersome, slow, expensive, and difficult to interpret since none were
diagnostic alone. The disease organism is difficult to isolate, identify
conclusively, and even more difficult to prove to cause disease.
The tomato transplants from one of the commercial grower’s greenhouses were
subsequently planted in 2 locations. In the commercial field where bacterial
canker occurred 3 years previously, moderate disease developed on the leaves and
fruit starting at fruit load. Disease also occurred in transplants planted on
"new" ground, as well as on tomato volunteers from an area with canker in 1999.
The transplants appeared to be harboring the disease in the planted fields, but
contaminated seed or overwintering debris or weeds or other crops seemed to be
the source of inoculum for the volunteers. Weather is obviously a driving factor
in disease development, since the disease has varied from severe, moderate, to
low over three consecutive years at one location. Bacterial canker did not
develop in a sample of the same transplants that were grown in a field in Geneva
that did not have a history of bacterial canker. Transplants from the other 2
growers did not develop bacterial canker in the greenhouses or in the fields.
There are no highly effective chemical control measures for bacterial canker.
Disease control starts with clean seed and continues with good sanitation
practices in the greenhouse. This includes disinfecting surfaces in the seedling
greenhouse and sanitizing any reused equipment or supplies. Bacteria may survive
as an epiphyte on other plants present in a greenhouse. Epiphytes do not cause
disease on plants, but will grow and multiply on non-host plants, which become
an inoculation source for susceptible plants such as tomatoes. The best practice
is to dedicate a greenhouse to tomato production and avoid co-mingling tomato
transplants with transplants of ornamentals or other crops. Avoid damage to the
tomato plants since damage from storms, wind, blowing soil, mechanical damage,
handling, etc. followed by water may increase a population above threshold level
and cause or promote disease. Careful management practices are key to mitigate
the impact of this disease. |
